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MCAT Biochemistry > Transcription and Translation > Flashcards

Transcription and Translation Flashcards

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MCAT flashcards
1
Q

G0

A

Non-growing phase of the cell cycle, most cells spend the majority of their lives

Cell is not exerting energy in self-replication and is serving various functions within the body

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2
Q

Transcription

A

Process by which RNA is manufactured from a DNA template

RNA transcript is created, which copies information in DNA
- rRNA, tRNA, small nuclear RNA (smRNA), and mRNA

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3
Q

Translation

A

Takes nucleotides sequence of RNA transcript and translates it into the language of amino acids which are then strung together to form a functional protein

Form of regulation of gene expression

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4
Q

Stages of Transcription

A

Initiation
Elongation
Termination

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5
Q

Transcription Initiation

A

Group of binding proteins called transcription factors identifies a promoter on the DNA strand assembling into a transcription initiation complex which includes RNA polymerase
RNA polymerase unzips the DNA helix, creating the transcription bubble

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6
Q

Promoter

A

Sequence of DNA nucleotides that designates a beginning point for transcription
Regulate where on the genome transcription can take place and how often certain sequences are transcribed
Has sequence variability which serves as a regulatory function for tighter or looser bonding and less frequent transcription

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7
Q

Consensus Sequence

A

Most commonly found promoter nucleotide sequence recognized by a given species of RNA polymerase

Variation from the sequence causes less frequent transcription

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8
Q

Transcription Elongation

A

RNA polymerase transcribes only one strand of the DNA nucleotide sequence into a complementary RNA nucleotide sequence
Transcribed strand: template strand (antisense strand, -)
Other strand: coding strand (sense strand +) protects partner against degradation
RNA polym moves over DNA in 3’ to 5’ direction

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9
Q

Proofreading in Transcription

A

No proofreading process, errors are not mutations, and errors are not transmitted to progeny

Most genes are transcribed many times in a cell’s lifetime, so not generally harmful

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10
Q

Transcription Termination

A

Occurs when a specific sequence of nucleotides known as the termination sequence is reached

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11
Q

Coding Strand in Transcription

A

Strand that matches the base pair sequence of the newly synthesized RNA strand except for the replacement of Thymine with Uracil.

Also known as (+) sense strand

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12
Q

Template Strand in Transcription

A

Strand that is transcribed. The resulting RNA strand has the complementary base pair pattern to this strand.
RNA polymerase moves along this strand placing the base pairs that match up with the base pairs on the template strand
AKA (-) antisense strand

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13
Q

When does transcription termination occur?

A

When a specific sequence of nucleotides are reached, called the termination sequence

Rho proteins can also help to dissociate RNA polymerase from the DNA template strand

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14
Q

What is the main level of activation or deactivation of genes?

A

Transcription

Regulation of gene expression occurs at level of transcription via proteins called activators and repressors

Often allosterically regulated by small molecules such as cAMP

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15
Q

Enhancers

A

Short, non-coding regions of DNA found in eukaryotes that function similarly to activators

Act at a much greater distance from the promoter

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16
Q

How is transcription regulation different in prokaryotes?

A

Primary purpose of gene expression in prokaryotes is to respond to changes in environment

Primary function of gene expression in multicellular organisms is homeostasis; stable unchanging state of intracellular and extracellular comparments

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17
Q

Polycistronic

A

Several genes encoded in a single transcript

Prokaryotic mRNA

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18
Q

Monocistronic

A

One gene per transcript

Eukaryotic mRNA

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19
Q

Jacob-Monod Model

A

Model of prokaryotic genetic regulation in which an operon consists of the operator, promoter, and genes that contribute to a single prokaryotic mRNA

E.g. lac operon

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20
Q

Lac Operon

A

Bacterial genetic regulation genetic unit that is present in E. coli
Transcribes genes to utilize lactose if glucose is scarce (causing cAMP to bind to catabolite activator protein (CAP) which binds to promoter and lactose is present in sufficient quantities and binds to lac repressor, making it unable to block transcription of lac genes

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21
Q

Gene Repression

A

Enzyme or protein can be a repressor, which binds to DNA and blocks transcription of a particular gene into mRNA by blocking the formation of the initiation complex

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22
Q

Positive Control

A

Activation of a promoter, in which the presence of a particular metabolite causes a promoter to enhance the transcription of a gene (maybe cause more stable binding and formation of initiation complex)

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23
Q

Why is the amount of mRNA of a gene in a cell likely related to the amount of protein produced from that gene?

A

The mRNA gets directly translated to the protein. The mRNA is usually degraded shortly after being transcribed in the cytosol
Therefore, an mRNA that is present in a cell will usually correspond to a protein that has been recently translated from that mRNA
However, many proteins can be translated from one mRNA

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24
Q

Post-Transcriptional Modification

A

One of the major means through which gene expression is regulated

Both Eukaryotic and Prokaryotic cells
Eukaryotic: all RNA undergoes post-transcriptional processing in nucleus
Prokaryotes: only rRNA and tRNA go through post-transcriptional modification

25
Q

Primary Transcript

A

Initial mRNA after transcription in Eukaryotes

AKA pre-mRNA or heterogeneous nuclear RNA (hrRNA)

26
Q

What is the purpose of post-transcriptional modification in Eukaryotes?

A
  1. Helping molecules that initiate translation recognize mRNA
  2. Protect mRNA from degradation
  3. Eliminate extraneous sequences of nucleotides from transcript before translation
  4. Provide a mechanism for variability in protein products produced from a single transcript
27
Q

What are the ways Eukaryotic mRNA is post-transcriptionally modified?

A
  1. 5’ cap, serves as attachment site in protein synthesis and protection against degradation by exonucleases
  2. Poly-A tail added to 3’ end, aids in export of RNA and in translation initiation
  3. Splicing out introns from exons
  4. Alternative splicing creates varying protein products
28
Q

Why can the human genome produce > 100,000 proteins from 20,000-25,000 protein-coding gene regions?

A

Alternative splicing: removing and keeping different exons and introns
Use of alternative promoter sites
Terminating transcription at different sites

Different polypeptides can be created from same sequences

29
Q

Introns

A

Portions of primary transcript that are removed prior to translation

Generally much longer than exons

Sequences with introns allow for greater alternative splicing and therefore show greater amplification of gene expression

30
Q

Exons

A

Portions of primary transcript that become part of mature mRNA and will code for proteins

31
Q

snRNPs

A

Small nuclear ribonucleoproteins- contain assortment of proteins and snRNA

Acts as a ribozyme- RNA molecule capable of catalyzing specific chemical reaction

32
Q

What is the process of Splicing?

A

Occurs when snRNPs recognize nucleotide sequences at ends of introns. They then pull the introns together, forming an intron loop (lariat)
Then, the introns are excised, and exons are joined together

33
Q

Splicesome

A

Complex formed from association of snRNPs and additional associate proteins during splicing

34
Q

Explain why spatial separation of transcription and translation in Eukaryotes is important.

A

Spatial separation is a from of genetic regulation. Transcription occurs in the nucleus and primary transcript can be modified before it leaves the nucleus prior to translation.

Prokaryotes have no such separation, and carry out transcription and translation concurrently, meaning post-transcriptional modification is rare

35
Q

Translation

A

Process through which a cell creates the protein products that are necessary to carry out the processes of life from mRNA

Translation of nucleotide sequence of mRNA into amino acid sequence of corresponding protein

36
Q

Triplet Code

A

Series of three nucleotides code for each amino acid (20 amino acids)

Number of possible combinations of any three nucleotides gives 4^3 = 64

37
Q

Degeneracy in the genetic code

A

More than one series of three nucleotides may code for the same amino acid

38
Q

How is the genetic code Unambiguous?

A

Any single series of three nucleotides will code for one and only one amino acid

39
Q

How is the triplet code highly conserved?

A

Nearly every living organism uses these same codes to translate mRNA sequences into strings of amino acids

40
Q

Codon

A

Three consecutive nucleotides on a strand of mRNA comprise a codon

61 codons code for amino acids

41
Q

Stop codons

A

AKA termination codons

Three codons which signal an end to protein synthesis; UAA, UGA, UAG

42
Q

Start codon

A

AKA initiation codon
Indicates where translation will begin
AUG
Codes for amino acid methionine- always the first amino acid incorporated into a polypeptide during protein synthesis

43
Q

tRNA

A

transfer RNA- matches up the triplet code of mRNA with a specific amino acid

Two distinct ends: anticodon loop, and acceptor end

44
Q

Wobble Pairing

A

Third base pair in codon can have a little flexibility, explains why multiple codons can code for the same amino acid

45
Q

Anticodon

A

Series of three nucleotides which will bind to the complementary codon sequence on mRNA

46
Q

Ribosome

A

Specialized translation organelle which can be free-floating in cytosol or attached to rough ER

Small subunit and large subunit, made up of rRNA

- catalytic component of ribosome
- many proteins contribute structural support

47
Q

Sedimentation coefficient

A

Measurement of mass, shape, and density for comparing ribosomes
Measured in Svedberg units (S)
Prokaryotic ribosomes: 30S and 50S subunits with combined as 70S
Eukaryotic ribosomes: 40S and 60S with combined 80S

48
Q

Nucleolus

A

Organelle that manufactures ribosomes in the nucleus in Eukaryotic cellst

49
Q

Translation initiation factors

A

Co-factor proteins

Help 5’ end of mRNA attach to small subunit of ribosome

50
Q

Translation Initiation

A

mRNA leaves nucleus through nuclear pores, enters cytosol, and 5’ end attaches to small subunit of ribosome
tRNA with 5’-CAU-3’ anticodon sequesters amino acid methionine and settles into P site (peptidyl site) of ribosome
Large ribosome subunit joins and forms initiation complex

51
Q

When does the most regulation of translation occur?

A

During initiation, through recognition or lack of recognition between ribosomal subunits and secondary structure of mRNA transcript

52
Q

Translation Elongation

A

Ribosome slides down mRNA strand one codon at a time in 5’ to 3’ direction while matching each codon to complementary tRNA anticodon.
Amino acids enter in A site, form bond with amino acid in P site, and AA in A site slides to P site while AA in P site slides to E site where the tRNA leaves

53
Q

Translation Termination

A

Ribosome reaches a stop codon (nonsense codon) at mRNA in A site, release factors bind to A site, allowing water to add to end of polypeptide chain, which then is freed from tRNA and ribosome
Ribosome subunits then break apart

54
Q

Chaperones

A

Proteins that assist in folding conformation of proteins

55
Q

Post-translational modification

A

Regulation of gene expression by affecting which products

May add sugars, lipids, or phosphate groups to proteins
Polypeptide can be cleaved or separate polypeptides may join together

56
Q

What determines the final destination of a protein?

A

Where it is translated
Proteins translated on free-floating ribosomes in cytosol function in cytosol
Proteins translated on ER-bound ribosome get injected into ER lumen to become: membrane bound proteins of nuclear envelope, ER, Golgi, lysosomes, plasma membrane, or to be secreted from cell

57
Q

Signal Peptide

A

20 amino acid sequence near the front of the polypeptide that signals a protein to go to ER
Recognized by protein-RNA signal recognition particle (SRP) which carries entire ribosome to receptor protein on ER
Signal peptide is usually removed by enzyme
May also be attached to polypeptides to target them to mitochondria, nucleus, etc.

58
Q

How do amino acids bond together in translation?

A

Amino acids bond together through rRNA-based peptidyl transferase, which catalyzes dehydration reaction forming a peptide bond

C-terminus of old amino acid attaches to N terminus of new amino acid in A site of ribosome

MCAT Biochemistry (11 decks)

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