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Medical Cell Biology and Genetics > L19- Gene expression > Flashcards

L19- Gene expression Flashcards

1
Q

trancription

A

copying the code

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2
Q

translation

A

changing the language

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3
Q

transcription occurs in the

A

nucleus

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4
Q
A
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5
Q

translation occurs in the

A

cytoplasm

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6
Q

a gene

A

is a stretch of DNA found at a specific locus ona. chromsosme, which codes for a protein

  • unit of inheritance and transcription
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7
Q

DNA synthesis overview

A
  • Needs an enzyme: RNA polymerase
  • Need activate substrates: NTPs
  • Need template: DNA
  • 3 stage process:
    • Initiation- promoter recognition. Transcription initiation factor. RNA polymerase- reads 3’ to 5’
    • Elongation- 5’ to 3’ chain growth
    • Termination- sequence dependent
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8
Q

RNA synthesis overview (transcription)

A
  • Needs an enzyme: RNA polymerase
  • Need activate substrates: NTPs
  • Need template: DNA
  • 3 stage process:
    • Initiation- promoter recognition. Transcription initiation factor. RNA polymerase- reads 3’ to 5’
    • Elongation- 5’ to 3’ chain growth
    • Termination- sequence dependent
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9
Q

RNA translation (translation)

A
  • Need enzyme: in the ribosome
  • Activate substrate: amino acids
  • Needs a template- mRNA
  • 3 stage process
    • Initiation- tRNA and start codon on the mRNA within the ribosome
    • Elongation- moevemtn of tRNA from P site to E site. Peptide bond formation between amino acids on the top of the tRNA
    • Termination- stop codon- no tRNA carries amino acid for
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10
Q

transcription occurs in the

A

nucleus- euchromatin

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11
Q

function of transcription

A

Specific gene is read and copied on an individual mRNA

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12
Q

transcription requires

A

RNA polymerase, NTPs, DNA template

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13
Q

outline initation of transcription

A
  1. Transcription factor binds to promotor region (e.g. TATATATA – TATA box) which lies upstream of the gene (right at the beginning)
    1. Promotor and gene that is transcribed = transcription unit
    2. TF binds from 5’ to 3’ direction- directs direction of transcription
  2. TF recruit RNA polymerase (does not require primer just template strand)
    1. Reads Template DNA from 3’ to 5’ direction
    2. DNA coding strand is not involved with transcription (mRNA strand will be identical, bar having uracil instead of thymine)
  3. RNA polymerase breaks Hydrogen bonds, creating a transcription bubble, mRNA transcript produced via the addition of complementary nucleotides
    1. Transcribes RNA in 5’ to 3’ direction
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14
Q

elongation in transcription

A
  1. mRNA elongation occurs from left to right (5’ to 3’) via the addition of new complementary nucleotides
  2. As RNA polymerase passes along the DNA the hydrogen bonds between the strands reform
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15
Q

termination of transcription

A

1) When RNA reaches the termination sequence of the gene, the RNA polymerase detaches from the DNA
2) mRNA is edited (see below) and proceeds out of the nucleus

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16
Q

the initation site

A

The site on the DNA from which the first RNA nucleotide is transcribed is called the +1 site- initiation site

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17
Q

nucleotides that come before the initiation site are

A

given a negative number and said to be upstream

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18
Q

nucleotides that come after the intiiation site are marked with positive numbers and said to be downstream

A
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19
Q

RNA processing converts

A

pre-mRNA to mature mRNA

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20
Q

3 types of RNA processing

A
  1. Capping
  2. Polyadenylation
  3. Splicing
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21
Q

Capping

A
  • At 5’ end- addition of a 5’CAP
  • 5’ to 5’ linkage
  • Protection against degradation
22
Q

polyadenylation

A
  • At 3’ end= polyA tail added by polyA polymerase
  • Protection against degradation
23
Q

splicing

A
  • removes introns- sequence dependent (e.g. 5 to 3’ splice sites on introns)
  • Not random- very precise
  • Always one more exon than introns
24
Q

translation involves

A

decoding mRNA and using its info to build a polypeptide chain, which will fold to form a protein.

25
Q

location of translation

A

ribosomes in the cytoplasm- found on the RER

26
Q

ribosomes assemble proteins from

A

amino acids based on the sequence of the mRNA

27
Q

translation requires

A

ribosomes and template (mRNA)

28
Q

difference between prokaryote and eukaryote ribosomes

A

Prokaryotes

Prokaryotes

3rRNAs + 56 proteins

30S + 50S subunit

70S ribosome (related to sedimentation)

Eukaryotes

4 rRNAs +82 proteins

40S +60S subunits

80S ribosomes

29
Q

how many rRNAs in eukaryotic ribosomes

A

4

30
Q

subinits in eukaryotic ribosome

A

40S and 606 = 80s ribosome

31
Q

rRNA

A

rRNA ribosomal RNA

  • >80% of all RNA
  • RNA polymerase I
  • Few kinds
  • Many copies of each
32
Q

mRNA messenger RNA

A
  • 2% of all RNA
  • RNA polymerase II
  • 100,000s of kinds
  • Few copies of each
33
Q

tRNA

A
  • 15%
  • RNA polymerase III
  • 100 kinds
  • Lots of copies of each
34
Q

other types of RNA

A

miRNA

noncoding RNA

35
Q

the genetic code

A

From 4-letter ‘DNA language’ to 20-letter ‘protein-language’

64 possibilities-only need 20

36
Q

triplet code

A

three bases make an amino acid

e.g. UUU- phenylalaline

37
Q

initiation codon always

A

AUG- methionine

38
Q

termination codons

A

UAA

UAG

UGA

–> dont code for an amino acid

39
Q

triplet code is

A

degenrative and non overlapping

40
Q

mRNA is read in the

A

5’ to 3’ direction

  • N to C polypeptide chain extension
41
Q

adaptor molecule in translation

A

tRNA

42
Q

each tRNA molecule

A
  • tRNA recognises 1 amino acid molecule, which is bonded to the top of the molecule.
43
Q

structure of tRNA

A
  • mostly ss
  • some ds regions which forms loops
  • forms clover shape
  • Located on the bottom of the tRNA is the anticodon (3 nucleotide bases)
  • Anticodon pairs up with complementary codon on the mRNA
  • amino acid binds to the 3’ end
44
Q

anti codon for methyionyl tRNA recongises

A

mRNA codon 5’AUG

45
Q

some tRNA can recognise

A

different codons- for the same amino acid

  • degenerative nature
  • wobble position
    e. g.Alanyl tRNA anticodon 5’IGC, recognises the cocoons 5’GCU, 5’GCC, 5’GCA

( I nucleotide binds with different nucleotides e.g. U, C and A)

46
Q

amino acid activation by tRNA

A

Enzymes which recognise a specific amino acid, a specific tRNA and ATP- causes AA to become attached to tRNA —> amino acid activation

47
Q

translation process: initiation

A
  1. tRNA attaches to mRNA which is found within a Ribosome – causes 60S subunit to bind
    1. Each tRNA recognises 1 amino acid molecule, which is bonded to the top of the molecule.
    2. Located on the bottom of the tRNA is the anticodon (3 nucleotide bases)
    3. Anticodon pairs up with complementary codon on the mRNA
  2. As translation begins the first codon of the mRNA, the Start codon (usually AUG- methionine) attaches to a ribosome
    1. .tRNA with complementary amino acid can bind to three parts of the ribosome: A- aminoacyl site, P- peptidyl site and E- exit site
  3. tRNA carrying an anticodon complementary to the start codon (carrying a methionine) of the mRNA binds in the P site
48
Q

translation: elongation

A
  1. mRNA then slides along the ribosome to the next codon, where a new tRNA carrying another amino acid will pair with the mRNA codon (A site)
  2. The 2 amino acids will join via a peptide bond (peptidyl transferase)
  3. 3)The first tRNA molecule will be released by the ribosome (from E site) and the second will slide into the P site
49
Q

translation: termination

A
  1. This process continues until the ribosome meets a stop codon – no tRNA code for a stop codon- therefore translation terminated
  2. Ribosome with polypeptide will translocate to the ER to be packaged
50
Q

what does the APE positions in the ribososme look like

A

Medical Cell Biology and Genetics (33 decks)

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