biology 302 exam 4

what is the “genetic” approach to studying a biological problem?

look for mutants in which the process is defective

what is spontaneous?

uncorrected errors in DNA replication and natural mutagens (xrays, gamma rays, UV light)

what is induced?

expose population to mutagen

what is the genetic approach to understand a process?

1. do mutagenesis


1. perform a mutant “screen”

what is mutagenesis?

expose a population to mutagen

what is mutant screen?

look for mutants that have a phenotype affecting the process of interest

what did beadle and tatum do?

a genetic screen for neurospora mutants which had defects in biochemical pathways for making vitamins and amino acids

what is the plan of beadle and tatum’s experiment?

isolate auxotrophic mutants which can’t make specific vitamins or amino acids

what happens if you expose the haploid spores to a mutagen?

it introduces random mutations in the genes

where can wild type e.coli grow?

on plates containing only lactose

what are lac- mutants?

auxotrophic mutants that were unable to grow with lactose as an energy source

what are lacc mutants?

mutants that expressed the lac operon genes constitutively, even in the absence of lactose

what are lacl^s mutants? (superrepressor)

mutants that never expressed the lac operon genes, even in the presence of lactose

what is the 1st step of genetics to study a biological process?

genetic method in the single cell eukaryote yeast to understand regulation of the cell cycle

what is the 2nd step of genetics to study a biological process?

genetic method in the plant to understand control of flower development

what is the 3rd step of genetics to study a biological process?

genetic method in the nematode roundworm to understand control of cell fate specification during animal development

why do geneticists use brewer’s yeast to study basic processes that occur in eukaryotes?

• single celled

• basic cellular processes are the same as more complex, multicellular animals

• fewer genes than in multicellular

what happens during a mitotic cell cycle?

1 cell divides into 2 → mother cell budding off a new daughter cell

what did hartwell do to study the eukaryotic cell cycle?

mutagenized yeast, then screened temp-sensitive mutants that couldn’t complete the cycle

• grow the mutagenized cells at 23°

• make a copy of the plate

• shift 1 copy to 36°

• look for colony that grows on 23°; not 36°

what was the end product of hartwell’s experiment?

dozens of temp-sensitive mutant strains w/ a mutation in each strain

what did hartwell call the temp-sensitive mutant strains?

cdc genes = cell division cycle mutant

what was the conclusion of hartwell’s experiment?

the mutated gene makes a protein required to proceed thru that specific step in the cell cycle

what did they find out about cdc genes?

conserved in eukaryotes, and controlled the cell cycle in other species

what are homologous genes/homologs?

a gene present in 2 species b/c of descent from a common ancestor

what is the ‘model system’ approach?

taking the genetic approach to study a process in a simpler species can yield results relevant to other species

why does the model system approach work?

because genes are conserved and perform the same/similar functions in different species

where do stem and branches grow from?

shoot meristem

where do roots grow from?

root meristem

where do flowers grow from?

inflorescence (flower) meristem

how is the flower in Arabidopsis thaliana organized?

4 whorls

what is whorl 1?

sepal

what is whorl 2?

petal

what is whorl 3?

stamen = makes male gametes (pollen)

what is whorl 4?

carpel = makes female gametes (ovule)

what did elliot meyerowitz at the caltech lab do?

mutant screen and identified mutants in which flowers developed incorrectly

what did elliot meyerowitz screen in the Arabidopsis thaliana flower experiment?

mutants in which the wild type flower structure was not made

what are the 3 classes of the Arabidopsis thaliana flower mutants?

1. no sepals/petals

2. no petals/stamens

3. no stamens/carpels

what does the wild type of the Arabidopsis thaliana flower look like?

what did elliot meyerowitz hypothesize?

whorl identity is controlled by the combination of genes expressed in that whorl

what does whorl 1 do?

has class A genes - tells cells to form sepal

what does whorl 2 do?

has A + B genes - tells cells to form petal

what does whorl 3 do?

has B + C genes - tells cells to become stamen

what does whorl 4 do?

has C genes - tells cells to become carpel

whorl identity model

when the genes are identified, what did the transcription factors encode in the flower experiment?

express where the model predicted, combine with each other in pairs, regress each other’s expression, regulate downstream targets to specify organ made

where do all complex, multicellular organisms develop from?

a single cell; fertilized egg

what is undifferentiated?

has not adopted a distinct cell fate

what are cell intrinsic factors?

traits that are “intrinsic” to a person rather than being determined by that person's environment

what is extracellular signaling?

\
cues designed to transmit specific information to target cells

what are the vulva precursor cells (VPCs)?

cells in the skin of the animal (hypodermis)

where do VPCs sit?

underneath the anchor cell (AC) → cell in the gonad

are the VPCs born knowing their fate or are they instructed?

VPCs born not knowing what fate to adopt, anchor cell must tell them to adopt the 1° and 2° fates

what causes cells to adopt the vulva fates?

activation of the RAS pathway

what is cancer?

uncontrolled and inappropriate growth of cells

what is a benign tumor?

tumor that remains in the spot where it grew; usually not dangerous unless it presses on other organs

what is a malignant tumor?

a tumor that can invade surrounding tissue and spread

what is a metastatic tumor?

a second tumor caused when cells from the primary tumor move thru the body to colonize a new site

what is cancer a group of?

disorders characterized by the overgrowth of cells in different organs/tissues of the body

what are some common properties of cancer cells?

• evading apoptosis

• self-sufficiency in growth signals

• insensitivity to anti-growth signals

• sustained angiogenesis

• tissue invasion and metastasis

• limitless replicative potential

how do cancer cells divide?

uncontrollably

what are growth factors?

proteins secreted by cells that cause other cells to divide by ‘pushing’ them into the cell cycle

* bind receptors on the cell surface

what happens when the growth factors bind?

it activates signaling pathways that turn on expression of genes that instruct the cell to move thru the cell cycle and divide

do cells need growth factors?

no

what is apoptosis?

a damaged cell commits suicide by an orderly destruction of the cell (without causing an inflammatory response)

what do cancer cells display?

transformed phenotype in tissues

what is angiogenesis?

formation of blood vessels

what is tumor angiogenesis?

cancer cells can recruit blood vessels to themselves, allowing a tumor to grow beyond a certain small size

what happens if cancer cells move away from their site of origin?

they enter the bloodstream and move to a new site in the body

what type of disease is cancer in humans?

genetic

what percent of the time is the cancer sporadic?

90%w

what percent of the time is the cancer hereditary?

10%

what is clonal?

all cells in the tumor are progeny of 1 cell

what is the ‘multi-hit model’ for carcinogenesis?

cells becoming cancerous is a rare event that only happens after a number of key genes have been mutated in the same cell

what are oncogenes?

genes in which gain-of-function mutations contribute to cancer

what manner do oncogenes act in?

dominant

how many mutated copies does oncogenes need?

one

what are proto-oncogenes?

normal genes

what is Ras/GTPase?

protein found on the inside of the plasma membrane

what is the function of Ras/GTPase?

acts as a switch

* GDP bound, it is off
* GTP bound, it is on

what are tumor suppressor genes?

genes in which loss-of-function mutations contribute to cancer in a recessive manner

what is the cell cycle checkpoint?

a point in the cell cycle in which the state of the DNA or chromosomes is checked, and if it is not correct, then the transition to the next stage doesn’t happen

where is damaged DNA checked for?

• G1/S

• S phase

  • G2/M

what is p53?

a transcription factor protein that turns on the expression of many genes

what is the Mdm2 protein?

it exports p53 from the nucleus into the cytoplasm, where it is destroyed

what happens when damaged dna is detected?

p53 senses the damaged dna, p53 is not destroyed and moves into the nucleus to turn on genes:

• genes that cause the cell cycle to arrest

• genes that encode dna repair enzymes

what does p53 turn on if damage is really bad?

genes that cause apoptosis

what happens with a loss of p53?

eliminates the dna damage cell cycle checkpoints

what kind of mutations are in the BRCA1 and BRCA2?

germline mutations

what does mutations in BRCA1 and BRCA2 predispose a person to?

breast and ovarian cancer

what are the percentages for breast cancer?

• 12% of women will develop breast cancer at some time in their lives

• 60% of women who inherit the BRCA1 mutation will, by age 70

• 55% of women who inherit the BRCA2 mutation will, by age 70

what are the percentages for overian cancer?

• 1% of women will develop ovarian cancer at some time in their lives

• 60% of women who inherit the BRCA1 mutation will, by age 70

• 15% of women who inherit the BRCA2 mutation will, by age 70

what is the hayflick limit?

normal cells, when placed in tissue culture, can divide their dna about 50 times

what is replicative senescence?

normal cells are unable to divide after the hayflick limit

why does replicative senescence occur?

there is no expression of telomerase gene in most differentiated cells, and telomere ends degrade

how do cancer cells bypass replicate senescence?

they turn expression of telomerase back on = immortal

what is biotechnology?

the field of applied biology in which living organisms, or processes from living organisms, are used, usually w/ human modification, to serve some some scientific or medical purpose

genetic engineering

methods that rely heavily on knowledge from basic research into the genetics and molecular biology of model organisms

what is a genetically-modified organism?

an organism which has had its genome modified in some way by human intervention

what is the first reason for GMOs?

to make large quantities of a protein or drug in bacteria, animals, or plants

what is humulin?

human insulin made in bacteria