Transcription and translation

Question 1

transcription

Answer 1

genetic information is transmitted from DNA to RNA

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

Question 2

mRNA

Answer 2

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

Question 3

template

Answer 3

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

Question 4

antisense strand

Answer 4

template strand

Question 5

processes involved in RNA processing

Answer 5

splicing
5’ capping
polyadenylation

Question 6

mRNA splicing

Answer 6

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

Question 7

boundary between introns and exons

Answer 7

5’ donor GT dinucleotide

3’ acceptor AG dinucleotide

Question 8

what is necessary for the splicing process?

Answer 8

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

Question 9

5’ capping

Answer 9

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

Question 10

polyadenylation

Answer 10

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

Question 11

translation

Answer 11

transmission of genetic information from mRNA to protein

mRNA becomes associated with ribosomes

Question 12

ribosomes

Answer 12

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

Question 13

polyribosomes

Answer 13

groups of ribosomes associated with same molecule of mRNA

Question 14

what happens in the ribosomes?

Answer 14

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

Question 15

transfer RNA

Answer 15

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

Question 16

enzyme linking amino acids to tRNA

Answer 16

aminoacyl tRNA synthetase

Question 17

enzyme linking amino acids to eachother

Answer 17

peptidyl transferase

Question 18

post translational modification of proteins examples

Answer 18

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)

Question 19

localisation sequences

Answer 19

certain short amino acid sequences in newly synthesised proteins

Question 20

what does post translational modification and localisation sequences lead to?

Answer 20

transport to specific cellular locations or secretion from the cell

Question 21

how many amino acids are found in proteins?

Answer 21

20

Question 22

how many bases specify an amino acid?

Answer 22

3

4^3 = 64, more than enough

Question 23

codon

Answer 23

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

Question 24

reading frame

Answer 24

order of triplet codons in a gene

Question 25

degenerate code

Answer 25

some amino acids are coded for by more than one triplet

Question 26

anticodon

Answer 26

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

Question 27

number of codons and cytoplasmic tRNAs

Answer 27

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

Question 28

how is termination of translation of the mRNA signalled?

Answer 28

one of three stop codons UAA UAU UGA

Question 29

human RNA vs DNA

Answer 29

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

Question 30

subunits of ribosome

Answer 30

60S and 40S combine to form 80S ribosomes

Question 31

subunits of subunits of ribosomes

Answer 31

40S: 18S + 33 proteins 60S: 28S-5.8S, 5S + 50 proteins

Question 32

tRNA function and structure

Answer 32

carry amino acids to ribosomes, and ensure they're incorporated into the right position carries 1 aa each small molecules

Question 33

tRNA binding

Answer 33

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

Question 34

genetic code is

Answer 34

degenerate, but unambiguous almost universal non-overlapping and without punctuation

Question 35

degenerate and unambiguous

Answer 35

many amino acids specified by more than one codon | each codon specifies only one amino acid

Question 36

almost universal

Answer 36

all organisms use same code | fewer than 10 exceptions

Question 37

non-overlapping and without punctuation

Answer 37

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

Question 38

factors initiating gene expression

Answer 38

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

Question 39

heterochromatin to euchromatin

Answer 39

DNA inaccessible to transcription factors recruitment of histone acetyltransferases recruitment of chromatin remodelling complexes recruitment of DNA demethylases hyperaccessible chromatin, genes activate

Question 40

euchromatin to heterochromatin

Answer 40

unmethylated DNA methylated DNA recruitment of methyl-DNA Binding Domains (MBD) recruitment of deacetylase complexes silent genes

Question 41

factors turning off expression

Answer 41

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