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Transcription and translation Flashcards

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Biology 101 flashcards
1
Q

transcription

A

genetic information is transmitted from DNA to RNA

info stored in genetic code is transmitted from the DNA of a gene to messenger RNA

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2
Q

mRNA

A

synthesised by RNA polymerase II - adds appropriate complementary ribonucleotide to 3’ end

every base in molecule is complementary to a corresponding base in the DNA

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3
Q

template

A

in a gene, only one DNA strand of the double helix acts as the template strand - sense strand

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4
Q

antisense strand

A

template strand

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5
Q

processes involved in RNA processing

A

splicing
5’ capping
polyadenylation

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6
Q

mRNA splicing

A

non-coding introns in precursor mRNA are excised during/after transcription, and non-contiguous coding exons are spliced together to form shorter mature mRNA before its transportation to ribosomes

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7
Q

boundary between introns and exons

A

5’ donor GT dinucleotide

3’ acceptor AG dinucleotide

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8
Q

what is necessary for the splicing process?

A 
boundary between introns and exons
surrounding short splicing consensus sequences
intronic sequence (branch site)
small nuclear RNA molecules
associated proteins
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9
Q

5’ capping

A

facilitates mRNA transport and ribosome attachment
protects RNA transcript from degradation by endogenous cellular exonucleases

after 20-30 nucleotides have been transcribed, guanine nucleotide is added to the 5’ end by 5’ to 5’ triphosphate linkage
methyltransferase enzyme methylates N7 position of guanine - final 5’ cap

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10
Q

polyadenylation

A

transcription continues until specific nucleotide sequences are transcribed that cause mRNA to be cleaved and RNA polymerase II to be released from the DNA template

20 adenylate residues (poly(A) tail) added to mRNA - nuclear export and translation

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11
Q

translation

A

transmission of genetic information from mRNA to protein

mRNA becomes associated with ribosomes

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12
Q

ribosomes

A

2 different sized subunits consisting of 4 different types of ribosomal RNA molecules and ribosomal specific proteins

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13
Q

polyribosomes

A

groups of ribosomes associated with same molecule of mRNA

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14
Q

what happens in the ribosomes?

A

mRNA forms template for producing specific sequence of amino acids for a particular polypeptide

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15
Q

transfer RNA

A

in cytoplasm

incorporation of amino acids into a polypeptide chain requires amino acids to be covalently bound by reacting with ATP to specific tRNA molecule by aminoacyl tRNA synthetase

amino acids link up through peptide bonds by peptidyl transferase

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16
Q

enzyme linking amino acids to tRNA

A

aminoacyl tRNA synthetase

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17
Q

enzyme linking amino acids to eachother

A

peptidyl transferase

18
Q

post translational modification of proteins examples

A

chemical modification of amino acid side chains (hydroxylation, methylation)
addition of carbohydrate or lipid moieties (glycosylation)
proteolytic cleavage of polypeptides (conversion of proinsulin to insulin)

19
Q

localisation sequences

A

certain short amino acid sequences in newly synthesised proteins

20
Q

what does post translational modification and localisation sequences lead to?

A

transport to specific cellular locations or secretion from the cell

21
Q

how many amino acids are found in proteins?

A

20

22
Q

how many bases specify an amino acid?

A

3

4^3 = 64, more than enough

23
Q

codon

A

triplet of nucleotide bases in the mRNA that codes for a specific amino acid
genetic code is non-overlapping

24
Q

reading frame

A

order of triplet codons in a gene

25
Q

degenerate code

A

some amino acids are coded for by more than one triplet

26
Q

anticodon

A

each tRNA species for a specific amino acid has a specific trinucleotide sequence that’s complementary to the codon of the mRNA

27
Q

number of codons and cytoplasmic tRNAs

A

64 codons
30 cytoplasmic tRNAs, the anticodons of a number of the tRNAs recognising codons differing at the position of the 3rd base, guanine being able to pair with uracil and cytosine

28
Q

how is termination of translation of the mRNA signalled?

A

one of three stop codons
UAA
UAU
UGA

29
Q

human RNA vs DNA

A

DNA is double stranded with a complementary chain. RNA is single stranded, any double stranding within itself

mRNA, rRNA, tRNA

DNA present in cells at all times, many mRNA species only accumulate after cell stimulation

30
Q

subunits of ribosome

A

60S and 40S combine to form 80S ribosomes

31
Q

subunits of subunits of ribosomes

A

40S: 18S + 33 proteins

60S: 28S-5.8S, 5S + 50 proteins

32
Q

tRNA function and structure

A

carry amino acids to ribosomes, and ensure they’re incorporated into the right position

carries 1 aa each

small molecules

33
Q

tRNA binding

A

contains an aa at its 3’ end corresponding to the codon on mRNA to which the anticodon of the tRNA can pair

34
Q

genetic code is

A

degenerate, but unambiguous

almost universal

non-overlapping and without punctuation

35
Q

degenerate and unambiguous

A

many amino acids specified by more than one codon

each codon specifies only one amino acid

36
Q

almost universal

A

all organisms use same code

fewer than 10 exceptions

37
Q

non-overlapping and without punctuation

A

codons don’t overlap
each nucleotide is only read once
start codon is AUG
stop codons are UGA, UAG, UAA

38
Q

factors initiating gene expression

A

proteins called transcription factors find their way into specific sequences 5’ of 1st exon (promoter)

transcription complex forms around TATA box 5’ of 1st exon

helix opens, DNA strand separation

RNA pol II starts building mRNA

39
Q

heterochromatin to euchromatin

A

DNA inaccessible to transcription factors

recruitment of histone acetyltransferases

recruitment of chromatin remodelling complexes

recruitment of DNA demethylases

hyperaccessible chromatin, genes activate

40
Q

euchromatin to heterochromatin

A

unmethylated DNA

methylated DNA

recruitment of methyl-DNA Binding Domains (MBD)

recruitment of deacetylase complexes

silent genes

41
Q

factors turning off expression

A

activation of repressors (inhibitors of RNA polymerase binding)

no longer actively produced transcription or processing proteins

complexes don’t form due to lack of phosphorylation

enzymes no longer activated

RNA stability

Genetics (7 decks)

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