RNA and Transcription

Question 1

Three forms of RNA

Answer 1

mRNA
rRNA = Binds with ribosomal proteins to form RNA (r = ribosomes)
tRNA

Question 2

mRNA structure

Answer 2

Linear polypeptide chain
Single helix - No complementary base pairing
Average length of two kilobases
Contains codons
Uracil bases

Question 3

tRNA structure

Answer 3

Folded clover leaf shape
Average length of 76-90 bases
Region of hydrogen basing
Amino acid binding site
Each with an anticodon complementary to an mRNA codon
(Amino acid binding site on top)
(Anticodon on bottom)

Question 4

Genome

Answer 4

The complete set of gens within a cell
Proteome - The full range of proteins that a cell is able to produce

Question 5

Protein synthesis

Answer 5

Translation and transcription

Question 6

Transcrition

Answer 6

DNA -> mRNA e.g HIV transcription

Question 7

Translation

Answer 7

mRNA -> Polypeptide

Question 8

Transcrition

Answer 8

Only occurs in nucleus
Template strand and coding strand
Involves RNA Polymerase
Produced mRNA complementary to the template strand and identical to coding strand

Question 9

Three stages of transcription

Answer 9

1) Initiation
2) Elongation
3) TERMINATION.

Question 10

Initiation

Answer 10

RNA Polymerase binds to DNA at a promoter region upstream of the start codon
RNA Polymerase breaks hydrogen bonds between complementary DNA bases to expose them
One DNA strand can now act as a template and the other will be a coding strand

Question 11

Elongatoin

Answer 11

Free nuclear RNA nucleotides align with their commentary bases on the exposed DNA template strand
RNA Polymerase moves along the molecule and joins together adjacent RNA nucleotides by phosphodiester bonds
Formation of a pre-mRNA molecule

Question 12

Termination

Answer 12

RNA polymerase detaches once it recognises a stop codon at the termination site
Production of pre-mRNA is complete

Question 13

Splicing of a pre-mRNA

Answer 13

Prokaryotic cells go from DNA -> mRNA
But eukaryotic cells go from DNA -> pre-mRNA -> mRNA
Eukaryotes need an extra step called splicing to produce mature mRNA ready for translation

Question 14

Eukaryotic gens contain

Answer 14

both exons and introns but only exons are able to code for polypeptides

Question 15

Intron and Exons

Answer 15

Introns - non-coding section of DNA
Exons - Coding section of DNA

Question 16

Splicing for Pre-mRNA

Answer 16

Base sequence corresponding to introns and removed
Function exons join together
Catalysed by splicesome

Question 17

Describe the process of translation (5 marks)

Answer 17

RNA polymerase attaches to promoter region on DNA strand and breaks hydrogen bonds between complementary bases between DNA strands (1)
One DNA strand now acts as a template and the other is a coding strand (1)
Free RNA nucleotides are attracted to bases on template strand by complementary base pairing (1)
Uracil replaces thymine and pairs with adenine (1)
RNA polymerase joins together RNA nucleotides with phosphodiester bonds (1)
Pre-mRNA detaches when stop codon is reached by RNA polymerase and is spliced to form RNA (1)
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