Transcript AP Biology Chapter 6

AP Biology
Chapter 6
Dr. Laurie Solis
Eukaryotic Cells
• A Eukaryotic cell is a three-dimensional
structure composed of carbohydrates, lipids
(fats), nucleic acids, and proteins.
It all starts with a cell…
Cells are the basic unit of life in all
living organisms
Life on earth…
• Life on earth can be
traced back 3.7 billion
years beginning in the
form of a single celled
organism
• Cells of all living
organisms share
similarities as part of our
common evolutionary
past.
– Our focus is on eukaryotic
cells because they are
found in multi-cellular
organisms.
Eukaryotic Cells
• A Eukaryotic cell is a three-dimensional
structure composed of carbohydrates, lipids
(fats), nucleic acids, and proteins.
Eukaryotic Cells, contd.
DNA and RNA – genetic info that
controls the cells functions
(deoxyribonucleic acid) and
(ribonucleic acid)
Mitochondriaresponsible for
producing energy;
contain their own
distinct DNA –
mitochondrial DNA;
inherited only from the
mother
Ribosomes –
essential to
protein synthesis
Cytoplasm – gel like structure
that protects the nucleus
DNA
•
DNA is the very basis
of life!
– Watson and Crick
discover DNA in
1953. (Cambridge
University)
– Revolutionized
biology, medicine
and the
understanding of
evolutionary
processes.
James Watson (left) and Francis Crick in 1953
DNA: We share 50% of our DNA
with bananas…
• The genetic code is universal
• DNA is the genetic material in all
forms of life
• The DNA of all organisms is
composed of the same molecules
– For example, the same code CGA
specifies amino acid alanine –
regardless of the species.
• DNA is like a universal language.
• DNA shows us the connectivity
between all living things -- the
biological relationship between all
living things.
• What makes species unique is not
differences in DNA material, but
differences in how the DNA material
Other DNA facts you don't need to know:
- A parent and child share 99.5% of the
same DNA.
- We share 40-50% of our DNA with
cabbages.
- Humans share 98% of their DNA with
chimpanzees.
- Every human on earth shares 99% of their
DNA with every other human.
- Identical twins share the exact same DNA
- meaning their DNA is 100% identical.
- We share 60% of our DNA with a fruit fly.
- Researchers at Cambridge University are
convinced that the mud worms not only
share DNA with humans but that they are
also our closest invertabrae relatives.
DNA contd.
•
The DNA molecule is made of
up two chains of smaller
molecules called nucleotides.
– Forms a double helix shape
– Nucleotides are composed
of sugar, phosphate, and
one of four DNA bases.
Bases and bonds
• Bases are: adenine (A),
guanine (G), thymine
(T), and cytosine (C)
• One type of base can
only bond with another
type (i.e. A to T and G
to C)
•
This is essential to DNA’s
ability to replicate itself.
Sugars and phosphates
DNA bases
• The four bases of DNA
–
–
–
–
A = Adenine
G = Guanine
T = Thymine
C = Cytosine
A
T
C
G
T
A
G
C
– http://nobelprize.org/educational_games/m
edicine/dna_double_helix/
DNA Replication
• Cells have to multiply
• Cell multiplication is made
possible by cell division
• Cells multiply in a way that
each new cell receives a
full set of genetic material
– This is important because
a cell can’t function
properly without the right
amount of DNA
– For this to happen, DNA
must first replicate
DNA Replication
• Before a cell divides, enzymes,
break the bonds between bases of
the DNA molecules
• The exposed bases attract
unattached DNA nucleotides,
present in the cell nucleus
• Since each base can only pair with
only one another, the attraction
between bases occurs in a
complementary way.
– That means the previously
joined parental nucleotide
chains serve as models or
templates for forming the new
strands of nucleotides.
Characteristics of DNA
1. The DNA Code is universal – same basic messages
apply to all life forms on the planet from bacteria to
mammals
2. The DNA Code is triplet – each amino acid is specified
by a sequence of three bases in the mRNA, which in
turn is coded for by three bases in the DNA
3. The DNA Code is continuous – without pauses.
4. The DNA Code is redundant – it replicates itself
Protein Synthesis
• One of the most important
activities of DNA is to direct the
manufacture of proteins.
– Collagen: structural
component of tissue (skin)
– Hemogloben: carries oxygen
throughout the body
– Enzymes: lactase, breaks
down lactose.
– Hormones
• Insulin: allows the liver
and muscle tissue to
absorb glucose
Amino Acids
•
•
•
•
•
Proteins are made up of chains of
smaller molecules called amino
acids.
What makes proteins different from one
another is the number and sequence of
their amino acids.
There are 20 amino acids, combined
in different amounts and sequences to
produce at least 90,000 different
proteins.
For a protein to function properly –
amino acids must be arranged in their
proper sequence
Amino acids – small molecules that are
the components of proteins
Protein Synthesis contd.
• Regulatory Proteins – enter a cells
nucleus and attach directly to the DNA
– Regulate DNA activity
• Protein Synthesis has to occur
accurately - if it doesn’t, psychological
and cellular activities can be disrupted
or even prevented.
• Ribonucleic acid (RNA) – a single
stranded molecule, similar in structure
to DNA. Three forms of RNA are
The term synthesis (from the ancient
Greek σύνθεσις σύν "with" and θέσις
essential to protein synthesis. These
"placing") is used in many fields, usually to
are messenger RNA, transfer RNA,
mean a process which combines together
two or more pre-existing elements resulting
and ribosomal RNA.
in the formation of something new. The
verb would be to synthesize meaning to
make or form a synthesis. Synthesis may
refer to:
messenger RNA
The first step in protein synthesis is to copy the DNA message into
a form of ribonucleic acid called mRNA.
 messenger RNA - a form of RNA that is assembled on a sequence
of DNA bases. This carries the DNA to the ribosomes during protein
synthesis.
 This is the first step in protein synthesis is to copy the DNA
message into a form of ribonucleic acid called mRNA.
 This takes place outside the cell nucleus in the cytoplasm

RNA differs from DNA in these ways:
 It’s single stranded
 It contains a different type of sugar
 It contains the base uracil as a substitute for the DNA base thymine.
transfer RNA
– transfer RNA (tRNA) – the type of RNA that
binds to specific amino acids and transports
them to the ribosome during protein synthesis.
Ribosomal DNA
• Ribosomes are composed of a form of RNA and
protein. Essential to the manufacture of proteins.
Protein Synthesis contd
• Exons
– Segments of genes
involved in protein
synthesis
• Ex means they are
expressed
• Introns
– Segments of genes
initially transcribed and
then deleted; therefore
they are not expressed –
therefore are not involved
in protein synthesis
•
Exons and introns refer to
specific nucleotide base
sequences in the genetic code
that are involved in producing
proteins. Exons are the DNA
bases that are transcribed into
mRNA and eventually code for
amino acids in the proteins.
Introns are DNA bases, which
are found between exons, but
are not expressed. Genes which
contain introns are known as
interrupted genes.
What is a Gene?
•
•
•
gene – a sequence of DNA bases that
specifies the order (or sequence) of amino
acids in an entire protein, a portion of a protein,
or any functional product.
– A gene may be made up of hundreds or
thousands of DNA bases organized into
coding and non-coding segments.
The gene codes for production of a
polypeptide chain.
– Polypeptide chain – A sequence of amino
acids that may act alone or in combination
with others as a functional protein.
A gene may be composed of only a few
hundred bases, or thousands.
Regulatory Genes
• Some genes act solely to control the expression of
other genes
– These genes can switch other genes “on” or “off”.
Regulatory Genes
• An example of regulatory
genes concerns DNA
deactivation during
embryonic development
– While all somatic cells contain
the same information, only
some of the cells will actually
manifest
• For example, both the cells
of the stomach lining and
the cells in bones have
DNA that codes for the
production of digestive
enzymes. Regulatory
enzymes ensure that only
the stomach lining will
produce the digestive
enzymes – i.e. to ensure
each part of the body
produces and functions
properly
Regulatory Genes contd.
• Types of Regulatory Genes
– Homeobox (Hox) genes: Extremely important gene. An
evolutionary ancient family of regulatory genes that
directs the development of the overall body plan and the
segmentation of body tissue.
• It interacts with other genes to determine the identity and
characteristics of body segments and structures, but not
their actual development.
– Determines where limbs occur
– Establishes the pattern and number of vertebrae
– Hox genes are present in all insects and vertebrates and
don’t vary greatly from species to species.
Hox genes contd.
• Hox genes are important
because they are conserved
– meaning they don’t really
change from species to
species – they are the pretty
much the same.
– Hox genes evolved from genes
present in the earliest forms of life.
– Hox genes are responsible for various
physical differences between closely
related species, like humans and
chimps.
Mutation
• If the sequence of bases is altered by a mutation –
then the manufacture of proteins can’t happen, and
the cell may not function properly or not at all.
– Mutation – A change in DNA . Mutation refers to
changes in DNA bases (specifically called point
mutations) as well as to changes chromosome number
and/or structure.
Harmless changes like flower color….
Mutation contd.
• One example of a mutation is ‘sickle cell anemia’.
– Sickle cell anemia: A severe inherited hemoglobin disorder in
which red blood cells collapse when deprived of oxygen. It
results from inheriting two copies (from both parents) of the
mutant allele. This allele is caused by a single base
substitution in the DNA.
• People become anemic through loss of oxygen and get
sick (impaired circulation from blocked capillaries,
destruction of red blood cells, oxygen deprivation to the
vital organs, can lead to death).
• However, people who only inherit the gene from one
parent don’t get sickle cell anemia.
Sickle Cell Anemia• In fact, people with sickle cell
have an immunity to malaria.
• Sickle cell anemia is an example
of a point mutation; a chemical
change in a single base of a
DNA sequence.
Sickle Cell Anemia-• According to the National Heart, Lung, and Blood
Institute of the NIH, about 72,000 Americans are
affected by sickle cell anemia (NHLBI 2003). In addition,
about two million Americans are estimated to have
sickle cell trait (they are carriers of the sickle cell allele)
(NHLBI 2003). The sickle cell allele is much more
common to certain ethnic groups; the allele is most
frequent in people with Central or South American,
Cuban, Indian, Saudi Arabian, Mediterranean, or African
ancestries (NHLBI 2003). One in 600 African-Americans
and one in 1000-1400 Hispanic Americans are born with
sickle cell anemia (NHLBI 2003).
Chromosomes
• When cells divide to produce new
cells, chromatin (which is loose
diffused DNA – granular
substance) becomes tightly coiled
into chromosomes.
• Chromosomes: discrete
structures composed of DNA and
protein found only in the nuclei of
cells. Chromosomes are visible
under magnification only during
certain phases of cell division.
Chromosomes
• Chromosomes are composed of DNA and proteins.
• The two strands you see are a result of the DNA
replicating itself. One strand of the chromosome is an
exact copy of another.
Chromosomes
• Humans have 46 chromosomes
– Chimpanzees and Gorillas have 48
– Humans don’t have less DNA – ours is just packaged differently.
• There are two types of chromosomes
– Autosomes – carry genetic information that govern all physical
characteristics except sex determination
– Sex chromosomes –
• X and Y
• Y – in mammals the Y determines maleness
• X – is more like an autosome, because it is the “default”
setting.
• Offspring inherit one member of each chromosomal pair
from their father and mother.
• These chromosomal pairs govern the same traits
Chromosomes
• Chromosomes contain almost
all of the genetic information
that determines inheritance.
• Different plant and animal
species have different shapes
and numbers of
chromosomes.
• Having more chromosomes
does not necessarily mean
that an organism is
structurally more complex.
• Having the same number of
chromosomes does not mean
that two animals are the
same species.
Species
# of
Chromosomes
Cat
38
Pig
38
Cow
60
Goat
60
Dog
78
Chicken
78
Oxytricha (single
celled organism)
46 million!
Cell Division
• Cell division is called mitosis
– Simple cell division – the way cells reproduce. This
is what all cells do.
• Meiosis – may lead to the development of new
individuals since it produced reproductive cells, or
gametes. “Cell division in specialized cells in
female ovaries and male testes. Meiosis involves
two divisions and results in four daughter cells,
each containing only half the original number of
chromosomes.” If it weren’t cut in half, then it
wouldn’t be possible to maintain the same number
of chromosomes from one generation to the next.
Meiosis
• Meiosis is evolutionarily significant because
– Increases genetic variation in populations
– Ensures we are not ‘clones’
– Each individual represents a unique combination of genes
due to the random assortment of chromosomes.
Meiosis
• If problems occur during meiosis and
chromosomes don’t separate properly,
the result will be 45 or 47 chromosomes.
• Most of the time this is lethal- except in
one case.
• Down syndrome or Trisomy 21, is when
there are 3 copies of chromosome 21.
– Health affects: susceptibility to leukemia,
congenital heart defects, and mental impairment.
– Most affected infants are born to women 35 and
older.
New Frontiers
• Advancements in the last two decades
– Recombinant DNA technology
• Inject human genes that produce proteins in bacteria in
order to produce insulin
• Human Genome Project: entire genetic makeup of an individual or
species
– Began in 1990 and completed in 2003.
– International effort aimed at sequencing and mapping the
entire human genome.
– Human genome is comprised of 3 billion bases and
30,000 genes.
• Important in biomedical research
• How different genes function