ch 5-7

Question 1

components of translation

Answer 1

mRNA (processed w 5’ cap, poly A tail, removed introns)
transfer RNA (3 double stranded loops, one single stranded, anticodon, anticodon loop and acceptor stem)
ribosomes (proteins and rRNAs structure in cytoplasm, big and small subunits of proteins and rRNAs, binding site for mRNA and three for tRNA)
translation factors

Question 2

what enzyme, in translation, helps attach the amino acids

Answer 2

aminoacyl tRNA synthetase

Question 3

initiation:

Answer 3

• initiation factors gather ribosome subunits, mRNA, initiator tRNA
• ribosome moves along mRNA until if finds AUG start codon
• tRNA w methionine binds
• ribosome has three spots: P, A, E

Question 4

initiation: P

Answer 4

(peptide): growing polypeptide, where initiator tRNA binds

Question 5

initiation: A

Answer 5

(amino acid): tRNA w next amino acid

Question 6

initiation: E

Answer 6

(exit): uncharged tRNA without amino acid is rejected

Question 7

elongation

Answer 7

• elongation factors let anticodons bind to codons
  4 steps repeat:
• tRNA in P site, next aa tRNA enters A
• polypeptide chain shifts to new aa in A, peptide bond between aas
• chain one aa longer
• mRNA moves forward one codon, tRNA w polypep at P, tRNA w/o aa exits at E, new codon at A ready for next tRNA

Question 8

termination

Answer 8

• stop codon on mRNA is reached
• release factor cleaves polypep from last tRNA
• ribosome splits and is recycled w mRNA

Question 9

post transcriptional modification: capping

Answer 9

• 5’ cap w 7-methyl guanosine added
• protects mRNA from digestion and helps initiate translation

Question 10

post transcriptional modification: tailing

Answer 10

• attaches to poly A tail to 3’ end
• made of 200-300 adenine ribonucleotides from poly A polymerase
• protects from degradation (…)

Question 11

post transcriptional modification: removal of non coding regions

Answer 11

exons: coding, interrupted by:
- introns: non coding, only in euk
- spliceosomes and small nuclear ribonucleoprotejns
introns are removed from pre mRNA, exons joined together to form mature RNA

Question 12

alternative splicing

Answer 12

produces different mRNAs from pre mRNA, lets 2+ polypeptides be made from a single gene
- after final mRNA is produced, it can leave nucleus to be translated
- after primary transcript is CAPPED, TAILED, SPLICED, it is an mRNA transcript

Question 13

mutation

Answer 13

permanent change in nucleotide sequence of DNA
- can be spontaneous or mutagen (chemicals, radiation) induced
- negative: genetic disorders
- positive: improved survival and reproduction (natural selection)
- neutral: most, since most DNA is non coding (introns are 90%)

Question 14

point mutations

Answer 14

single base change, pair base substitution
- silent mutation (no aa change, code redundancy)
- missense (change aa)
- nonsense (premature stop)

Question 15

sickle cell anemia

Answer 15

primarily africans
- recessive cell pattern
- 1/400 african americans

Question 16

frameshift mutations

Answer 16

• shift in the reading frame (changes everything downstream)
• insertions (adding bases)
• deletions (losing bases)

Question 17

chromosome mutations

Answer 17

involve large DNA segments
- deletion (of large coding region)
- duplication (of large coding region)
- inversions (chromosome segment is broken, re inserted in opposite direction)
- translocations (entire gene/group moved from one chromosome to another)

Question 18

spontaneous mutations

Answer 18

naturally in cell from normal interactions
e.g.:
- incorrect base pairing by polymerase
- dna transposition: transposons move freely and when near existing gene sequences, can alter gene expression

Question 19

prokaryotic metabolism

Answer 19

need to respond quickly to environmental changes
- enough of a product = stop production (waste of energy to produce more)
- new energy source: utilize quickly (start production of enzymes for digestion)

Question 20

natural selection favours the bacterial cells that can

Answer 20

metabolize well

Question 21

cells vary the amount of specific enzymes by

Answer 21

regulating gene transcription

Question 22

operon :

Answer 22

region in prokaryotes where many genes are clustered together under the control of a single promoter
- all genes transcribed into one continuous mRNA strand: polycistronic mRNA
- consists of coding region (genes) and regulatory region (promoter and operator)
- PROG (promoter, repressor, operator, genes)

Question 23

operons: PROG

Answer 23

• promoter (dna sequence where polymerase binds and begins transcription)
• repressor (protein binds to operator, prevents transcription)
• operator (regulatory dna sequence to which a protein binds, inhibits transcription initiation)
• genes

Question 24

lac operon

Answer 24

breaks down lactose in prokaryotes

Question 25

lac operon: presence of lactose

Answer 25

- lactose (inducer) binds to repressor so it can’t bind to operator, polymerase makes mRNA, mRNA makes enzymes that break down lactose - lac 1 protein: repressor, blocks transcription of b-galactosidase by binding to lactose operator - CAP binding site: dna sequence wher specific catabolism activator proteins bind to increase transcription rate

Question 26

lac operon: absence of lactose

Answer 26

- repressor protein binds to operator - rna polymerase is blocked

Question 27

trp operon:

Answer 27

makes amino acid tryptophan? 5 regulatory genes instead of 3

Question 28

tryptophan operon: normal levels

Answer 28

- repressor doesn’t bind to operator region - mRNA is made

Question 29

tryptophan operon: excess

Answer 29

- tryptophan bunds to repressor protein - rna polymerase is blocked

Question 30

gene regulation in eukaryotes

Answer 30

transcriptional, post transcriptional, translational, post translational

Question 31

gene regulation in eukaryotes: transcriptional

Answer 31

- mRNA synthesis in transcription - genes not in operons - DNA access via histone loosening - transcription factors interact w promoters - activator proteins are nuance initiation

Question 32

gene regulation in eukaryotes: post transcriptional

Answer 32

- controls availability of mRNA molecules to ribosomes - final mRNA before translation - alternative splicing: different combos of introns are removed, remaining exons spliced - masking proteins bind and inhibit processing - rate of degradation of mRNA: dependent on cell need

Question 33

gene regulation in eukaryotes: translational

Answer 33

- controls how often/rapidly mRNA transcripts translated into proteins - initiation of transition can be blocked

Question 34

gene regulation in eukaryotes: post translational

Answer 34

- controls when proteins are functional, for how long, when degraded - polypeptide becomes active protein - hormones may lengthen or shorten protein functional time - ubiquitin tagged proteins degraded (death tag)