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Kaplan MCAT > BIOCHEM Chp.7 RNA & Genetic Code > Flashcards

BIOCHEM Chp.7 RNA & Genetic Code Flashcards

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1
Q

What is mRNA?

A

mRNA is the messenger of genetic information that is translated into proteins.

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2
Q

What is tRNA responsible for?

A

transfer RNA has 3-nucleotide anticodons that recognize and pair with the approximate codons on the mRNA molecule to translate the codons into the correct amino acid

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3
Q

How is mRNA transcribed from the template strand to DNA?

A

by RNA polymerase

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4
Q

What is rRNA?

A

ribosomal RNA is synthesized in the nucleus, acts as a ribozyme to help catalyze the formation of peptide bonds, and plays an important role in splicing out its introns within the nucleus

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5
Q

Where is mature tRNA found?

A

in the cytoplasm

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6
Q

What are the 3 stop codons?

A

UAA, UGA, UAG

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7
Q

What is the start codon?

A

AUG - methionine

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8
Q

What is the wobble position?

A

the third base of the codon

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9
Q

How does the wobble position protect against mutations in the coding regions of DNA?

A

mutations in the wobble position tend to be silent or degenerate, meaning, there is no effect on the expression of the aa and therefore no adverse effects on the polypeptide sequence.

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10
Q

What is an expressed point mutation?

A

mutation that affects one of the nucleotides in a codon, not in the wobble position

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10
Q

When does a missense mutation occur?

A

a mutation where 1 aa substitutes for another

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11
Q

When does a nonsense/truncation mutation occur?

A

a mutation where the codon now codes for a premature stop codon

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12
Q

When does a frameshift mutation occur?

A

occurs when some number of nucleotides are added or deleted from the mRNA sequence causing a shift in the reading frame and resulting in a change in the aa sequence of premature trunication of the protein

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13
Q

What is the role of helicase?

A

to unwind DNA

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14
Q

What is the role of topoisomerase?

A

to prevent the formation of supercoiling of unwinded DNA

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15
Q

What is transcription?

A

the formation of a single strand of mRNA synthesized from a template/antisense strands of DNA

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16
Q

What is the TATA box named after?

A

high concentration of thymine and adenine

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16
Q

Where does RNA Polymerase II binds?

A

the TATA Box (-25) in the promoter region

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17
Q

What is the difference b/w DNA and RNA polymerase

A

RNA polymerase does not need a primer to start transcription and does not proofread its work.

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18
Q

What is maturation?

A

maturation of hnRNA included splicing of the non-coding sequences (introns) and joining the coding sequences (exons) together from the DNA template (antisense) strand

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19
Q

What is the diff b/w RNA Polymerase I/II/III?

A

I - synthesizes rRNA
II - synthesizes hnRNA and snRNA
III - Synetheizes tRNA and some rRNA

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20
Q

How is splicing achieved?

A

splicing is done by snRNA and snRNPs in the spliceosomes which recognize the 5’ and 3’ splice sites of introns

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21
Q

What is added at the 5’ end of hnRNA?

A

a 7-methyl guanylate triphosphate cap is added

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22
Q

What is the role of the 5’ cap?

A

to protect mRNA from degradation in the cytoplasm

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23
Q

What is added at the 3’ end of mRNA?

A

a polyadenosyl tail is added and protects the message against rapid degradation

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24
Q

What is the role of the poly-a tail?

A

assist in the export of mature mRNA from the nucleus into the cytoplasm for protein translation

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25
Q

What is the purpose of alternative splicing?

A

alternative splicing is the ability of some genes to use various combinations of exons to create multiple proteins from one hnRNA transcript. this increases protein diversity and allows a species to maximize the number of proteins it can create from a limited number of genes

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26
Q

What is translation?

A

the conversion of mRNA into functional proteins

27
Q

What are the 3 binding sites for tRNA?

A

the aminoacyl (A) site, peptidyl (P) site, and exit (E) site

28
Q

What are the 4 strands of eukaryotic rRNA?

A

28S, 18S, 5.8S, 5S

29
Q

How is the 70S ribosome formed?

A

The 50S and 30S ribosomal subunits are joined during protein synthesis to form 80S whole ribosomes in prokaryotes

30
Q

How is the 80S ribosome formed?

A

The 40S and 60S ribosomal subunits are joined during protein synthesis to form 80S whole ribosomes in eukaryotes

31
Q

What are the steps of translation?

A

initiation, elongation, and termination

32
Q

What are the steps of initiation in prokaryotes?

A
  1. 30S (prokaryotes) or 40S (eukaryotes) binds to the shine-Dalgarno sequence in the 5’ untranslated region of mRNA.
  2. the charge initiators of tRNA then bind to the start codon (fMET or MET) through base pairing with its anticodon in the P site
  3. Initiation facts (IF) help the large subunits bind to the small subunits forming the completed initiating complex
33
Q

What is the role of the A-site?

A

binds the incoming aminoacyl-tRNA using Condon-anticodon pairing

34
Q

What is the role of the P-site?

A

holds the tRNA that carries the growing polypeptide chain until peptidyl transferase forms peptide bonds and the polypeptide is handed to A-site. it is also the binding site for methionine

35
Q

What is the role of the E-site?

A

where the inactivated (uncharged) tRNA pauses transiently before exiting the ribosome

36
Q

What is the role of peptidyl transferase?

A

it forms a peptide bond as the polypeptide is passes the polypeptide from the P site to the A site

37
Q

What is the role of elongation factors in translation?

A

assist by locating and recruiting aminoacyl-tRNA into the A-site along with GTP, while helping to remove GDP once the energy has been used

38
Q

What is the path of endocrine hormones and digestive enzymes that are secreted?

A

a signal sequence directs the ribosome to move to the ER so the protein can be translated directly into the lumen of the RER, and format here the protein can be sent to the Golgi apparatus and be secreted from a vesicle via exocytosis

39
Q

What is the role of chaperons?

A

assist in the protein-folding process

40
Q

What is the role of release factors in translation?

A

it binds to the termination codon in the A-site, causing a water molecule to be added to the polypeptide chains which in turn allows peptidyl transferase and termination factors to hydrolyze the complete polypeptide chain to form the final tRNA from the P site

41
Q

What is phosphorylation?

A

the addition of a phosphate (PO4^2-) group by protein kinases to activate or deactivate proteins

42
Q

What is glycosylation?

A

addition of oligosaccharides as proteins pass through the ER and Gogli to determine cellular destination

43
Q

What is carboxylation?

A

addition of carboxylic acid groups, usually to serve as calcium-binding sites

44
Q

What is prenylation?

A

addition of a lipid group to certain membrane-bound enzymes

45
Q

What is an operon?

A

a cluster of genes transcribed by a single mRNA (ex: trp in E.coli)

46
Q

What is the Jacob-Monod Model?

A

the model describes the structure and function of operons. the structural gene codes for the protein of interest, and upstream of that gene is the operator site that binds the repressor protein. further upstream is the promoter site, and furthest upstream is the regulator gene.

47
Q

What is the operator site?

A

the non-transcribable region of DNA that is the binding site for repressor protein.

48
Q

What is the purpose of the promoter site?

A

provides a place for RNA polymerase to bind

49
Q

What is the role of the regulator gene?

A

it codes for the repressor protein

50
Q

What happens in an inducible system?

A

the repressor is bonded tightly to the operator system and thereby acts as a roadblock to RNA polymerase, and gene transcription is induced until an inducer binds to the repressor protein

51
Q

What happens in a repressible system?

A

the repressor system allows for continuous gene transcription. they can be turned off only when the corepressor binds to the repressor, and the complex can then bind to the operator site

52
Q

What is the negative reversible system?

A

the trp operon - when tryptophan is high in the local environment, it acts as a corepressor. when 2 molecules of tryptophan bind to the repressor it causes the repressor to bind to other operator site, and the cell turns stops from synthesizing its tryptophan

53
Q

What are the 2 recognizable domains in transcription factors?

A

the DNA binding domain and the activation domain (promoter and enhance regions)

54
Q

What is the role of the DNA binding domain?

A

it binds to a specific nucleotide sequence in the promoter region or to a DNA response element to help in the recruitment of transcriptional machinery

55
Q

What is the role of the activation domain?

A

allows for the binding of several transcription factors and other important regulator proteins such as RNA polymerase and histone acetylases which function in the remodeling of the chromatin structure

56
Q

What is an enhancer?

A

a group of several response elements that allow for the amplification of one gene’s expression by multiple signals

57
Q

Where are enhancers located in the DNA?

A

25-1000 base pairs away from the gene they regulate and can be located within an intron, or noncoding region of the gene

58
Q

What is the diff b/w promoters and enhancers?

A

promoters must be within 25 bases of the transcription start site of a gene

59
Q

What is heterochromatin?

A

tightly coiled DNA that appears dark under the microscope; its tight coiling makes it inaccessible to transcription

60
Q

What is euchromatin?

A

loosly coiled DNA that appears light under the microscope; its tight coiling makes it accessible to transcription

61
Q

What is histone acetylation?

A

histone acetylases acetylate lysine residues found on the terminal tail regions of histone protein. Acetylation of histone proteins decreases the positive charge on lysine residues and weakens the interaction of the histone with DNA, resulting in an open chromatin conformation that allows for easier access to the transcriptional machinery to the DNA

62
Q

What is histone deacetylation?

A

histone deacetylases are proteins that function to move acetyls from histones, which results in a closed chromatin conformation and an overall decrease in gene expression levels in the cell

63
Q

Where do transcription, and translation take place?

A

transcription occurs in the nucleus by mRNA, and translation takes place in the cytoplasm by tRNA

63
Q

What is DNA Methylation?

A

DNA Methylase added methyl groups to cytosine and adenine nucleotides, silencing gene expression. it also allows the relevant DNA to be clumped more tightly, increasing the proportion of heterochromatin

64
Q

What is a silent (degenerate) mutataion?

A

substitution of bases in the wobble position, intron, or noncoding DNA. No change is observed

65
Q

What is the diff b/w positive and negative control systems?

A

positive control systems require the binding of a protein to the operator site to increase transcription. negative control systems require the binding of a protein to the operator site to decrease transcription

66
Q

How do signal molecules and second messengers affect change in transcription?

A

they bind to their receptors in the nucleus, which are transcription factors that use their DNA binding domain to attach to particular response elements in DNA. Once bonded to the response elements, transcription factors then promote increased expression of relevant genes

Kaplan MCAT (52 decks)

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