Transcript Intro Bio Chapter 8-9-10 Fall 2012

Chapter 8
Cellular Reproduction: Cells from Cells
PowerPoint® Lectures for
Campbell Essential Biology, Fifth Edition, and
Campbell Essential Biology with Physiology,
Fourth Edition
– Eric J. Simon, Jean L. Dickey, and Jane B. Reece
Lectures by Edward J. Zalisko
© 2013 Pearson Education, Inc.
Biology and Society:
Virgin Birth of a Dragon
• In 2002, zookeepers at the Chester Zoo were
surprised to discover that their Komodo Dragon
laid eggs.
– The female dragon had not been in the company of
a male.
– The eggs developed without fertilization, in a
process called parthenogenesis.
– DNA analysis confirmed that her offspring had
genes only from her.
© 2013 Pearson Education, Inc.
Biology and Society:
Virgin Birth of a Dragon
• A second European Komodo dragon is now known
to have reproduced
– asexually, via parthenogenesis, and
– sexually.
© 2013 Pearson Education, Inc.
Figure 8.0
WHAT CELL REPRODUCTION
ACCOMPLISHES
• Reproduction
– may result in the birth of new organisms but
– more commonly involves the production of new
cells.
• When a cell undergoes reproduction, or cell
division, two “daughter” cells are produced that
are genetically identical
– to each other and
– to the “parent” cell.
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WHAT CELL REPRODUCTION
ACCOMPLISHES
• Before a parent cell splits into two, it duplicates its
chromosomes, the structures that contain most
of the cell’s DNA.
• During cell division, each daughter cell receives
one identical set of chromosomes from the lone,
original parent cell.
© 2013 Pearson Education, Inc.
WHAT CELL REPRODUCTION
ACCOMPLISHES
• Cell division plays important roles in the lives of
organisms.
• Cell division
– replaces damaged or lost cells,
– permits growth, and
– allows for reproduction.
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Figure 8.1a
FUNCTIONS OF CELL DIVISION
Colorized SEM
Growth via Cell Division
LM
Cell Replacement
Human kidney cell
Early human embryo
WHAT CELL REPRODUCTION
ACCOMPLISHES
• In asexual reproduction,
– single-celled organisms reproduce by simple cell
division and
– there is no fertilization of an egg by a sperm.
• Some multicellular organisms, such as sea stars,
can grow new individuals from fragmented pieces.
• Growing a new plant from a clipping is another
example of asexual reproduction.
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Figure 8.1b
FUNCTIONS OF CELL DIVISION
LM
Asexual Reproduction
Division of an amoeba
Regeneration of a sea star
Growth of a clipping
WHAT CELL REPRODUCTION
ACCOMPLISHES
• In asexual reproduction, the lone parent and its
offspring have identical genes.
• Mitosis is the type of cell division responsible for
– asexual reproduction and
– growth and maintenance of multicellular
organisms.
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WHAT CELL REPRODUCTION
ACCOMPLISHES
• Sexual reproduction requires fertilization of an
egg by a sperm using a special type of cell division
called meiosis.
• Thus, sexually reproducing organisms use
– meiosis for reproduction and
– mitosis for growth and maintenance.
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THE CELL CYCLE AND MITOSIS
• In a eukaryotic cell,
– most genes are located on chromosomes in the
cell nucleus and
– a few genes are found in DNA in mitochondria and
chloroplasts.
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Eukaryotic Chromosomes
• Each eukaryotic chromosome contains one very
long DNA molecule, typically bearing thousands of
genes.
• The number of chromosomes in a eukaryotic cell
depends on the species.
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Figure 8.2
Species
Indian muntjac deer
Koala
Opossum
Giraffe
Mouse
Human
Duck-billed platypus
Buffalo
Dog
Red viscacha
rat
Number of chromosomes in body cells
6
16
22
30
40
46
54
60
78
102
Eukaryotic Chromosomes
• Chromosomes are
– made of chromatin, fibers composed of roughly
equal amounts of DNA and protein molecules and
– not visible in a cell until cell division occurs.
© 2013 Pearson Education, Inc.
LM
Figure 8.3
Chromosomes
Figure 8.4
DNA double helix
Histones
TEM
“Beads
on a
string”
Nucleosome
Tight helical fiber
Duplicated
chromosomes
(sister
chromatids)
TEM
Thick supercoil
Centromere
Eukaryotic Chromosomes
• Before a cell divides, it duplicates all of its
chromosomes, resulting in two copies called sister
chromatids containing identical genes.
• Two sister chromatids are joined together tightly at
a narrow “waist” called the centromere.
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Eukaryotic Chromosomes
• When the cell divides, the sister chromatids of a
duplicated chromosome separate from each other.
• Once separated, each chromatid is
– considered a full-fledged chromosome and
– identical to the original chromosome.
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Figure 8.5
Chromosome
duplication
Sister
chromatids
Chromosome
distribution to
daughter cells
The Cell Cycle
• A cell cycle is the ordered sequence of events that
extend
– from the time a cell is first formed from a dividing
parent cell
– to its own division into two cells.
• The cell cycle consists of two distinct phases:
1. interphase and
2. the mitotic phase.
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Figure 8.6
S phase
(DNA synthesis; chromosome duplication)
Interphase: metabolism and
growth (90% of time)
G1
G2
Mitotic
(M) phase:
cell division
(10% of time)
Cytokinesis
(division of
cytoplasm)
Mitosis
(division
of nucleus)
The Cell Cycle
• Most of a cell cycle is spent in interphase.
• During interphase, a cell
– performs its normal functions,
– doubles everything in its cytoplasm, and
– grows in size.
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The Cell Cycle
• The mitotic (M) phase includes two overlapping
processes:
1. mitosis, in which the nucleus and its contents
divide evenly into two daughter nuclei and
2. cytokinesis, in which the cytoplasm is divided in
two.
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Mitosis and Cytokinesis
• Mitosis consists of four distinct phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
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Figure 8.7a
INTERPHASE
Centrosomes
(with centriole
pairs)
Chromatin
PROPHASE
Early mitotic
spindle
Centrosome
Fragments of
nuclear envelope
Centromere
Nuclear
envelope
Plasma
membrane
Chromosome
(two sister chromatids)
Spindle microtubules
Figure 8.7b
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Nuclear
envelope
forming
Spindle
Daughter
chromosomes
Cleavage
furrow
Mitosis and Cytokinesis
• Cytokinesis usually
– begins during telophase,
– divides the cytoplasm, and
– is different in plant and animal cells.
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Mitosis and Cytokinesis
• In animal cells, cytokinesis
– is known as cleavage and
– begins with the appearance of a cleavage furrow,
an indentation at the equator of the cell.
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SEM
Figure 8.8a
Cleavage
furrow
Cleavage furrow
Contracting ring of
microfilaments
Daughter cells
Mitosis and Cytokinesis
• In plant cells, cytokinesis begins when vesicles
containing cell wall material collect at the middle of
the cell and then fuse, forming a membranous disk
called the cell plate.
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Figure 8.8b
Daughter nucleus
LM
Wall of parent cell
Cell plate
forming
Cell wall
Vesicles containing
cell wall material
Cell plate
New cell wall
Daughter cells
Cancer Cells: Growing Out of Control
• Normal plant and animal cells have a cell cycle
control system that consists of specialized
proteins, which send “stop” and “go-ahead” signals
at certain key points during the cell cycle.
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What Is Cancer?
• Cancer is a disease of the cell cycle.
• Cancer cells do not respond normally to the cell
cycle control system.
• Cancer cells can form tumors, abnormally growing
masses of body cells.
• If the abnormal cells remain at the original site, the
lump is called a benign tumor.
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What Is Cancer?
• The spread of cancer cells beyond their original
site of origin is metastasis.
• Malignant tumors can
– spread to other parts of the body and
– interrupt normal body functions.
• A person with a malignant tumor is said to have
cancer.
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Figure 8.9
Lymph
vessels
Tumor
Blood
vessel
Glandular
tissue
A tumor grows
from a single
cancer cell.
Cancer cells invade
neighboring tissue.
Metastasis: Cancer
cells spread through
lymph and blood
vessels to other parts
of the body.
MEIOSIS, THE BASIS OF SEXUAL
REPRODUCTION
• Sexual reproduction
– depends on meiosis and fertilization and
– produces offspring that contain a unique
combination of genes from the parents.
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Figure 8.10
Homologous Chromosomes
• Different individuals of a single species have the
same
– number and
– types of chromosomes.
• A human somatic cell
– is a typical body cell and
– has 46 chromosomes.
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Homologous Chromosomes
• A karyotype is an image that reveals an orderly
arrangement of chromosomes.
• Homologous chromosomes
– are matching pairs of chromosomes that
– can possess different versions of the same genes.
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Pair of homologous
chromosomes
Centromere
One
duplicated
chromosome
Sister
chromatids
LM
Figure 8.11
Homologous Chromosomes
• Humans have
– two different sex chromosomes, X and Y, and
– 22 pairs of matching chromosomes, called
autosomes.
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Gametes and the Life Cycle of a Sexual Organism
• The life cycle of a multicellular organism is the
sequence of stages leading from the adults of one
generation to the adults of the next.
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Figure 8.12
Haploid gametes (n  23)
n
Egg cell
n
Sperm cell
MEIOSIS
FERTILIZATION
Multicellular
diploid adults
(2n  46)
2n
Diploid
zygote
(2n  46)
MITOSIS
and development
Key
Haploid (n)
Diploid (2n)
Gametes and the Life Cycle of a Sexual Organism
• Humans are diploid organisms with
– body cells containing two sets of chromosomes
and
– haploid gametes that have only one member of
each homologous pair of chromosomes.
• In humans, a haploid sperm fuses with a haploid
egg during fertilization to form a diploid zygote.
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Gametes and the Life Cycle of a Sexual Organism
• Sexual life cycles involve an alternation of diploid
and haploid stages.
• Meiosis produces haploid gametes, which keeps
the chromosome number from doubling every
generation.
© 2013 Pearson Education, Inc.
Figure 8.13-3
1
Chromosomes
duplicate.
Pair of
homologous
chromosomes
in diploid
parent cell
2
Duplicated pair
of homologous
chromosomes
INTERPHASE BEFORE MEIOSIS
Homologous
chromosomes
separate.
3
Sister chromatids
separate.
Sister
chromatids
MEIOSIS I
MEIOSIS II
The Process of Meiosis
• In meiosis,
– haploid daughter cells are produced in diploid
organisms,
– interphase is followed by two consecutive
divisions, meiosis I and meiosis II, and
– crossing over occurs.
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Figure 8.14a
MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE
INTERPHASE
Centrosomes
(with centriole pairs)
PROPHASE I
Sites of
crossing over
Spindle
Nuclear Chromatin
envelope
Chromosomes
duplicate.
Sister
chromatids
Pair of
homologous
chromosomes
Homologous
chromosomes
pair up and
exchange
segments.
METAPHASE I
Microtubules
attached to
chromosome
ANAPHASE I
Sister chromatids
remain attached
Centromere
Pairs of
homologous
chromosomes
line up.
Pairs of
homologous
chromosomes
split up.
Figure 8.14b
MEIOSIS II: SISTER CHROMATIDS SEPARATE
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND
CYTOKINESIS
Sister
chromatids
separate
Haploid
daughter
cells forming
Cleavage
furrow
Two haploid
cells form;
chromosomes
are still doubled.
During another round of cell division, the sister
chromatids finally separate; four haploid
daughter cells result, containing single
chromosomes.
Review: Comparing Mitosis and Meiosis
• In mitosis and meiosis, the chromosomes duplicate
only once, during the preceding interphase.
• The number of cell divisions varies:
– Mitosis uses one division and produces two
diploid cells.
– Meiosis uses two divisions and produces four
haploid cells.
• All the events unique to meiosis occur during
meiosis I.
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Figure 8.15
MITOSIS
MEIOSIS
Prophase I
Prophase
Duplicated
chromosome
MEIOSIS I
Parent cell
Metaphase I
Metaphase
Chromosomes
align.
Sister
chromatids
separate.
Homologous
pairs align.
Anaphase I
Telophase I
Anaphase
Telophase
2n
Site of
crossing
over
2n
MEIOSIS I
Homologous
chromosomes
separate.
Haploid
n2
MEIOSIS II
Sister
chromatids
separate.
n
n
n
n
The Origins of Genetic Variation
• Offspring of sexual reproduction are genetically
different from their parents and one another.
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Independent Assortment of Chromosomes
• When aligned during metaphase I of meiosis, the
side-by-side orientation of each homologous pair
of chromosomes is a matter of chance.
• Every chromosome pair orients independently of
all of the others at metaphase I.
• For any species, the total number of chromosome
combinations that can appear in the gametes due
to independent assortment is
– 2n, where n is the haploid number.
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Independent Assortment of Chromosomes
• For a human,
– n = 23.
– With n = 23, there are 8,388,608 different
chromosome combinations possible in a gamete.
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Random Fertilization
• A human egg cell is fertilized randomly by one
sperm, leading to genetic variety in the zygote.
• If each gamete represents one of 8,388,608
different chromosome combinations, at fertilization,
humans would have 8,388,608 × 8,388,608, or
more than 70 trillion different possible chromosome
combinations.
• So we see that the random nature of fertilization
adds a huge amount of potential variability to the
offspring of sexual reproduction.
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Colorized LM
Figure 8.17
When Meiosis Goes Awry
• What happens when errors occur in meiosis?
• Such mistakes can result in genetic abnormalities
that range from mild to fatal.
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How Accidents during Meiosis Can Alter Chromosome
Number
• In nondisjunction,
– the members of a chromosome pair fail to separate
at anaphase,
– producing gametes with an incorrect number of
chromosomes.
• Nondisjunction can occur during meiosis I or II.
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Figure 8.20-3
NONDISJUNCTION IN MEIOSIS I
NONDISJUNCTION IN MEIOSIS II
Meiosis I
Homologous
chromosomes fail
to separate.
Meiosis II
Sister
chromatids
fail to
separate.
Gametes
n1
n1
n–1
Abnormal
n–1
n1
n–1
Abnormal
n
n
Normal
How Accidents during Meiosis Can Alter Chromosome
Number
• If nondisjunction occurs, and a normal sperm
fertilizes an egg with an extra chromosome, the
result is a zygote with a total of 2n + 1
chromosomes.
• If the organism survives, it will have
– an abnormal karyotype and
– probably a syndrome of disorders caused by the
abnormal number of genes.
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Figure 8.21
Abnormal egg
cell with extra
chromosome
n1
Normal
sperm cell
n (normal)
Abnormal zygote with
extra chromosome
2n  1
Down Syndrome: An Extra Chromosome 21
• Down syndrome
– is also called trisomy 21,
– is a condition in which an individual has an extra
chromosome 21, and
– affects about one out of every 700 children.
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LM
Figure 8.22
Trisomy 21
Down Syndrome: An Extra Chromosome 21
• The incidence of Down syndrome in the offspring
of normal parents increases markedly with the age
of the mother.
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Figure 8.23
Infants with Down syndrome
(per 1,000 births)
90
80
70
60
50
40
30
20
10
0
20
25
30
35
40
Age of mother
45
50
Figure 8.UN02
Chromosome (one
long piece of DNA)
Centromere
Sister
chromatids
Duplicated chromosome
Figure 8.UN03
S phase
DNA synthesis; chromosome duplication
Interphase
Cell growth and
chromosome duplication
G2
G1
Mitotic
(M) phase
Genetically
identical
“daughter”
cells
Cytokinesis
(division of
cytoplasm)
Mitosis
(division of
nucleus)
Figure 8.UN04
Human Life Cycle
Haploid gametes (n  23)
Key
Haploid (n)
n
Diploid (2n)
Egg cell
n
Sperm cell
FERTILIZATION
MEIOSIS
Male and female
diploid adults
(2n  46)
MITOSIS
and development
2n
Diploid
zygote
(2n  46)
Figure 8.UN05
MITOSIS
MEIOSIS
Parent
cell (2n)
MEIOSIS I
Parent
cell (2n)
Chromosome Chromosome
duplication
duplication
Pairing of
homologous
chromosome
Crossing
over
Daughter
cells
2n
2n
MEIOSIS II
n
n
n
Daughter cells
n
LM
Figure 8.UN06
(a)
(b)
(c)
(d)
Chapter 9
Patterns of Inheritance
Biology and Society:
Our Longest-Running Genetic Experiment:
Dogs
• People have selected and mated dogs with
preferred traits for more than 15,000 years.
• Over thousands of years, such genetic tinkering
has led to the incredible variety of body types
and behaviors in dogs today.
• The biological principles underlying genetics
have only recently been understood.
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Figure 9.0
HERITABLE VARIATION AND
PATTERNS OF INHERITANCE
• Heredity is the transmission of traits from one
generation to the next.
• Genetics is the scientific study of heredity.
• Gregor Mendel
– worked in the 1860s,
– was the first person to analyze patterns of
inheritance, and
– deduced the fundamental principles of genetics.
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Figure 9.1
In an Abbey Garden
• Mendel studied garden peas because they
– were easy to grow,
– came in many readily distinguishable varieties,
– are easily manipulated, and
– can self-fertilize.
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In an Abbey Garden
• A character is a heritable feature that varies
among individuals.
• A trait is a variant of a character.
• Each of the characters Mendel studied occurred in
two distinct traits.
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In an Abbey Garden
• Mendel
– created purebred varieties of plants and
– crossed two different purebred varieties.
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In an Abbey Garden
• Hybrids are the offspring of two different
purebred varieties.
– The parental plants are the P generation.
– Their hybrid offspring are the F1 generation.
– A cross of the F1 plants forms the F2 generation.
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Mendel’s Law of Segregation
• Mendel performed many experiments.
• He tracked the inheritance of characters that occur
as two alternative traits.
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Figure 9.4
Dominant
Dominant
Recessive
Pod
shape
Flower
color
Inflated
Purple
White
Flower
position
Seed
color
Seed
shape
Recessive
Axial
Terminal
Yellow
Green
Round
Wrinkled
Constricted
Pod
color
Green
Yellow
Tall
Dwarf
Stem
length
Figure 9.4a
Monohybrid Crosses
• A monohybrid cross is a cross between purebred
parent plants that differ in only one character.
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Figure 9.5-3
P Generation
(purebred
parents)
Purple
flowers
White
flowers
F1 Generation
All plants have
purple flowers
Fertilization
among F1 plants
(F1  F1)
F2 Generation
3
4 of plants
have purple flowers
1
4 of plants
have white flowers
Figure 9.5a
Monohybrid Crosses
• Mendel developed four hypotheses from the
monohybrid cross, listed here using modern
terminology (including “gene” instead of “heritable
factor”).
1. The alternative versions of genes are called
alleles.
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Monohybrid Crosses
2. For each inherited character, an organism inherits
two alleles, one from each parent.
– An organism is homozygous for that gene if both
alleles are identical.
– An organism is heterozygous for that gene if the
alleles are different.
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Monohybrid Crosses
3. If two alleles of an inherited pair differ,
– then one determines the organism’s appearance
and is called the dominant allele and
– the other has no noticeable effect on the organism’s
appearance and is called the recessive allele.
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Monohybrid Crosses
4. Gametes carry only one allele for each inherited
character.
– The two alleles for a character segregate (separate)
from each other during the production of gametes.
– This statement is called the law of segregation.
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Monohybrid Crosses
• Do Mendel’s hypotheses account for the 3:1 ratio
he observed in the F2 generation?
• A Punnett square highlights
– the four possible combinations of gametes and
– the four possible offspring in the F2 generation.
© 2013 Pearson Education, Inc.
Figure 9.6
P Generation
Genetic makeup (alleles)
Purple flowers
Alleles carried
PP
by parents
Gametes
White flowers
pp
All p
All P
F1 Generation
(hybrids)
Purple flowers
All Pp
Alleles
segregate
Gametes
1
P
2
F2 Generation
(hybrids)
1 p
2
Sperm from
F1 plant
P
p
PP
Pp
Pp
pp
P
Eggs from
F1 plant
p
Phenotypic ratio Genotypic ratio
3 purple : 1 white 1 PP : 2 Pp : 1 pp
Monohybrid Crosses
• Geneticists distinguish between an organism’s
physical appearance and its genetic makeup.
– An organism’s physical appearance is its
phenotype.
– An organism’s genetic makeup is its genotype.
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Genetic Alleles and Homologous Chromosomes
• A gene locus is a specific location of a gene along
a chromosome.
• Homologous chromosomes have alleles (alternate
versions) of a gene at the same locus.
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Figure 9.7
Homologous
chromosomes
Gene loci
Genotype:
Dominant
allele
P
a
B
P
a
b
PP
Homozygous
for the
dominant allele
aa
Homozygous
for the
recessive allele
Recessive
allele
Bb
Heterozygous
with one dominant
and one recessive
allele
Mendel’s Law of Independent Assortment
• A dihybrid cross is the mating of parental
varieties differing in two characters.
• What would result from a dihybrid cross? Two
hypotheses are possible:
1. dependent assortment or
2. independent assortment.
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Figure 9.8
(a) Hypothesis:
Dependent assortment
(b) Hypothesis:
Independent assortment
P Generation
RRYY
rryy
RRYY
Gametes RY
Gametes RY
ry
F1 Generation
rryy
ry
RrYy
RrYy
Sperm
F2 Generation
1
4
RY
1
4
rY
1
4
Ry
1
4
ry
Sperm
1
2
RY
1
2
ry
1
2
RY
Eggs
1
2
ry
Predicted results
(not actually seen)
1
4 RY
1
4
RRYY RrYY RRYy RrYy
rY
RrYY rrYY RrYy rrYy
Eggs
1
4
Ry
1
4
ry
RRYy RrYy RRyy Rryy
RrYy rrYy Rryy rryy
Actual results
(support hypothesis)
9
16
Yellow
round
3
16
Green
round
3
16
Yellow
wrinkled
1
16
Green
wrinkled
DOMINANT TRAITS
Figure 9.12
Widow’s peak
Free earlobe
No freckles
Straight hairline
Attached earlobe
RECESSIVE TRAITS
Freckles
Family Pedigrees
• A family pedigree
– shows the history of a trait in a family and
– allows geneticists to analyze human traits.
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Figure 9.13
First generation
(grandparents)
Second generation
(parents, aunts, and
uncles)
Third generation
(brother and
sister)
Aaron
Ff
Betty
Ff
Evelyn Fred Gabe Hal
FF
ff
ff
Ff
or
Ff
Kevin
ff
Female Male
Attached
Female Male
Free
Cletus
ff
Ina
Ff
Lisa
FF
or
Ff
Debra
Ff
Jill
ff
Human Disorders Controlled by a Single Gene
• Many human traits
– show simple inheritance patterns and
– are controlled by single genes on autosomes.
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Table 9.1
Recessive Disorders
• Most human genetic disorders are recessive.
• Individuals who have the recessive allele but
appear normal are carriers of the disorder.
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Figure 9.16
Parents
Normal
(no achondroplasia)
dd
Dwarf
(achondroplasia)
Dd
d Sperm
D
d
Dd
Dwarf
Dd
Dwarf
dd
Normal
dd
Normal
Eggs
d
Jeremy
Molly Jo
Jacob
Zachary
Matt
Amy
Genetic Testing
• Today many tests can detect the presence of
disease-causing alleles.
• Most genetic tests are performed during
pregnancy.
– Amniocentesis collects cells from amniotic fluid.
– Chorionic villus sampling removes cells from
placental tissue.
• Genetic counseling helps patients understand the
results and implications of genetic testing.
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The Role of Environment
• Many human characters result from a combination
of
– heredity and
– environment.
• Only genetic influences are inherited.
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Figure 9.29b
X
Colorized SEM
Y
Sex Determination in Humans
• Nearly all mammals have a pair of sex
chromosomes designated X and Y.
– Males have an X and Y.
– Females have XX.
© 2013 Pearson Education, Inc.
Sex-Linked Genes
• Any gene located on a sex chromosome is called a
sex-linked gene.
– Most sex-linked genes are found on the X
chromosome.
– Red-green colorblindness is
– a common human sex-linked disorder and
– caused by a malfunction of light-sensitive cells in
the eyes.
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Sex-Linked Genes
• Hemophilia
– is a sex-linked recessive blood-clotting trait that
may result in excessive bleeding and death after
relatively minor cuts and bruises and
– has plagued the royal families of Europe.
© 2013 Pearson Education, Inc.
Figure 9.UN08
Chapter 10
The Structure and Function of DNA
DNA: STRUCTURE AND REPLICATION
• DNA
– was known to be a chemical in cells by the end of
the nineteenth century,
– has the capacity to store genetic information, and
– can be copied and passed from generation to
generation.
• The discovery of DNA as the hereditary material
ushered in the new field of molecular biology, the
study of heredity at the molecular level.
© 2013 Pearson Education, Inc.
DNA and RNA Structure
• DNA and RNA are nucleic acids.
– They consist of chemical units called nucleotides.
– A nucleotide polymer is a polynucleotide.
– Nucleotides are joined by covalent bonds between
the sugar of one nucleotide and the phosphate of
the next, forming a sugar-phosphate backbone.
© 2013 Pearson Education, Inc.
Figure 10.1
Phosphate
group
Nitrogenous base
Sugar
DNA
nucleotide
DNA
double
helix
Nitrogenous base
(can be A, G, C, or T)
Thymine (T)
Phosphate
group
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate
backbone
DNA and RNA Structure
• The sugar in DNA is deoxyribose. Thus, the full
name for DNA is deoxyribonucleic acid.
© 2013 Pearson Education, Inc.
DNA and RNA Structure
• The four nucleotides found in DNA differ in their
nitrogenous bases. These bases are
– thymine (T),
– cytosine (C),
– adenine (A), and
– guanine (G).
• RNA has uracil (U) in place of thymine.
© 2013 Pearson Education, Inc.
Watson and Crick’s Discovery of the Double
Helix
• James Watson and Francis Crick determined that
DNA is a double helix.
• Watson and Crick used X-ray crystallography data
to reveal the basic shape of DNA.
• Rosalind Franklin produced the X-ray image of
DNA.
© 2013 Pearson Education, Inc.
Figure 10.3a
James Watson (left) and Francis Crick
Watson and Crick’s Discovery of the Double Helix
• The model of DNA is like a rope ladder twisted into
a spiral.
– The ropes at the sides represent the sugarphosphate backbones.
– Each wooden rung represents a pair of bases
connected by hydrogen bonds.
© 2013 Pearson Education, Inc.
Figure 10.4
Twist
Watson and Crick’s Discovery of the Double Helix
• DNA bases pair in a complementary fashion:
– adenine (A) pairs with thymine (T) and
– cytosine (C) pairs with guanine (G).
© 2013 Pearson Education, Inc.
Figure 10.5
Hydrogen bond
(a) Ribbon model
(b) Atomic model
(c) Computer model
DNA Replication
• When a cell reproduces, a complete copy of the
DNA must pass from one generation to the next.
• Watson and Crick’s model for DNA suggested that
DNA replicates by a template mechanism.
© 2013 Pearson Education, Inc.
Figure 10.6
Parental (old)
DNA molecule
Daughter
(new) strand
Parental
(old) strand
Daughter DNA
molecules
(double helices)
DNA Replication
• DNA can be damaged by X-rays and ultraviolet
light.
• DNA polymerases
– are enzymes,
– make the covalent bonds between the nucleotides
of a new DNA strand, and
– are involved in repairing damaged DNA.
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DNA Replication
• DNA replication ensures that all the body cells in
multicellular organisms carry the same genetic
information.
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DNA Replication
• DNA replication in eukaryotes
– begins at specific sites on a double helix (called
origins of replication) and
– proceeds in both directions.
© 2013 Pearson Education, Inc.
Figure 10.7
Origin of
replication
Origin of
replication
Parental strands
Origin of
replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
THE FLOW OF GENETIC
INFORMATION FROM DNA TO RNA TO
PROTEIN
• DNA provides instructions to
– a cell and
– an organism as a whole.
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How an Organism’s Genotype Determines Its
Phenotype
• An organism’s genotype is its genetic makeup, the
sequence of nucleotide bases in DNA.
• The phenotype is the organism’s physical traits,
which arise from the actions of a wide variety of
proteins.
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How an Organism’s Genotype Determines Its
Phenotype
• DNA specifies the synthesis of proteins in two
stages:
1. transcription, the transfer of genetic information
from DNA into an RNA molecule and
2. translation, the transfer of information from RNA
into a protein.
© 2013 Pearson Education, Inc.
Figure 10.8-3
DNA
TRANSCRIPTION
Nucleus
RNA
Cytoplasm
TRANSLATION
Protein
From Nucleotides to Amino Acids: An Overview
• Genetic information in DNA is
– transcribed into RNA, then
– translated into polypeptides,
– which then fold into proteins.
© 2013 Pearson Education, Inc.
From Nucleotides to Amino Acids: An Overview
• What is the language of nucleic acids?
– In DNA, it is the linear sequence of nucleotide
bases.
– A typical gene consists of thousands of nucleotides
in a specific sequence.
• When a segment of DNA is transcribed, the result
is an RNA molecule.
• RNA is then translated into a sequence of amino
acids in a polypeptide.
© 2013 Pearson Education, Inc.
Figure 10.10
Gene 1
Gene 2
DNA molecule
Gene 3
DNA strand
TRANSCRIPTION
RNA
TRANSLATION
Codon
Polypeptide
Amino acid
From Nucleotides to Amino Acids: An Overview
• Experiments have verified that the flow of
information from gene to protein is based on a
triplet code.
• A codon is a triplet of bases, which codes for one
amino acid.
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The Genetic Code
• The genetic code is the set of rules that convert a
nucleotide sequence in RNA to an amino acid
sequence.
• Of the 64 triplets,
– 61 code for amino acids and
– 3 are stop codons, instructing the ribosomes to end
the polypeptide.
© 2013 Pearson Education, Inc.
Figure 10.11
Second base of RNA codon
UUU
U
UUC
UUA
UUG
UCU
Phenylalanine
UCC
(Phe)
Leucine
(Leu)
First base of RNA codon
CUU
C
CUC
CUA
A
Leucine
(Leu)
A
UAU
UGA Stop
UCG
UAG
Stop
UGG Tryptophan (Trp) G
CCU
CAU
CCC
CCA
Proline
(Pro)
CAC
CAA
ACU
AAU
ACC
ACA
AAC
Threonine
(Thr)
AAA
ACG
AAG
GCU
GAU
Met or start
GUU
GUC
GUA
GUG
Valine
(Val)
U
Stop
AUU
AUG
Cysteine
(Cys)
UAA
UCA
CAG
Isoleucine
(Ile)
UGU
UAC
Serine
(Ser)
CCG
AUC
G
Tyrosine
(Tyr)
CUG
AUA
G
C
GCC
GCA
GCG
Alanine
(Ala)
GAC
GAA
GAG
Histidine
(His)
Glutamine
(Gln)
UGC
CGU
CGC
CGA
Lysine
(Lys)
Aspartic
acid (Asp)
Glutamic
acid (Glu)
AGA
AGG
Arginine
(Arg)
GGA
GGG
C
A
G
Serine
(Ser)
Arginine
(Arg)
GGU
GGC
A
U
CGG
AGU
Asparagine
AGC
(Asn)
C
U
C
A
G
U
Glycine
(Gly)
C
A
G
Third base of RNA codon
U
The Genetic Code
• Because diverse organisms share a common
genetic code, it is possible to program one species
to produce a protein from another species by
transplanting DNA.
© 2013 Pearson Education, Inc.
Figure 10.12
Transcription: From DNA to RNA
• Transcription
– makes RNA from a DNA template,
– uses a process that resembles the synthesis of a
DNA strand during DNA replication, and
– substitutes uracil (U) for thymine (T).
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Transcription: From DNA to RNA
• RNA nucleotides are linked by the transcription
enzyme RNA polymerase.
© 2013 Pearson Education, Inc.
Figure 10.13
RNA polymerase
DNA of gene
Promoter
DNA
1 Initiation
RNA
Terminator
DNA
2 Elongation
RNA nucleotides
RNA polymerase
3 Termination
Growing RNA
Newly
made
RNA
Direction of
transcription
Completed RNA
Template
strand of DNA
(a) A close-up view of transcription
RNA
polymerase
(b) Transcription of a gene
Initiation of Transcription
• The “start transcribing” signal is a nucleotide
sequence called a promoter, which is
– located in the DNA at the beginning of the gene
and
– a specific place where RNA polymerase attaches.
• The first phase of transcription is initiation, in which
– RNA polymerase attaches to the promoter and
– RNA synthesis begins.
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RNA Elongation
• During the second phase of transcription, called
elongation,
– the RNA grows longer and
– the RNA strand peels away from its DNA template.
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Termination of Transcription
• During the third phase of transcription, called
termination,
– RNA polymerase reaches a special sequence of
bases in the DNA template called a terminator,
signaling the end of the gene,
– polymerase detaches from the RNA and the gene,
and
– the DNA strands rejoin.
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The Processing of Eukaryotic RNA
• In the cells of prokaryotes, RNA transcribed from a
gene immediately functions as messenger RNA
(mRNA), the molecule that is translated into
protein.
• The eukaryotic cell
– localizes transcription in the nucleus and
– modifies, or processes, the RNA transcripts in the
nucleus before they move to the cytoplasm for
translation by ribosomes.
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Translation: The Players
• Translation is the conversion from the nucleic acid
language to the protein language.
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Messenger RNA (mRNA)
• Translation requires
– mRNA,
– ATP,
– enzymes,
– ribosomes, and
– transfer RNA (tRNA).
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Transfer RNA (tRNA)
• Transfer RNA (tRNA)
– acts as a molecular interpreter,
– carries amino acids, and
– matches amino acids with codons in mRNA using
anticodons, a special triplet of bases that is
complementary to a codon triplet on mRNA.
© 2013 Pearson Education, Inc.
Figure 10.15
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
tRNA polynucleotide
(ribbon model)
tRNA
(simplified
representation)
Ribosomes
• Ribosomes are organelles that
– coordinate the functions of mRNA and tRNA and
– are made of two subunits.
• Each subunit is made up of
– proteins and
– a considerable amount of another kind of RNA,
ribosomal RNA (rRNA).
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Ribosomes
• A fully assembled ribosome holds tRNA and
mRNA for use in translation.
© 2013 Pearson Education, Inc.
Figure 10.16
Next amino acid
to be added to
polypeptide
tRNA
binding sites
P site
Growing
polypeptide
A site
mRNA
binding
site
(a) A simplified diagram
of a ribosome
tRNA
Large
Ribosome
subunit
mRNA
Small
subunit
Codons
(b) The “players” of translation
Review: DNA RNA Protein
• In a cell, genetic information flows from
– DNA to RNA in the nucleus and
– RNA to protein in the cytoplasm.
© 2013 Pearson Education, Inc.
Figure 10.20-6
RNA polymerase
1 Transcription
Nucleus
DNA
mRNA
Intron
Anticodon
2 RNA processing
Codon
Cap
Tail
Intron
mRNA
5 Elongation
Polypeptide
Amino acid
tRNA
A
Ribosomal
subunits
Stop
codon
Anticodon
ATP
Enzyme
3 Amino acid attachment
4 Initiation of
translation
6 Termination
Review: DNA RNA Protein
• As it is made, a polypeptide
– coils and folds and
– assumes a three-dimensional shape, its tertiary
structure.
• Transcription and translation are how genes
control the structures and activities of cells.
© 2013 Pearson Education, Inc.
Mutations
• A mutation is any change in the nucleotide
sequence of DNA.
• Mutations can change the amino acids in a protein.
• Mutations can involve
– large regions of a chromosome or
– just a single nucleotide pair, as occurs in sickle-cell
disease.
© 2013 Pearson Education, Inc.
Figure 10.21
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
Types of Mutations
• Mutations within a gene can be divided into two
general categories:
1. nucleotide substitutions (the replacement of one
base by another) and
2. nucleotide deletions or insertions (the loss or
addition of a nucleotide).
• Insertions and deletions can
– change the reading frame of the genetic message
and
– lead to disastrous effects.
© 2013 Pearson Education, Inc.
Figure 10.22
Met
Lys
Phe
Gly
mRNA and protein from a normal gene
Met
Lys
Phe
Ser
Ala
Ala
(a) Base substitution
Deleted
Met
Lys
Leu
Ala
(b) Nucleotide deletion
Inserted
Met
Lys
Leu
(c) Nucleotide insertion
Trp
Arg
Figure 10.22a
Met
Lys
Phe
Ala
Gly
mRNA and protein from a normal gene
Met
Lys
Phe
(a) Base substitution
Ser
Ala
Figure 10.22b
Met
Lys
Phe
Ala
Gly
mRNA and protein from a normal gene
Deleted
Met
Lys
Leu
(b) Nucleotide deletion
Ala
Figure 10.22c
Met
Lys
Phe
Ala
Gly
mRNA and protein from a normal gene
Inserted
Met
Lys
Leu
(c) Nucleotide insertion
Trp
Arg
Mutagens
• Mutations may result from
– errors in DNA replication or recombination or
– physical or chemical agents called mutagens.
• Mutations
– are often harmful but
– are useful in nature and the laboratory as a source
of genetic diversity, which makes evolution by
natural selection possible.
© 2013 Pearson Education, Inc.
Figure 10.23
Figure 10.UN03a
Nitrogenous
base
Phosphate
group
DNA
Sugar
Polynucleotide
Nucleotide
Figure 10.UN03b
Nitrogenous
base
Sugar
Number of
strands
DNA
RNA
C
G
A
T
C
G
A
U
DeoxyRibose
ribose
2
1
Figure 10.UN04
Parental
DNA
molecule
New
daughter
strand
Identical
daughter
DNA molecules
Figure 10.UN05
TRANSCRIPTION
TRANSLATION
Gene
mRNA
DNA
Polypeptide
Figure 10.UN06
Growing
polypeptide
Amino acid
Large ribosomal
subunit
tRNA
mRNA
Anticodon
Codons
Small ribosomal
subunit
Figure 10.UN07