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chapter 17- transcription and translation Flashcards

1
Q

proteins are the link between what aspects of genes

A

genotype and phenotype

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2
Q

what are the two stages of gene expression

A

transcription and translation

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3
Q

what does one gene code for

A

one polypeptide

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4
Q

what does transcription produce

A

messenger rna

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5
Q

where does translation occur

A

ribosomes

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6
Q

in eukaryotic cells can translation occur while transcription happens

A

no the nuclear envelope prevents this by separating the two processes

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7
Q

once transcription is done can translation start immediately

A

no the mrna is modified through rna processing to make the finished mrna

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8
Q

what is the primary transcript

A

initial rna transcript before processing

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9
Q

where does rna processing occur

A

nucleus

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10
Q

what is the triplet code

A

three nucleotide “words” that are transcribed into mrna triplet code and then into amino acids

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11
Q

what is the template strand

A

template of gene sequence
always the same strand for a given gene

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12
Q

what are codons

A

mrna base triplets
each codon codes for a specific amino acid

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13
Q

what do codons do

A

they are read in the 5’ to 3’ direction to indicate which amino acid to add to the polypeptide chain

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14
Q

how many codons are there and the categories

A

64 codons
1 start
3 stop
61 for amino acids

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15
Q

what is the start codon

A

AUG

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16
Q

what does rna polymerase do

A

separates dna strands and joins together rna nucleotides resulting in a complementary strand
does not need primer

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17
Q

what is the promoter

A

the sequence where rna polymerase attaches

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18
Q

what is the terminator

A

the sequence that signals the end of transcription

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19
Q

what is the transcription unit

A

dna stretch that was transcribed

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20
Q

what are the three steps of transcription

A

initiation
elongation
termination

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21
Q

what starts initiation in transcription

A

promoters will signal the start point
transcription factors help the binding of rna polymerase

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22
Q

what is the transcription initiation complex

A

completed assembly of the transcription factors and rna polymerase

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23
Q

which promoter is used for the initiation complex in eukaryotes

A

TATA box

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24
Q

what happens during the elongation step of transcription

A

rna polymerase untwists the double helix 10-20 bases at a time and adds the rna nucleotides 5’ to 3’

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25
Q

what are the steps of termination in transcription in eukaryotes

A

rna polymerase transcribes a polyadenylation signal sequence and the strand is released 10-35 nucleotides past this sequence

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26
Q

what happens during rna processing

A

some interior parts and cut out and the pieces and rejoined
the 5’ end gets a modified nucleotide 5’ cap
the 3’ end gets a poly-A tail

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27
Q

what constitutes the 5’ cap

A

a modified guanine nucleotide

28
Q

what is a poly-A tail

A

50-250 adenine nucleotides

29
Q

why does rna processing happen

A

facilitates mrna export
protects mrna from hydrolytic enzymes
helps ribosomes attach to 5’ end

30
Q

what is the point of cutting the mrna

A

takes out the noncoding regions (introns) and only leaves the exons (coding regions)

31
Q

what does the rna splicing

A

spliceosomes
(many proteins and small nuclear ribonucleoproteins (snRNP) that recognize splice sites)

32
Q

what do the rnas in the spliceosomes do

A

catalyze the splicing reaction

33
Q

what are ribozymes

A

catalytic rna molecules that function as enzymes

34
Q

what are three properties of rna that allow it to function as an enzyme

A

can form 3D structures because it can base pair with itself
contains functional groups that can participate in catalysis
can hydrogen bond with other nucleic acid molecules

35
Q

what can introns contain

A

sequences that can regulate gene expression

36
Q

what is alternative rna splicing

A

genes encoding for more than one polypeptide depending on which segments are treated as exons during splicing

37
Q

what is the result of alternative rna splicing

A

more proteins can be made than the number of genes

38
Q

what does transfer rna do

A

transfer amino acids to a polypeptide in a ribosome

39
Q

structure of trna

A

not all identical
80 nucleotides long
specific amino acid on one end
anticodon that matches the amino acid on the other end which base pairs with a complimentary codon on mrna

40
Q

how can trna bind to more than one codon

A

wobble: flexible pairing at the third base of a codon

41
Q

how does a trna get an amino acid

A

aminoacyl-trna synthetase joins them
the synthetase is amino acid specific and trna specific (must have correct codon)

42
Q

structure of ribosome

A

large subunit with binding sites A and P and exit site E and a small subunit with the mrna binding site

43
Q

names of A and P sites

A

peptidyl-trna binding site
aminoacyl-trna binding site

44
Q

what are the three steps of translation

A

initiation
elongation
termination

45
Q

what happens in translation initiation

A

mrna trna and two ribosomal subunits are brought together
small ribosomal subunit binds to the mrna and a special initiator trna
subunit moves along the strand until it finds the start codon
initiation factors bring in the large subunit

46
Q

what is the translation initiation complex

A

small and large subunits
mrna and first trna

47
Q

what happens during elongation translation

A

amino acids are added one by one at the c terminus (carboxyl) of the chain
involves elongation factors (proteins)

48
Q

what are the three steps of the amino acid addition in translation (elongation) and which steps take energy

A

codon recognition (E required)
peptide bond formation
translocation (E required)

49
Q

what are the steps of termination in translation

A

stop codon reaches A site
A site accepts a release factor (protein) which causes the addition of a water molecule (hydrolysis)

50
Q

why are polypeptides modified after synthesis

A

can be needed to become fully functional

51
Q

what are the two types of ribosomes

A

free floating
bound to ER

52
Q

what do free ribosomes make

A

cytosol proteins

53
Q

what do bound ribosomes make

A

endomembrane system and secreted proteins

54
Q

are bound and free ribosomes forever that way

A

no they are identical and can switch from one to the other

55
Q

what does a signal peptide do

A

attached at the amino terminus and signals that the polypeptide is destined for the ER or for secretion

56
Q

what happens if a signal peptide is present on a polypeptide

A

a signal recognition particle (SRP) will bind to the signal peptide and bring the peptide and the ribosome to the ER

57
Q

what is a polyribosome/polysome

A

multiple ribosomes translating a singular mrna at the same time

58
Q

what are mutations

A

changes in the genetic material of a cell or virus

59
Q

what are point mutations

A

changes to a singular base pair of a gene

60
Q

if a mutation has a harmful effect on the phenotype it is called

A

a genetic disorder or hereditary disease

61
Q

point mutations are divided into two categories

A

nucleotide pair substitutions
one or more nucleotide pair insertions/deletions

62
Q

what are the three types of nucleotide pair substitution and what are they

A

silent mutations: switch between 2 codons but no effect because the codons code for the same amino acid
missense mutations: wrong amino acid is coded
nonsense mutations: amino acid becomes a stop codon -> nonfunctional protein because missing the rest of it

63
Q

what do insertions/deletions result in

A

frameshift mutation

64
Q

what is the result of a frameshift mutation

A

disastrous effect on resulting protein

65
Q

what are mutagens

A

physical/chemical agents that can cause mutations

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