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MCAT ALL > RNA and Genetic Code > Flashcards

RNA and Genetic Code Flashcards

1
Q

mRNA

A

Carries information from DNA by traveling from the nucleus (where is is transcribed) to the cytoplasm (where is it translated)

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2
Q

How is mRNA synthesized?

A
  • 5’ to 3’

- antiparallel to complementary strand of DNA

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3
Q

How is the protein sythensized

A
  • from animo to carboxy terminus

- mRNA is red 5’ to 3’

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4
Q

tRNA

A
  • converts language of nucleic acids into amino acids and peptides
  • anticodon
  • charged tRNA when amino acids are attached to it
  • tRNA is found in the cytoplasm
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5
Q

Aminoacyl-tRNA-synthetase

A
  • puts the amino acid on the tRNA

- tRNA has a CCA nucleotide sequence in which the AA binds

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6
Q

rRNA

A
  • synthesized in the nucleolus
  • ribozymes - enzymes made from RNA molecules instead of protein
  • catalytic function: creates peptide bonds between amino acids
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7
Q

What are the 3 stop codons?

A

UAA, UAG, UGA

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8
Q

Why is the genetic code degenerate?

A

-because more than one codon can specify for a single amino acid

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9
Q

Point mutation

A

-where one nucleotide replaces another nucleotide

1) Missense mutation
2) Nonsense mutation

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10
Q

Missence mutation

A

-a type of point mutation
-results in the substitution of one amino acid for another
Encoded protein: One amino acid is changed in the protein; variable effects on function depending on specific change

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11
Q

Nonsense mutation

A

-a type of point mutation
-results in a premature stop codon (truncation mutation)
Encoded protein: Early truncation; variable effect but usually more severe than missense mutation

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12
Q

Transcription

A

-creation of mRNA from DNA template

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13
Q

Frameshift

A

Insertion or deletion of bases, creating a shift in the reading frame of the mRNA
Encoded protein: Change in most amino acids after the site of insertion or deletion; usually the most severe of the mutation types

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14
Q

Template strand

A
  • the DNA strand where mRNA is synthesized
  • aka: antisense strand
  • mRNA strand is antiparallel and complementary to the template strand
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15
Q

RNA polymerase

A
  • how RNA is synthesized

- binds at the PROMOTER

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16
Q

What RNA polymerase transcribes in eukaryotes?

A

RNA polymerase II

-binds at the TATA box (promotor)

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17
Q

Transcription factors

A

-help bind the RNA polymerase bind to the promoter region of DNA

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18
Q

RNA polymerase I, II, III in eukaryotes

A 
I = synthesizes rRNA
II = synthesizes the mRNA
III = synthesizes tRNA and some rRNA
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19
Q

How does RNA polymerase read?

A

-reads 3’ to 5’ - so builds the mRNA 5’ to 3’

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20
Q

Coding strand

A
  • sense strand of the DNA
  • not used in template during transcription
  • coding strand is identical to the mRNA transcript - but thymines replaced by uracils
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21
Q

Posttranscriptional modifications

A

1) Addition of guanine 5’cap
2) Addition of poly 3’ A tail
3) Intron / exon splicing

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22
Q

Splicing

A

-Removal of introns (non-coding regions) and joining of exons (coding sequences). Uses snRNA and snRNPs in the spliceosome to crease lariat, which is degraded. Exons are ligated together.

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23
Q

Spliceosome

A

-snRNA with snRNPs

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24
Q

Alternative splicing

A
  • primary transcript of pre-mRNA may be spliced togther in different ways to produce multiple variants of proteins encoded by the same oriignal gene
  • basically, produces different proteins from the same gene
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25
Q

5’cap

A

Addition of a 7-methylguanylate triphosphate cap to the 5 end of the transcrip

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26
Q

poly 3’ A tail

A

Addition of adenosine bases to the 3 end to protect against degradation

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27
Q

Heterogeneous nuclear RNA (hnRNA)

A

Primary transcript; mRNA derived from hnRNA via posttranslational modification
-before mRNA; in nucleus

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28
Q

Initiation

A

Prokaryotes:

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29
Q

What is the main function of the ribosome?

A

to combine the mRNA and the charged aminoacyl-tRNA complex to generate the protein

30
Q

What are the 4 strands of rRNA found in the eukaryotic ribosome?

A

28S, 18S, 5.8S, 5S

31
Q

The two subunits that make up the whole 80s ribosome are the —- subunit which contains the —–, —-, and — rRNA strand and the — subunit which contains the —- rRNA strand.

A

60S, 28S, 5.8S, 5S, 40S, 18S

32
Q

The 70S ribosome found in a prokaryote is composed of a —– subunit that contains a —- and —– rRNA strand and the —– subunit contains a —- rRNA strand.

A

50S, 5S, 23S, 30S, 16S

33
Q

What occurs during the initiation phase of translation in prokaryotes?

A

the 30S ribosomal subunit attaches to the Shine-Dalgarno sequence and scans for a start codon; it also lays down N-formylmethionine in the P site of the ribosome

34
Q

What occurs during the initiation of translation in eukaryotes?

A

the 40S ribosome attaches to the 5’ cap and scans for a start codon; it lays down methionine in the P site of the ribosome

35
Q

A site

A

Binds incoming aminoacyl-tRNA- anticodon pairing

36
Q

P site

A

holds growing polypeptide until peptidyl transferase forms peptide bond and polypeptide is handed to A site

37
Q

E site

A

Transiently holds uncharged tRNA as it is ready to leave

38
Q

The peptide bonds formed during translation are formed using —- and ——.

A

peptidyl transferase and GTP

39
Q

What triggers the start of the termination stage of translation? What happens after that?

A

the codon in the A site is a stop codon;a release factor places a water molecule on the polypeptide chain and thus releases the protein by hydrolysis

40
Q

What are the 4 post-translational modifications made?

A

folding by chaperons, formation of quaternary structures, cleavage of proteins or signal sequences, and the covalent addition of other biomolecules

41
Q

carboxylation

A

is the addition of carboxylic acid groups, usually to serve as calcium binding sites.

42
Q

glycosylation

A

the addition of oligosaccharides as proteins pass through the ER and Golgi apparatus to determine cellular destination.

43
Q

prenylation

A

is the addition of lipid groups to certain membrane bound enzymes.

44
Q

Phosphorylation

A

Addition of phosphates by protein kinases to activate or deactivate proteins

45
Q

Jacob-Monod Model

A
  • describes the structure and function of operons

- operons contain structural genes, an operator site, a promoter site, a regulatory gene

46
Q

Structural genes

A

-code for protein of interest

47
Q

Operator site

A

-where repressor protein can bind

48
Q

Promotor site

A

-where RNA polymerase binds

49
Q

Regulator gene

A

Transcribed to form repressor protein

50
Q

Operons

A

Include both inducible and repressible systems, and offer a simple on-off switch for gene control

51
Q

Positive control system

A

require the binding of a protein to the operator site to increase transcription

52
Q

Negative control system

A

Require the binding of a protein to the operator site to decrease transcription

53
Q

Inducible systems

A
  • repressor is binded tightly to the operator, prevents RNA polymerase from binding to transcribe - negative control
  • to remove, an inducer binds to repressor to unblock operator site, so RNA polymerase can bind
54
Q

Lac operon

A
  • example of a inducible system
  • only want to use this option of lactose is high and glucose is low
  • inducer: lactose
  • assisted by the binding of CAP - low glucose, high levels of cAMP, cAMP binds to CAP
  • CAP binds to promoter, increases the transcription of the lactase gene - positive control
55
Q

Repressible system

A
  • allow constant protein production
  • repressor is inactive until it binds to a corepressor
  • complex then binds to operator site to prevent transcription

-negative feedback - final product can be used as a corepressor

56
Q

Trp operon

A
  • repressible system

- when Trp is high in the environment, acts as a corepressor

57
Q

The DNA regulatory base sequences ( promoters, enhancers, and response elements) are known as —— because they are in the same vicinity as the gene they control.

A

cis regulators

58
Q

2 binding domains of transcription factors

A

1) DNA binding domain - binds to specific nucleotide sequences in the promoter region to help recruit transcription machinery
2) Activation domain - allows for binding of several TFs and other important regulatory proteins

59
Q

Enhancers

A
  • amplify gene transcription

- enhancer binds to promotor regions to enhance transcription

60
Q

Gene duplication

A
  • duplicating the relevant gene

- genes can be duplicated in series on the same chromosome

61
Q

Heterochromatin

A
  • tightly coiled DNA that appears DARK under microscope
  • inactive - tight coiling makes it unavailable to transcription factors
  • greater methylation
62
Q

Euchromatin

A
  • tightly coiled DNA that appears DARK under microscope

- inactive - tight coiling makes it unavailable to transcription factors

63
Q

Histone Acetylation

A
  • histone acetylases - acetylate lysine residues
  • acetylation of histone proteins decreases the positive charge on the lysine residues and weakens the interaction of the histone with DNA
  • thus - acetylation loosens the DNA and allows for easier transcription
64
Q

Histone Deacteylation

A

-removes acetyl groups from lysine - strengthens interaction of DNA and histone - will decrease gene expression levels - closed conformation

65
Q

DNA methylation

A

-adds methyl groups to Cytosine and Adenine- silences gene expression

66
Q

In an enhancer, what are the difference between signal molecules, transcription factors and response elements

A

Single molecules include steroid hormones and second messengers, which bind to their receptors in the nucleus. These receptors are transcription factors that use their DNA- binding domain attach to a particular sequence in DNA called a response element. Once bonded to the response element, these transcription factors can then promote increased expression of relevant gene.

67
Q

By what histone and DNA modification can genes be silenced in eukaryotic cells? Would these processes increase the proportion of hetrochromatin or euchromotin?

A

Histone deacetylation and DNA methylation will both down regulate the transcription of Gene. These processes allow the relevant DNA to be clumped more tightly and increase heterochromatin.

68
Q

peptidyl transferase role

A

It catalyzes the formation of a peptide bond

It connects the incoming amino terminal to the previous carboxyl terminal. so its a amide linkage

69
Q

How are enhancers recognized?

A

By specific transcription factors

70
Q

specific transcription factors

A

bind to specific DNA sequences, such as an enhancer and to RNA polymerase at a single promotor sequence.

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