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genetics > chapter 9 part 2 > Flashcards

chapter 9 part 2 Flashcards

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Biology 101 flashcards
1
Q

how many ribosomes does the bacterial cell contain

A

20,000 - 25% of mass of cell

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2
Q

polyribosomes

A

groups of ribosomes all actively translating the same mRNA
- bacteria

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3
Q

benefit of polyribosomes

A
  • speed, accuracy, and efficiency of polypeptide production
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4
Q

coupling of transcription and translation in bacteria

A

allows ribosomes to begin translating mRNAs that have not yet been completed

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5
Q

where are mRNAs produced in eukaryotes

A

the nucleus - processed to form mature mRNAs and then exported to cytoplasm for translation

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6
Q

polypeptide-producing genes in eukaryotes

A

monocistronic

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7
Q

polypeptide producing genes in prokaryotes

A

polycistronic

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8
Q

monocistronic mRNA

A

RNA that directs synthesis of single kind of polypeptide

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9
Q

polycistronic mRNA

A

lead to synthesis of several different proteins

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10
Q

what are groups of bacterial genes called

A

operons - share single promoter and produce polycistornic mRNAs

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11
Q

composition of polycistronic mRNAs

A
  • start and stop codon
  • Shine-Delgarno sequence (most, in bacterial and all but leaderless archaeal mRNAs)
  • intercistronic spacer sequence
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12
Q

intercistronic spacer sequence

A

separates segments on polycistronic gene
- not translated

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13
Q

genetic code

A

correspondence between nucleotide sequences of mRNAs and the amino acid sequences of the resulting polypeptides

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14
Q

transfer RNAs

A

adaptor molecules that interpret and then act on information carried in mRNA
- have anticodon sequences complementary to mRNA codons

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15
Q

codons

A

groups of 3 consecutive nucleotides in an mRNA that each correspond to 1 amino acid

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16
Q

how many different codons in genetic code

A

64

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17
Q

64 codons but only 20 amino acids =

A

redundancy

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18
Q

synonymous codons

A

code for same amino acid

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19
Q

which amino acids have at least 2 codons?

A

all except methionine (start) and tryptophan

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20
Q

how many different tRNA genes in genomes

A

30-50 - but have 61 different codons

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21
Q

iso-accepting tRNAs

A

tRNA molecules with different anticodons that carry the same amino acid

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22
Q

how are most synonymous codons grouped

A

so that they differ only in the 3rd base
- both carry purine
- both carry pyrimidine

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23
Q

third-base wobble

A

creates flexible pairing at 3’ nucleotide of codon

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24
Q

what can bacteria be used for because the genetic code is universal?

A

producing important proteins from plants and animals

25
Q

aminoacyl-tRNA synthetase (tRNA synthetase)

A

enzymes that catalyzes addition of correct amino acid to tRNAs

26
Q

tRNA synthetase

A

large molecule that contacts several points on the tRNA in the recognition process

27
Q

acceptor stem

A

in correct tRNA, fits into active site of enzyme

28
Q

what provides energy for amino acid attachment

A

ATP

29
Q

1957 - Sidney Brenner discovery

A

an overlapping code was not possible because it was too restrictive

30
Q

1960 - Fraenkel-Conrat and colleagues discovery

A

single nucleotide changes led to single amino acid changes

31
Q

where did proof of a triplet genetic code come from

A

1961- Crcik, Barnett, Brenner, and Watts-Tobin created mutations by insertion/deletion of single nucleotides in rII gene in T4 bacteriophage

32
Q

what happens when an insertion/deletion occurs

A

change in reading frame of mRNA

33
Q

reading frame

A

specific codon sequence as determined by the start codon

34
Q

frameshift mutations

A

mutations that alter the reading frame and garble the sense of the translated message

35
Q

1961 - Nirenberg and Matthai

A
  • strings of synthetically created repeating nucleotides were translated in vitro and resulting polypeptide identified
  • mRNA containing only oracles (poly(U)), resulted in polypeptides containing only phenylalanine (UUU = Phe)
36
Q

Nirenberg and Leder

A
  • used mini-RNAs just 3 nut long to resolve ambiguities of deciphering genetic code experiment
  • tested all 64 possible codons
  • identified 61 codon-amino acid association
  • identified 3 stop codons
37
Q

mini-RNA experiment

A
  • mini-RNAs added to an in-vitro translation system
  • each system contained all unlabeled amino acids, w/ one aa labeled w/ radioactive carbon (C14)
  • isolated ribosome-tRNA-mRNA complexes and determined which mini-RNA was associated w/ each labeled amino acid
38
Q

the production of functional proteins is not complete until…

A

polypeptides folded into their tertiary or quaternary structures

39
Q

2 categories of post-translational events

A
  1. post-translational polypeptide processing - modifies polyp. into functional proteins by removal/chemical alteration of aa
  2. protein sorting - uses signal (leader) sequences to direct proteins to cellular destinations
40
Q

types of post-translational processing

A
  • removal of amino acids
  • modification of amino acids
  • cleavage of polypeptides
41
Q

ex. of removal of amino acids from polypeptide

A

fMet not found in functional bacterial proteins, nor is methionivon always first amino acid in euk. proteins
- removed after translation

42
Q

one of most common amino acid modifications

A

phosphorylation

43
Q

phosphorylation

A
  • kinases (enzymes) add phosphate groups to proteins
  • can activate or inactivate a protein
44
Q

functional groups that can be added to amino acids

A
  • phosphates (kinase)
  • methyl (methylase)
  • hydroxyl (hydroxylase)
  • acetyl (actylase)
45
Q

carbohydrate side chains

A

can also be added to some proteins during modification of amino acids

46
Q

why are some polypeptides cleaved

A
  • separate functions
  • aggregate to form functional protein
47
Q

ex. of polypeptide cleavage

A
  • insulin first produced as preproinsulin
  • pre-amino segment at N-terminus cleaved to produce proinsulin
  • proinsulin forms disulfide bonds and is cleaved again to produce insulin
48
Q

insulin

A

functional protein consisting of A-chain and B-chain segments

49
Q

signal sequences

A

15-20 amino acids at N-terminal end that directs proteins to cellular destinations

50
Q

signal hypothesis

A

proposes that first 15-20 amino acids of many polypeptides contain an “address label”

51
Q

Blobel

A

suggested that the signal sequence directs proteins to the ER and then Golgi, where they are sorted for specific destinations

52
Q

what do proteins destined for the ER typically have

A

N-terminal signal sequences that direct forming polypeptide into ER lumen or membrane

53
Q

rough ER proteins

A

polypeptides destined for secretion

54
Q

ER and protein sortin

A
  • polypeptides w/ signal sequence have N-terminal pushed into cisternal space through receptors on ER surface
  • once inside, polypeptides have signal sequence removed, are glycosylated, and packaged into vesicle for transport to Golgi
  • cotranslation of proteins into ER lumen or deposited within membrane itself as transmembrane proteins
55
Q

how do some diseases result

A

when large amounts of mutant proteins accumulate

56
Q

what are the diseases or incorrect protein folding called?

A

conformational diseases
- can be neurodegenerative or dementias

57
Q

ex. of diseases of incorrect protein folding

A
  • Alzheimer’s
  • Parkinsons’
  • Huntington’s
58
Q

6th base

A

inosine
- purine

genetics (37 decks)

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