life 120 exam 3

cell division purpose

it supports organism reproduction

asexual reproduction

in unicellular organisms, cellular division reproduces the entire organism

sexual reproduction

in multicellular organisms, cellular division creates germ cells that reproduce by combining with other germ cells

tissue growth in multicellular organisms

• division of a single cell can turn into multicellular tissues

• cell division allows damaged tissues to reform/be repaired

the big picture of cell division

• duplicate cell components

  • chromosomes

  • organelles

• separate material into two daughter cells

  • chromosomes

  • organelles

challenges of cell division

1. you need enough materials to create two different cells and those cells must be functional

2. you need to duplicate cell components, DNA copying and passing must have exquisite fidelity

3. you need to segregate cell components, including ribosomes and other organelles

4. you need to do this a billion times, and it must respond effectively to outside signals and timing events

genome

all of the cell’s information (DNA)

chromosome

a DNA double helix wrapped around proteins

chromatin

• substance that makes up eukaryotic cells

• consists of DNA and proteins

• each eukaryotic species has it’s own characteristic number of chromosomes

human genome

has 46 total chromomsomes

somatic cells

cells that aren’t involved in reproduction

• skin cells, brain cells, muscle cells, etc

• 46 chromosomes with 23 homologous pairs

germ cells

cells that are involved in reproduction

• eggs and sperm

• 23 chromosomes that come from each individual homologous pairs

karyotype

a display of the chromosomes in a cell

chromosome structure before division

prior to cell division, the entire chromosome replicates

duplicated chromosome

• has two identical copies of the same information

• condense prior to replication

• consists of sister chromatids that are joined by centromeres

cell division separates sister chromatids

interphase

• 90% of the cell cycle

• g1 (first gap): longest

• g0: cell division does not occur, cell leaves cell cycle

• s (synthesis: reduplication

• g2 (second gap): ready for duplication

mitotic phase

• 10% of cycle

• mitosis: nuclear division

• cytokinesis: cytoplasm division

g2 of interphase

• centrosomes have duplicated

• nuclear envelope surrounds the nucleus

• duplicated chromosomes have not yet condensed

prophase

• chromosomes and centrosomes have duplicated

• mitotic spindle forms, pushing the two centrosomes away from each other

• chromosomes condense, duplicated chromosomes appear to have two sister chromatids

prometaphase

• nuclear envelope starts to dissolve

• microtubules invade nuclear envelope area and attach to chromatids through kinetochores

• chromosomes are pulled back and forth by microtubules

• non-kinetochore microtubules interact with each other

metaphase

• chromosomes align in the middle in the metaphase plate

• centrosomes are at opposite ends of the cell

• microtubules are attached to the chromatids from opposite poles through kinetichores

anaphase

• sister chromatids are separated and are pulled to opposite poles

• cell begins to elongate as nonkinetochore microtubules lengthen

• two ends of the cell gain a full set of chromosomes

telophase/cytokinesis

• nuclear envelope reforms

• chromosomes become less condensed

• spindle depolymerizes

• cell membrane divides cytoplasm at cleavage furrow

mitotic spindle

• made up of microtubules and associated proteins

• controls chromosome movement during mitosis

• in animal cells, spindle microtubule assembly begins at the centrosomes

• microtubules reorganize to form the mitotic spindle and segregate chromosomes

microtubule structure

• narrow tubes that are made of tubulin proteins

• they are oriented

  • plus end and minus end

• they are dynamic

  • they grow by adding tubulin to the plus end

  • they shrink by losing tubulin from the minus end

• microtubule length is dictated by the adding and subtracting of subunits from each end

dyenin

moves to the minus end

kinesin

moves to the plus end

centrosome formation and movement

• prophase: microtubules elongate from centrosomes, push centrosomes apart

• prometaphase: centrosomes at opposite ends of cell, microtubules attach to chromosome kinetichores

centrosome

microtubule organizing centers, duplicate prior to cell division

chromosome movement

• prometaphase: microtubules pull chromosomes towards cell pole, movement opposed by pull from other pole

• metaphase: the chromosomes have been aligned along the metaphase plate

• anaphase: cohesion proteins are digested, allow sister chromatids to separate, pulled towards each pole

how do chromosomes pull apart?

• they are pulled apart by motor proteins through the mitotic spindle

• chromosomes can be “reeled in” by motor proteins that are anchored at the centrosome

• chromosomes can be “walked in” by motor proteins anchored at the chromosome

photobleaching experiment

1. microtubules are coupled to a fluorescent marker

2. a region of the microtubule is photobleached

cytokinesis is driven by:

actin-based cell body contraction

actin-based cell body contraction

1. actin forms long filaments

2. antiparallel myosin motors move these filaments

3. actin-myosin complexes make up contractile ring

4. myosin activity causes ring to contract, form cleavage furrow

cell division in bacteria

• prokaryotes reproduce through binary fission

• in e.coli, the single chromosome replicates, beginning at the origin of replication

• the two daughter chromosomes actively move apart while the cell elongates

• the plasma membrane pinches inward, dividing the cell

growth factors

• proteins released by other cells that stimulate cell growth

• PDGF

pdgf

released by platelets, stimulate fibroblast division and wound healing

density-dependent inhibition

cells in contact with other layers will stop dividing and create a monolayer

cell cycle control system

• the cell has a series of checkpoints where various signals determine whether a cell can proceed through the cell cycle

• these checkpoints register signals from inside and outside the cell

cancer

• results from unchecked cell division

• does not respond well to cell cycle checkpoints or control mechanisms

mitosis for homologous chromosomes

genetic inheritance

• genetic information is passed down from generation to generation

• key to natural selection

heredity

transmission of traits from one generation to another, genetic factors cause offspring to resemble their parents

variation

differences in appearance that offspring show from parents, siblings, and others

genetic information: more than appearances

• most characteristics of organisms are influenced by environmental and genetic factors

• affects outward appearances

• genetic factors regulate many different traits

  • homeostasis

  • performance

  • disease susceptibility

genes

units of heredity, represent a particular region of DNA

• genes are passed from one generation to the next as part of chromosomes

alleles

variants of a given gene, due to slight differences in DNA sequence

locus

the position of a gene within a chromosome

homologous chromosomes

• same size

• same banding pattern

• same genes in the same loci

• may have different alleles

• DNA sequences are nearly identical, but may have important differences that give rise to alleles

sex chromosomes

chromosomes that determine the genetic sex of an organism

• women = homologous pair of XX

• men = x and y chromosome

autosomes

the remaining 22 chromosomes

more about somatic cells

• one set from mother, one set from father

• each pair of homologous chromosomes include one chromosome from each parent

more about gametes

produced by germ cells in reproductive organs (ovaries and testes)

• each chromosome is either maternally or paternally derived

ploidy

number of sets of chromosomes

• n = number of chromosomes in single set

• humans: n = 23 chromosomes

diploid

having two sets of chromosomes

• human somatic cell: 2n = 46

haploid

one set of chromosomes

• gamete: n = 23

asexual reproduction

a single individual passes genes to its offspring without the fusion of gametes

clones

a group of genetically identical individuals

sexual reproduction

two individuals give rise to offspring that have unique combinations of genes inherited from the two parents

life cycle

the generation-to-generation sequence of stages in the reproductive history of an organism

human life cycle

• multicellular diploid adults produce haploid gametes in reproductive organs by meiosis

• resulting sperm and egg cells have one chromosome from each homologous pair

• haploid gametes fuse during fertilization, creating a zygote

• the zygote produces somatic cells by mitosis, develops a mature organism

zygote

resulting fertilized egg, contains one set of chromosomes from each parent

alternation of generations life cycle

• includes multicellular diploid and haploid stages

  • plants and algae

• sporophyte: diploid organism that creates haploid spores through meiosis

• each spore grows by mitosis and creates a haploid organism called the gametophyte

• gametophyte: make haploid gametes by mitosis

• fertilization of gametes results in a diploid sporophyte, which grows by mitosis into multicellular sporophyte

meiosis

• preceded by replication of chromosomes like mitosis

• takes place in two sets of cell divisions: meiosis i and ii

• two cell divisions result in four daughter cells

• each daughter cell has only half as many chromosomes as the parent cell

meiotic divisions

• first meiotic division: homologous pairs of chromosomes pair and separate

• second meiotic division: sister chromatids of each chromosome separate

• four new haploid cells are produced as a result

independent assortment of chromosomes

• homologous pairs are oriented randomly during metaphase i of meiosis

• homologous pairs sort maternal and paternal homologs into daughter cells independently of other pairs

• the number of combinations possible when chromosomes assort independently into games is 2^n, where n is the haploid number

• for humans, there are more than 8 million (2²³) possible combinations of chromosomes for gametes

crossing over

• produces recombinant chromosomes, which combine DNA inherited from each parent

• begins very early in prophase i

• homologous portions of two nonsister chromatids trade places

• crossing over contributes to genetic variation by combining DNA, producing chromosomes with new combos of maternal and paternal alleles

random fertilization

adds to genetic variation because any sperm can fuse with any ovum

• fusion of two gametes produces a zygote with any of about 70 trillion diploid combinations

character

heritable feature that varies among individuals

trait

variant of a particular character

blending hypothesis

initial ideas on genetic inheritance were that genetic material tended to blend during successive generations

particulate hypothesis

parents pass on discrete heritable units (genes) that remain intact across generations

model organisms

non-human species that is studied to understand basic biological processes

benefits of snow peas

• they have many characters with traits that are visually discernable

• they can be grown in large enough numbers that overall patterns can be determined by statistics

• matings can be controlled between plants

snow peas normally ______

self-fertilize

controlled matings

1) remove stamens from purple flowers

2) transfer sperm-bearing pollen from stamens of another flower

3) pollinated carpel matures into a pea pod

4) plant seeds fro pods

5) offspring develop

keys to mendel’s experimental design

• chose to study only characters that occured in two distinct alternative forms

• used plants that were true-breeding for many generations

• tracked plants through three generations

true breeding

produce offspring with the same trait when they self-pollinate

mendel’s mating strategy

• cross 1: hybridization = mated two contrasting, true breeding plants

  • true breeding parents are the p generation

  • hybrid offspring of the p generation are called the f1 generation

• cross 2: allows f1 individuals to self-pollinate or cross pollinate with other f1 hybrids

  • offspring of the f1 generation are the f2 generation

mendel’s model of genetic inheritance

1) alternative versions of genes account fr variations in inherited characters

2) for each character, an organism inherits two alleles, one from each parent

3) if the two alleles at a locus differ, then one (dominant) determines the organism’s appearance, and the other (recessive) has no noticeable effect on appearance

4) the two alleles for a heritable character separate during game formation and end up in different gametes

1) alternative versions of genes account fr variations in inherited characters

• alleles

• each gene resides at a specific locus on a chromosome

2) for each character, an organism inherits two alleles, one from each parent

• mendel made this deduction without knowing th existence of chromosomes

• two alleles at a particular locus may be identical, p1 generation

• two alleles at a particular locus may differ, f1 generation

4) the two alleles for a heritable character separate during game formation and end up in different gametes

• law of segregation

• an egg or sperm gets only one of the two alleles

• segregation of alleles corresponds to distribution of homologs to different gametes in meiosis

phenotype

organism’s physical makeup

• beacuse of dominant and recessive allels, an organism’s traits don’t always reveal genetic composition

genotype

organism’s genetic makeup

homozygous

having two identical alleles for a gene

heterozygous

having two different alleles for a gene

punnet squares

1) different possible gametes are placed on each axis

2) potential fertilization events are represented by gamete combinations in the center squares

3) genotypes for each offspring converted to phenotypes

testcross

used to determine genotype of individual w/ dominant phenotype

• cross with homozygous recessive

• if any offspring display recessive phenotype, then original must have been heterozygous

p generation

consists of plants that are true-breeding for both characters

f1 generation

will be heterozygous for both genes

law of independent assortment

states that each pair of alelles segregates independently of each other pair of alleles during gamete formation

• applies to genes on different chromsomes or those far apart on the same chromosome

• genes located near each other on the same chromosome are inherited together

genetic inheritance and probability

mendel’s law of segregation and independent assortment reflect the rules of probability

mutliplication rule

probaiblity of two or more independent events occur together due to the product of their individual probabilities

addition rule

probaiblity that two or more mutually exclusive events will occur

beyond mendelian genetics

• not all heritable characters are determined as simply as the traits mendel studies

• basic principles of segregation and independent assortment still apply ot the inheritance of chromosomes/genes for complex characters

• these genes have more complicated ways of expressing phenotype instead of dominant-recessive relationships

incomplete dominance

the phenotype of the heterozygote is between homozygote recessive and dominant

• due to the biochemical actions of the underlying alleles/proteins

codominance

two dominant alleles affect the phenotype in separate, distinguishable ways

multiple alleles/blood type

• most genes have more than two alleles in nature

• blood type: a, b, ab, o

• three blood alleles: a, b, o

• alleles code for different enzymes that adds carbohydrates to the surface of blood cells

• the enzyme encoded a adds a carb, enzyme for b adds b card, enzyme for o adds neither