Bio Quiz 2

cell cycle

regulation of cell behavior to ensure proper function of tissue/organ/organism, dysregulation leads to uncontrolled cell growth

purpose of the cell cycle

division (mitosis), growth and replicating DNA, apoptosis (cell death), development, generation, cells perform tissue specific functions

information that influences cell outcomes

genetic (DNA) and environmental

DNA compaction order

double helix—histone—nucleosome—chromatin—chromosome

histone

protein that DNA is wrapped around

nucleosome

DNA + loop

chromatin

fiber in which nucleosome (DNA + loop) is packaged

chromosome

a structure containing genetic information in the form of genes, (protein + DNA + RNA), forms around time cell divides

sister chromatids

two attached, double-stranded DNA copies of a replicated chromosome. seperate during mitosis and become independent chromosomes

what is necessary for cell division

protein synthesis, organelle production, increased volume of cytoplasm, replicate DNA

interphase

G1, S, G2, prepares cell for cell division

G1 phase

growth phase, cell enters immediately after dividing, chromosome unwinds and uncoils

S

replication phase

G2

prepares cell for cell division by making sure it contains enough proteins and organelles, protein synthesis and organelle production continues

at the end of G2

cell checks for MPF (mitosis promoting factor) protein. if concentration is high, cell exists interphase and enters mitosis

G0

resting phase, comes to this phase if the cell fails G1 checkpoint or doesn’t need to divide, nerve cells and muscle cells spend all of its time here

M phase

mitosis, process by which the cell divides into two identical daughter cells, PMAT

mitosis

division of the cell’s nucleus

cytokinesis

division of the cytoplasm

cell cycle 2 main phases

interphase and cell division (mitosis)

chromosome segregation

two sister chromatids formed, separate from each other and migrate to opposite poles of nucleus, occurs in mitosis, 1 trait

meselsohn-stahl experiment 1

e coli bacteria cells were grown in a medium rich in heavy nitrogen (N-15) to produce radioactively labeled DNA molecules (cell have N-15 in their DNA)

meselsohn-stahl experiment 2

e coli bacteria cells were transferred into a medium with regular N-14 atoms

messelsohn-stahl experiment 3 (key question)

what is the distribution of N-14 and N-15 after consecutive cycles of replication? this question determines if DNA is semi-conserved or not

messelsohn-stahl experiment 4

original parental strands contain N-15 isotopes, replicated daughter strands contained N—14 isotopes, DNA with different densities can be separated by centrifugation

messelsohn-stahl experiment 5

after centrifugation, 3 photographs described band that correlates to DNA molecule that was extracted

density shifts generation after generation, showing DNA is semi-conserved

semi-conservative

1 original strand, 1 new strand, each strand acts as a template for synthesis of a new strand

conservative

original pair, completely new pair

dispersive

2 pairs with old and new DNA dispersed within the DNA

helicase

“unzipping enzyme”, breaks hydrogen bond holding bases together

single-strand DNA-binding proteins

keeps DNA strands separated when unzipped

topoisomerase (DNA gyrase)

keeps DNA from supercoiling by removing the stress caused by unwinding, cuts and reseals DNA

primase

“the initializer”, binds to each one of DNA strands, adds a set of nucleotides (RNA primer) that acts as a signal for DNA polymerase to know where to start to work

dna polymerase III

binds to primer region and adds individual nucleotides 1 by 1 (attaches nucleotides together via phosphodiester bonds), extending synthesized strand (daughter strand)

can only builder new strand in 5’ to 3’ direction

sliding clamp

holds DNA polymerase in place during strand extension

DNA polymerase I

removes RNA and replaces it with DNA, can only build new strand in 5’ to 3’ direction

DNA ligase

“the gluer”, helps “glue” DNA fragments together, seals gap between Okazaki fragments via phosphodiester bonds

DNA replication

synthesizing new strand of DNA from original strand, occurs in nucleus, done before cell divides (mitosis/meiosis)

leading strand

elongates towards the replication fork, synthesized continuously

lagging strand

elongates away from the replication fork, synthesized discontinuously

Okazaki fragment

short sequences of DNA nucleotides synthesized discontinuously and linked together

replication fork

point where unwinding is taking place (can move)

replication origin

a sequence of nucleotides where DNA starts/is initiated

proofreading and mismatch repair

DNA polymerase proofreads the base that has just been added, checks where base pairing it correct

if incorrect base was added: new DNA strand is cut and mispaired nucleotide and its neighbors are removed

DNA polymerase replaces it with correct nucleotides, DNA ligase (glue) seals the gap, increase fidelity (accuracy)

mutation

uncorrected mistakes lead to ___

prophase

DNA condenses from chromatin to chromosomes, 2 centrioles begin to move to opposite ends and synthesize spindles

pro metaphase

nuclear membrane break down allows for spindle attachment to a special region on the centromere, kinetochores (attachment points)

metaphase

centrioles are at opposite ends, spindle fiber attaches to kinetochore and pulls chromosome to the center of the cell (aligns the on the equatorial line)

anaphase

disjunction - separation of chromosomes, spindle fibers pull sister chromatids apart by breaking centromeres and moving chromatids to opposite ends

telophase

nuclear membrane and nucleolus reforms at teach end, spindle begins to deteriorate, chromosomes uncoil and decondense into chromatin

cytokinesis

breaking of the cytoplasm, organelles are distributed among 2 cells, chromosomes have decondensed

chromatin condensation (photo)

-

spindles

protein fibers made from microtubules that are dissasebled into subunits, leading to chromosomal movement

centromeres

holds sister chromatids together

kinetochores

disk shaped proteins on chromatids, spindle fibers attach to it, dissembles microtubules

how does kinetochore dissemble microtubules

motor protein walks kinetochore along microtubules disassembling it into subunits as it passes

microtubules are shortened by disassembly rather than contraction or movement

centrosome

each animal cell has 1, region of the cell that contains 2 identical centrioles

centrioles

synthesize spindle apparatus

experimental evidence of cell cycle control

when a cell in M phase was fused with one in interphase, the nucleus of the interphase cell immediately initiated mitosis, even if its chromosomes had not replicated

general control mechanism

timer, correct sequential initiation of events, binary on/off switches, backup mechanisms, sensors

checkpoints act through ____ signals and are/are not essential for cell progression

negative signals (“who isn’t ready”), are not essential

M-phase promoting factor

combination of cyclin and cdk (cyclin dependent kinase)

protein kinases

enzymes that transfer a phosphate group (usually ATP) onto a target protein, changing protein function from inactive to active

cyclin dependent kinase

catalyzes phosphorylation of other proteins to start M phase, can only phosphorylate proteins when it is bounded with partner cyclin, allosteric activation

cyclins

one of several regulator proteins whose concentrations fluctuate (proteins undergo a cycle of synthesis and degradation) throughout the cell cycle

phosphorylation leads to …

protein being activated, protein being deactivated, or a transferred phosphate group acting as a signal to other proteins to interact with the target protein

ki

kinetic = to move = kinase move

MPF Component Concentration Graph

-

if cyclin is high and cdk is active

cell cycle is on

if cyclin is low/cdk is inactive

cell cycle is off

G1 checkpoint

cell size is adequate, nutrients are sufficient, social signals are present, dna is undamaged

G2 checkpoint

chromosomes replicated successfully, activated MPF is present, dna is undamaged

M checkpoint (metaphase to anaphase)

ensures sister chromatids do not split until all kinetochores are attached properly to the spindle apparatus

M checkpoint (anaphase to telophase)

cells must degrade all of their cyclin and thus turn off MPF activity

enzymes responsible for degrading cyclin are only activated when all the chromosomes have been properly seperated

purpose of all 4 checkpoints

prevent the division of cells that are damaged or that have other problems

what happens if cell cycle checkpoints fail

accumulation of DNA damage, uncontrolled cell growth, genomic instability, loss of apoptosis control, development of genetic disorders

cancer

cells that grow in an uncontrolled fashion, invade nearby tissues, spread to other sites in the body

cancerous cells use nutrients and space needed by normal cells and disrupt function of normal tissues

1st defect cancerous cells have related to cell division

defects that activate proteins required for cell growth when they shouldn’t be active, G1 cyclin is overproduced

2nd defect cancerous cells have related to cell division

defects that prevent tumor suppressor genes from shutting down the cell cycle, p53 (tumor suppressor protein that helps regulate progression) is defective or inactive

malignant tumor

tumor that is actively growing and disrupting local tissues or spreading to other organs

benign tumor

mass of abnormal tissue that develops due to unregulated growth but does not spread to other organs

social control

cells divide in response to signals from other cells, individual cells are allowed to divide when it is in the best interest of the organism as a whole

social control and cancer

normal social controls on G1 checkpoint breakdown in cancerous cells, cells divide in absence of go-ahead signal from growth factors

due to “defect cancerous cells have related to cell division”

p53

tumor suppressant protein, responds to DNA damage and prevents the formation of tumors consequently regulation cell cycle progression, “checkpoint”

p53 abilities

trigger DNA repair, stop cell division, activate apoptosis

p21

an inhibitor of s phase cycling

p53 (1)

p53 is inactive when binded to mdm2

p53 (2)

DNA damage causes phosphorylation of p53

p53 (3)

p53 is phosphorylated and active, mdm2 is removed

p53 (4)

increases the activity of the gene responsible for making p21 protein, “booster that encourages cell to produce more p21”

p53 (5)

p21 binds to cdk2-cylcin complexes and inhbits their activity, leading to cell growth arrest

purpose of meiosis

produce 4 genetically different haploid(n) cells

homologous chromosomes

approximate the same size, same shape, and contain same types of genes in the same locations

gametes

egg or sperm

somatic cells

any cells other than reproductive cells

haploid

(n), having one set of chromosomes

diploid

(2n), having two sets of chromosomes

zygote

cell formed by union of two gametes (an egg and sperm)

karyotype

distinctive appearance of all metaphase or pro metaphase chromosomes, including # of chromosomes, length, and their banding patterns

recombination (crossing over)

exchange of genetic information between non-sister chromatids of homologous chromosomes, produces 2 new recombinant chromosomes