Transcript Biology Mid-term Notes

5.1 The Cell Cycle
KEY CONCEPT
Cells have distinct phases of growth, reproduction,
and normal functions.
5.1 The Cell Cycle
• The cell cycle is a regular pattern of growth, DNA
replication, and cell division.
5.1 The Cell Cycle
• The main stages of the cell cycle are gap 1, synthesis, gap
2, and mitosis.
– Gap 1 (G1): cell growth and
normal functions
– DNA synthesis (S): copies
DNA
– Gap 2 (G2): additional
growth
– Mitosis (M): includes
division of the cell nucleus
(mitosis) and division of the
cell cytoplasm (cytokinesis)
• Mitosis occurs only if the cell is large enough and the DNA
undamaged.
5.1 The Cell Cycle
Cells divide at different rates.
• The rate of cell division varies with the need for those
types of cells.
• Some cells are unlikely to divide (G0).
5.2 Mitosis and Cytokinesis
KEY CONCEPT
Cells divide during mitosis and cytokinesis.
5.2 Mitosis and Cytokinesis
Chromosomes condense at the start of mitosis.
• DNA wraps around proteins (histones) that condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
5.2 Mitosis and Cytokinesis
• DNA plus proteins is called chromatin.
chromatid
• One half of a duplicated
chromosome is a chromatid.
• Sister chromatids are held
together at the centromere.
• Telomeres protect DNA and do
not include genes.
telomere
centromere
telomere
Condensed, duplicated chromosome
5.2 Mitosis and Cytokinesis
Mitosis and cytokinesis produce two genetically identical
daughter cells.
Parent cell
• Interphase prepares
the cell to divide.
• During interphase,
the DNA is
duplicated.
centrioles
spindle fibers
centrosome
nucleus with
DNA
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During prophase, chromosomes condense and
spindle fibers form.
5.2 Mitosis and Cytokinesis
– During metaphase, chromosomes line up in the
middle of the cell.
5.2 Mitosis and Cytokinesis
– During anaphase, sister chromatids separate to
opposite sides of the cell.
5.2 Mitosis and Cytokinesis
– During telophase, the new nuclei form and
chromosomes begin to uncoil.
5.2 Mitosis and Cytokinesis
• Cytokinesis differs in animal and plant cells.
– In animal cells, the
membrane pinches
closed.
– In plant cells, a cell
plate forms.
5.3 Regulation of the Cell Cycle
KEY CONCEPT
Cell cycle regulation is necessary for healthy
growth.
5.3 Regulation of the Cell Cycle
Factors inside & outside cell can regulate cell division.
• Death of nearby cells can speed up cell division.
• Proteins & hormones can both activate and/or prevent
cell division.
• Over crowding can slow cell division.
5.3 Regulation of the Cell Cycle
• Apoptosis is programmed cell death.
– a normal feature of healthy organisms
– caused by a cell’s production of self-destructive
enzymes
– Human embryos have webbing between their fingers
and toes. Before the baby is born the cells undergo
apoptosis and they are born with unwebbed fingers
and toes.
webbed fingers
5.3 Regulation of the Cell Cycle
Cell division is uncontrolled in cancer.
• Cancer cells form disorganized clumps called tumors.
– Benign tumors remain clustered and can be removed.
– Malignant tumors metastasize, or break away, and can
form more tumors.
normal cell
cancer cell
bloodstream
5.3 Regulation of the Cell Cycle
• Carcinogens are substances known to promote cancer.
• Standard cancer treatments typically kill both cancerous
and healthy cells.
5.4 Asexual Reproduction
KEY CONCEPT
Many organisms reproduce by cell division.
5.4 Asexual Reproduction
Binary fission is similar in function to mitosis.
• Asexual reproduction is the creation of offspring from a
single parent.
– Binary fission produces two daughter cells genetically
identical to the parent cell.
– Binary fission occurs in
parent cell
prokaryotes (cells without a
nucleus).
DNA
duplicates
cell begins
to divide
daughter
cells
5.5 Multicellular Life
KEY CONCEPT
Cells work together to carry out complex functions.
5.5 Multicellular Life
Multicellular organisms depend on interactions among
different cell types.
CELL
TISSUE
leaf
stem
vascular
tissue
ORGAN
lateral
roots
primary
root
root system
• Tissues are groups of cells that perform
a similar function.
• Organs are groups of tissues that
perform a specific or related function.
• Organ systems are groups of organs
that carry out similar functions.
shoot system
SYSTEMS
5.5 Multicellular Life
Specialized cells perform specific functions.
• Cells develop into their mature forms through the process
of cell differentiation. Cells differ because of genes and
location in an embryo.
• Stem cells have the ability to
– divide and renew themselves
– remain undifferentiated in form
– develop into a variety of specialized cell types
Outer: skin cells
Middle: bone cells
Inner: intestines
5.5 Multicellular Life
• The use of stem cells offers many current and potential
benefits.
– Stem cells are used to treat leukemia and lymphoma.
– Stem cells may cure disease or replace damaged
organs.
– Stem cells may revolutionize the drug development
process.
5.5 Multicellular Life
KEY CONCEPT
Gametes (sex cells) have half the number of
chromosomes that body (somatic) cells have.
5.5 Multicellular Life
Your cells have autosomes and sex chromosomes.
• Your body cells have 23 pairs
of chromosomes; homologous
pairs of chromosomes have the
same structure; for each
homologous pair, one
chromosome comes from each
parent.
• Chromosome pairs 1-22 are
autosomes.
• Sex chromosomes, X and Y,
determine gender in mammals.
5.5 Multicellular Life
Body cells are diploid; gametes are haploid.
• Fertilization between egg and sperm occurs in sexual
reproduction.
• Diploid (2n) cells have two copies of every
chromosome.
– Body cells are diploid.
– Half the chromosomes come from each parent.
5.5 Multicellular Life
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– Gametes have 22 autosomes and 1 sex chromosome.
5.5 Multicellular Life
• Meiosis differs from mitosis in significant ways.
– Meiosis has two cell divisions while mitosis has one.
– In mitosis, homologous chromosomes never pair up.
– Meiosis results in haploid cells; mitosis results in diploid
cells.
5.5 Multicellular Life
KEY CONCEPT
Mendel’s research showed that traits are inherited as
distinct units.
5.5 Multicellular Life
Mendel laid the groundwork for genetics.
• Traits are distinguishing
characteristics that are
inherited.
• Genetics is the study of
biological inheritance patterns
and variation.
• Gregor Mendel showed that
traits are inherited as discrete
units.
• Many in Mendel’s day thought
traits were blended.
5.5 Multicellular Life
Mendel’s data revealed patterns of inheritance.
• Mendel made three key decisions in his experiments.
– use of purebred plants
– control over breeding
– observation of seven
“either-or” traits
5.5 Multicellular Life
• Mendel used pollen to fertilize selected pea plants.
– P generation crossed to produce F1 generation
– interrupted the self-pollination process by removing male
flower parts
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
5.5 Multicellular Life
• Mendel allowed the resulting plants to self-pollinate.
– Among the F1 generation, all plants had purple flowers
– F1 plants are all heterozygous (same gene type
expressed)
– Among the F2 generation, some plants had purple
flowers and some had white
5.5 Multicellular Life
The same gene can have many versions.
• A gene is a piece of DNA that directs a cell to make a
certain protein.
• Each gene has a locus, a
specific position on a pair of
homologous chromosomes.
5.5 Multicellular Life
• An allele is any alternative form of a gene occurring at a
specific locus on a chromosome.
– Each parent donates
one allele for every
gene.
– Homozygous
describes two alleles
that are the same at a
specific locus
(location on DNA).
– Heterozygous
describes two alleles
that are different at a
specific locus.
5.5 Multicellular Life
Genes influence the development of traits.
• All of an organism’s genetic material is called the genome.
• A genotype refers to the makeup of a specific set of genes.
• A phenotype is the physical expression of a trait.
5.5 Multicellular Life
• Alleles can be represented using letters.
– A dominant allele is
expressed as a phenotype
when at least one allele is
dominant.
– A recessive allele is
expressed as a phenotype
only when two copies are
present.
– Dominant alleles are
represented by uppercase
letters; recessive alleles by
lowercase letters.
5.5 Multicellular Life
Punnett squares illustrate genetic crosses.
• The Punnett square is a grid system for predicting all
possible genotypes resulting from a cross.
– The axes represent
the possible gametes
of each parent.
– The boxes show the
possible genotypes
of the offspring.
• The Punnett square
shows the possible
genotypes and
phenotypes. Usually
shown as a percentage
or fraction.
5.5 Multicellular Life
Heredity patterns can be calculated with probability.
• Probability is the likelihood that something will happen.
• Probability predicts an average number of occurrences, not
an exact number of occurrences.
number of ways a specific event can occur
• Probability =
number of total possible outcomes