MCB Exam 3

gene- vs gene+

mutation vs wild-type

do chemicals, radiation or uncorrected mistakes in replication account for the most mistakes?

uncorrected mistakes in replication

how often do errors occur in E coli?

4 mutations/100 cell divisions

how often do errors occur in humans?

1/billion - 6 per cell cycle

how many mistakes does e coli make per cell division in vitro (test tube)?

400

what proofreads DNA?

3’-5’ exonuclease activity - accounts for half of reduction in error frequency

where does new DNA get methylated?

the adenine in 5’-GATC-3’

mismatch repair system

looks for hemimethylated DNA - 1 strand methylated, 1 not

MutS

scans DNA for mismatches

MutL

bridge between detection and repair

MutH

cuts unmethylated strand

what fills in the cut out gap of DNA in the mismatch repair system?

DNA polymerase III

what closes the final nick in the newly put in strand of DNA in the mismatch repair system?

DNA ligase

what does mismatch repair require?

free 3’-OH group

transition base substitution

say in family

transversion base substitution

pyrimidine ←> purine

same sense mutation

redundancy

missense mutation

codes for different amino acid

nonsense mutation

changes to a stop codon

what causes sickle-cell anemia?

substitution in B-globin subunit

phenylketonuria

causes severe mental impairment; managed with special diet

phenylketonuria cause

can’t metabolize phenylalanine

cystic fibrosis cause

removal of one amino acid from sequence

leukemia/lymphoma cause

translocation

muscular dystrophy cause

deletion

haemophilia A cause

insertion

fragile X syndrom and Huntington’s cause

duplication of short sequences

what activates oncogenes to cause cancers?

duplication

actin monomers

highly folded, globular proteins

G actin

43 kDa protein, 375 amino acids

G actin characteristics

has nucleotide binding site for ATP + ADP; has polarity (directionality); highly conserved; abundant

pointed vs barbed ends of actin

pointed - minus, barbed - plus

what direction to actin monomers polymerize?

head to tail

what does polymerization begin with?

nucleation (cluster of monomers come together)

F actin

microfilament of many G actin

which end of F actin has more polymerization?

plus end

does ATP or ADP have a high affinity for other actin?

ATP

monomer binding proteins

hide actin - bind to G actin to prevent it from polymerizing into F actin

microvilli

actin filaments x bundling proteins; minus ends anchored to actin network

actin networks

provide structural stability, more flexible than bundles

myosin

converts ATP into mechanical energy

filament sliding

myosin fused together (don’t move themselves) and pull filaments together

movement of myosin along actin microfilament

1. bind ATP → let go

2. ATP hydrolysis → move head group

3. attach w/ADP group → eject phosphate → power stroke → OG position

myofibril

many sacromeres

muscle fiber

many myofibrils

what are actin/myosin combos used for?

cytokinesis, cell crawling, vesicle transport, contraction

what are microtubules used for?

interphase - guide intracellular transport, dividing - segregate chromosomes, ciliated cells - propulsion

microtubules

rigid, hollow tubes of tubulin

tubulin

dimer of a-tubulin and B-tubulin

what do a-tubulins and B-tubulins bind respectively?

GTP and GDP

tubulin dimers polymerize to form microtubules

13 linear “protofilaments" - polymerization mostly at + end

what happens shortly after a dimer addition to a microtubule?

GTP in B-tubulin hydrolyzed → weakens affinity for other tubulin (GTP cap)

what do binding tubulin drugs do?

induce depolymerization

binding tubulin drugs, non-specifically affects all microtubules

colchicine + colcemid

binding tubulin drugs, affect rapidly dividing cells

vincristine + vinblastine

what do binding microtubules drugs do?

stabilize microtubules

binding microtubule drug, targets rapidly-dividing cells

taxol

where do new microtubules come from?

microtubule organizing center (MTOC)

where is the major MTOC in animal cells?

the centrosome - minus ends anchored in centrosome

centrioles arrangement

27 microtubules - 9 triplets

what does gamma tubulin do?

facilitates making of new microtubules on a pre-formed platform

pericentriolar material (PCM)

amorphous collection of proteins from which microtubules originate

where do microtubules originate?

the centrosome

stable microtubules

provide polarity

associated motor proteins

kinesin and dynein

kinesin

long pair, walks to plus end

dynein

go to minus end

microtubules and motor proteins functions

• intracellular vesicle transport

• organelle movement

• color changes

• bending

• separation of sister chromatids and centrosomes during

  M-phase

axoneme arrangement

9 + 2 - 9 doublets, 2 independent in middle

axoneme

microtubule; central strand of cilia or flagella; only dyneins

where are minus ends of axonemes anchored?

basal body

axonemal dynein movement

walks towards minus end, pulls towards plus end

M phase and interphase percentages

M - 5%, interphase - 95%

when is the nucleus disassembled in the cell cycle?

late prophase

when is the nucleus reassembled in the cell cycle?

telophase

what binds to nuclear membrane vesicles after disassembly?

Lamin B

what do vesicles bind to in order to reassemble the nucles?

chromosomes

kinetochores

protein complexes on centromere of chromatid that attach to spindle microtubules

Anaphase A

movement of sister chromatids to opposite poles via kinetochores

Anaphase B

spindles distance, further separating sister chromatids

polar vs astral microtubules in anaphase B

polar - push, astral - pull

prometaphase

kinetochore microtubules move pairs of sister chromatids until they reach the metaphase place

co-translational sorting

translated on membrane bound ribosome

post-translational sorting

fully translated then sorted

where do polypeptides go with co-translational sorting?

remain in ER or go to golgi complex → secretory vesicles, lysosomes, plasma membrane

where do polypeptides go with post-translational sorting?

remain in cytosol or imported into organelle

nuclear pore complex

never fully closes - small molecules <20 kDa use passive diffusion

nuclear localization signal (NLS)

amino acid sequence that lets cytoplasmic proteins into nucleus

NLS is rich in…

basic amino acids (positive)

nuclear export signal (NES)

keeps nuclear proteins out of cytoplasm

NES is rich in…

leucine

NLS process

1. importins recognize and hold onto NLS

2. pass through nuclear pore complex

3. bind RanGTP to let go of NLS → RanGDP outside

NES process

1. exportins recognize and hold onto NES with RanGTP

2. pass into cytoplasm

3. GTP hydrolysis converts RanGTP to RanGDP → lets go of both

RanGTP role for NLS vs NES

importin - can’t bind NLS w/RanGTP

exportin - only binds NES w/RanGTP

cristae

sacs of inner membrane joined to rest of inner membrane by short tubes

human mitochondrial genome

16.5 kbases DNA

how many protein-coding genes are for the electron transport chain?

13

are most mitochondrial genes coded for by genes on the mitochondrial genome?

no

mitochondria electrochemical gradient

positive cytosol and intermembrane space, negative matrix