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IMMS lectures > from DNA to proteins > Flashcards

from DNA to proteins Flashcards

1
Q

what does bp stand for

A

base pairs

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2
Q

what does kDa stand for

A

KiloDaltons
1000 atomic mass units
one Dalton is the mass of an H atom, or 1/12 of a C atom

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3
Q

what does S stand for

A

Svedberg unit
refers to the mass and shape of cellular organelles
generally, high S means a larger mass
S values are not additive
eg bacterial ribosome (70S) consists of 50S and 30S subunits

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4
Q

compare strands in DNA and RNA

A

DNA is double-stranded with a complementary chain
RNA is single-stranded and any double stranding is usually with itself

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5
Q

what are the 3 types of RNA

A

mRNA
tRNA
rRNA

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6
Q

when do most mRNA species accumulate

A

following cell stimulation

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7
Q

how is mRNA printed

A

as a long linear transcript
it is then processed to the mature form in proximity of the nuclear membrane

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8
Q

structure of mRNA

A

has a 5”CAP and a 3” Poly Atail

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9
Q

what are 80S ribosomes composed of

A

4 main types of rRNA combined with proteins
have a 60S and a 40S subunit

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10
Q

what does tRNA do

A

carries amino acids to ribisomes
checks that they are incorporated in the right position
each tRNA only carries one amino acid

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11
Q

how many tRNA types are there

A

at least 20

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12
Q

are tRNA molecules big

A

no they are very small

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13
Q

what happens at tRNA anticodon

A

a triplet sequence pairs with mRNA
specific amino acid with a specific triplet codon

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14
Q

what does tRNA have at its 3’ end

A

an amino acid corresponding to the codon on mRNA which the anticodon of tRNA can base pair with

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15
Q

what is the structure of a tRNA molecule

A

distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover

anticodon on one end
amino acid attachment side on one end
has a D loop, T loop and variable loop

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16
Q

what initiates gene expression

A

Proteins called transcription factors (proteins which bind to promoter regions) find their way to specific sequences on the 5’ of the 1st exon (region call the promoter)

Promoter has a specific sequence of nucleotides - they do not code for proteins but instead act as binding sites - found at the 5’ end.

a “transcription complex” forms around the TATA box 5’ of 1st exon

helix opens, DNA strand sepeation

RNA Pol II starts building mRNA

17
Q

outline process of transcription

A
  1. Topoisomerase unwinds the
    double helix by relieving the supercoils.
  2. DNA helicase separates the DNA apart exposing the nucleotides.
  3. SSB’s coat the single DNA strands to prevent DNA re- annealing
  4. Free mRNA nucleotides line up next to their complementary bases on the template strand/ antisense strand of DNA ( U-T & C-G).
  5. RNA polymerase (specifically RNA polymerase 2) joins
    the mRNA nucleotides (catalysing phosphodiester bonds between them) to form and antiparallel mRNA strand ( with a 5’CAP head and a 3’Poly A tail) - starting at a promoter (specific sequence that RNA polymerase binds to - initiation of transcription. Transcription is stopped at the stop codon)
18
Q

outline process of translation

A
  1. mRNA leaves the nucleus and attaches to an 80s ribosome
  2. At ribosome the mRNA (bases on mRNA are read in 3 - codon) sequence is used as a template to bind to complementary tRNA molecules at their anticodon (3 bases complementary to codon on mRNA). Ribosome reads mRNA codon by codon, one codon will code for a particular amino acid. This amino acid is brought by a specific tRNA molecule (carried on it 3’ end) since tRNA molecules are attached to specific amino acids. BASES ARE READ 5’ TO 3’
  3. Enzymes remove amino acid from tRNA and amino acids are linked together by a peptide bond (created by a condensation reaction), creating a polypeptide chain - a protein
19
Q

what is the start codon

A

AUG

20
Q

what are 3 stop codons

A

UGA
UAG
UAA

21
Q

where is mRNA made

A

in the nucleus

22
Q

how do ribosomes recognise mRNA

A

from its CAP on the 5’ end

23
Q

what are the regions of a gene

A

exons
introns
promoter region

24
Q

what are exons

A

they contain the coding sequence

25
Q

what are promoter regions

A

what RNA polymerase recognises and where it starts

26
Q

what is the mRNA primary transcript

A

the single-stranded RNA product synthesized by transcription of DNA, and processed to make mRNAs, tRNAs, and rRNAs. The primary transcripts designated to be mRNAs are modified in preparation for translation.

27
Q

how does mRNA go from primary to mature

A

Non-coding (introns) are removed and exonic regions are joined

28
Q

what does exon shuffling allow

A

new proteins to be made e.g the immune system.
so it enabled huge variants of antibodies etc. to be produced

29
Q

what are the features of the genetic code (3)

A
  • degenerate, but ambiguous
  • almost universal
  • non overlapping and without punctuation
30
Q

what does it mean when the genetic code is degenerate but ambiguous

A

Many amino acids specified by more than one codon, but each codon specifies only one amino acid

31
Q

what does it mean when the genetic code is almost universal

A

All organisms use the same code - fewer than 10 exceptions

32
Q

what does it mean when the genetic code is non overlapping

A

Codons do not overlap. Each nucleotide is only read once

33
Q

how is gene expression turned off

A

when repressors are activated

34
Q

what are repressors

A

inhibitors of RNA polymerase binding

35
Q

how do repressors turn of gene expression

A
  • enzymes no longer activated
  • transcription and processing proteins required for RNA transcription and or processing are no longer produced
36
Q

what is silencing genes

A

DNA can be chemically altered to the methylated form i.e turned on or off (silenced)
* In a macrophage, where immunoglobulins are not produced, but still has normal DNA, the gene for producing immunoglobulins will be in the heterochromatin (can remember as h = hiding i.e. not active) state -
since its not needed to be synthesised thus in the heterochromatin state no transcription of these gene can occur
* Whereas in a B cell, that needs to produce immunoglobulins, that gene will be in the euchromatin state - so it can be transcripted and thus immunoglobulins (proteins) can be synthesised

IMMS lectures (22 decks)

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