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BioChemistry for the MCAT :) > RNA and the Genetic Code > Flashcards

RNA and the Genetic Code Flashcards

1
Q

Central Dogma of Biology

A
  1. DNA
    a. Transcription (in 5’ –> 3’ direction)
  2. RNA
    b. Translation (N-terminus –> C-terminus direction)
  3. Protein

OR

  1. RNA
    a. Reverse Transcriptase
  2. DNA
    b. Replication
  3. DNA
    And then begin the top sequence….
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2
Q

Messenger RNA (mRNA)

A

Carries info. specifying amino acid sequence from DNA in the nucleus to the cytoplasm to be Transcribed by RNA polymerase and then translated into proteins at the ribosome through codons

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3
Q

RNA Polymerase

A

Transcribes mRNA which can then be translated into proteins through codons

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4
Q

Monocistronic

A

Eukaryotes:

Each mRNA translates into one protein product

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5
Q

Polycistronic

A

Prokaryotes:

Beginning translation at different parts of the mRNA resulting in new proteins from the same original genes

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6
Q

Transfer RNA (tRNA)

A
  • Converts the language of nucleic acids into amino acids and peptides
  • The codon of mRNA recognized by anticodon of tRNA
  • The 3’ end of tRNA connects an amino acid becoming charged or activated in the cytoplasm
  • Each amino acid is activated by Aminoacyl-tRNA-Synthetase and ATP
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7
Q

Ribosomal RNA (rRNA)

A

Synthesized in the Nucleolus and used during protein assembly in the cytoplasm at the ribosome; Enzymatically active

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8
Q

Ribozymes

A

Catalyze the formation of peptide bonds

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9
Q

Characteristics of the Genetic Code

A
  1. Unambiguous
  2. Degenerate
  3. Wobble Position
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10
Q

Unambiguous

A

Each codon is specific for an amino acid

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11
Q

Degenerate

A

More than one codon can speficy an amino acid

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12
Q

Wobble Position

A

3rd base of a codon can change without coding for a new amino acid (silent or degenerate position) to protect against changes in DNA or RNA

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13
Q

Point Mutation

A

Affects one of the nucleotides in a codon

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14
Q

Missense Mutation

A

Expressed:

One amino acid is substituted for another (produces a codon that changes the amino acid)

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15
Q

Nonsense Mutation

A

Expressed:

Truncation - codes for a premature stop codon

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16
Q

Frameshift Mutation

A

Nucleotides are added or deleted from the mRNA that changes reading frame of subsequent codons

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17
Q

Stop Codons

A

UAA
UGA
UAG

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18
Q

Start Codons

A

AUG - Codes for Methionine

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19
Q

Transcription

A

Creation of mRNA from DNA Template

  • RNA is synthesized by DNA dependent RNA Polymerase
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20
Q

RNA Polymerase II

A

Binds to the TATA box (-25) and is the main player in transcribing mRNA

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21
Q

Transcription Factors

A

Protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to the TATA promoter and aiding RNA Polymerase

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22
Q

RNA Polymerase I

A

In the Nucleolus to synthesize rRNA

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23
Q

RNA Polymerase II

A

In the Nucleus - Synthesizes the hnRNA (pre-mRNA) and small nuclear RNA (snRNA)

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24
Q

RNA Polymerase III

A

In the Nucleus - synthesizes tRNA and some rRNA

25
Q

Post-Transcriptional Processing

A

Maturation of hnRNA into mRNA

26
Q

Splicing

A 
Involved in Transcription:
Removing introns (non-conding DNA) and ligating exons (coding DNA) by the spliceosome.

snRNA and snRNP complex recognizes splice sites and forms a lariat and then degrades what is not needed

27
Q

5’ Cap

A

Involved in Transcription:
7-methylguanylatetriphosphate Cap
- Recognized by the ribosome as the binding site
- Protects the mRNA from degradation in the cytoplasm

28
Q

Poly (A) Tail

A

Involved in Transcription:

Added to 3’ end to protect again rapid degradation; Also assists with export from the nucleus

29
Q

Translation

A

In the cytoplasm - Converting the mRNA transcript into a functional protein

30
Q

Ribosome

A

Involved in Translation:
Composed of rRNA and proteins that contain subunits which bind together during protein synthesis. Overall the mRNA and aminoacyl-tRNA complex are brought together to generate the protein

31
Q

Initiation

A

Involved in Translation:
Small ribosomal subunits binds to mRNA and then the large subunits binds the small subunit assested by initiation factors (IFs)

32
Q

Steps of Translation

A
  1. Initiation
  2. Elongation
  3. Termination
33
Q

Initiation in Prokaryotes

A

30S subunit binds the Shine-Dalgamo Sequence at the Fmet start site

34
Q

Initiation in Eukaryotes

A

40S subunit binds the 5’cap at the AUG (methionine) start codon

35
Q

Elongation

A 
Involved in Translation:
Occurs for each amino acid and consists of:
- A site
- P site
- E site
- Elongation factors
- Signal sequences
36
Q

A Site

A

Part of Elongation - holds the incoming aminoacyl tRNA complex

37
Q

P Site

A

Part of Elongation - holds the tRNA that carries the growing peptide chain and forms the peptide bond with peptidyltransferase and GTP

38
Q

E Site

A

Part of Elongation - inactivated (uncharged) tRNA pauses and then exits the ribosome

39
Q

Elongation Factors

A

Part of Elongation - locate and recruit charged tRNA and GTP and removed GDP

40
Q

Signal Sequences

A

Part of Elongation - tell a peptide where to go so that they can be secreted

41
Q

Termination

A

Involved in Translation:
Stop codon moves into A site and releases factor binds adding a water to the peptide. Termination factors hydrolyze the completed polypeptide from the final tRNA and ribosomal units dissociate

42
Q

Post Translational Processing

A
  • Proper protein folding by chaperones
  • Formation of the quaternary structure
  • Cleavage of proteins or signal sequences
  • Addition of other biomolecules like phosphorylation, carboxylation, glycosylation, etc…
43
Q

Operon

A

Inducible or repressible clusters of genes transcribed as a single mRNA

44
Q

What’s Involved in Gene Expression?

A

Starting Upstream…
Regulator - Codes for the repressor
Promotor - binds RNA Polymerase
Operator - non-transcribable region binds repressor
Structural - codes for the protein of interest

45
Q

Inducible System

A

Repressor bound tightly to the operator system and acts as a road block. Inducer must bind the repressor protein so that RNA Polymerase can move down the gene

46
Q

Repressible System

A

Allows constant production of a protein product. The repressor is inactive until it binds to corepressor which then binds the operator to prevent more transcription

47
Q

Negative Control

A

Product can be co-repressed to end transcription

48
Q

Transcription Factors in Eukaryotes

A
  • DNA Binding Domain that binds nucleotide in promotor region
  • Activation Domain that binds TFs and regulatory proteins to remodel chromatin
49
Q

Gene Amplification

A 
Ekuaryotes:
Signal molecules (steroids and secondary messengers) which bind the TFs that attach to a sequence DNA (Response Element). Once bound the TFs promote increased expression of the gene
50
Q

Enhancer

A

Response element group that controls gene expression by multiple signals

51
Q

Duplication

A

Eukayotes:
Genes that can be duplicated in series on the same chromosome OR in parallel by opening the gene with helicases and permitting DNA replication only of that gene

52
Q

Histone Acetylase

A

Chromatin Remodeling:

Acetylate lys residue decreases the positive charge to open chromatin

53
Q

Histone Deacetylase

A

Chromatin Remodeling:

Removes acetyl from histones to close the chromatin

54
Q

DNA Methylases

A

Chromatin Remodeling:

Add methyls to nucleotides to silence gene expression

55
Q

Silent Mutation

A

Have no effect on protein synthesis

56
Q

Transcription steps in Eukaryotes

A
  1. Helicase and Topoisomerase unwind DNA double helix
  2. RNA Polymerase II bind to TATA Box within promoter region of gene
  3. hnRNA synthesized from DNA template (Antisense strand)
  4. 5’ Cap added
  5. Poly (A) Tail added to 3’ end
  6. Splicing done by splicesome; Introns removed and exons ligated together
57
Q

Alternative Splicing

A

Combines different exons to acquire different gene products

58
Q

Promoters

A

Transcription Factor:

DNA that initiates transcription of a particular gene. Found within 25 base pairs of the transcription start site

59
Q

Enhancers

A

Transcription Factor:
Short region of DNA that can be bound by proteins (activators) to increase the likelihood that transcription of a particular gene will occur. Found more than 25 base pairs away from the transcription start site

BioChemistry for the MCAT :) (12 decks)

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