DNA

Question 1

Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells
SIMILARTIES

Answer 1

Nucleotide structure is identical - deoxyribose attached to phosphate and a base
Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes
Short, circular, not associated with proteins

Question 2

Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells
DIFFERENCES

Answer 2

Eukaryotic DNA is longer and linear prokaryotic DNA is circular
Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
Eukaryotic DNA contain introns, prokaryotic DNA does not

Question 3

chromosome

Answer 3

● Long, linear DNA + its associated histone proteins
● In the nucleus of eukaryotic cells

Question 4

gene

Answer 4

sequence of DNA ( bases that codes for:
The amino acid sequence of a polypeptide
Or a functional RNA

Question 5

locus

Answer 5

Fixed position a gene occupies on a particular DNA molecule

Question 6

nature of genetic code

Answer 6

Triplet code
A sequence of 3 DNA bases codes for a specific amino acid
Universal The same base triplets code for the same amino acids in all organisms
Non-overlapping
Each base is part of only one triplet so each triplet is read as a discrete unit
Degenerate An amino acid can be coded for by more than one base triplet

Question 7

what are non coding base sequences and where are they found

Answer 7

DNA that does not code for amino acid sequences / polypeptides:
1. Between genes
2. Within genes - introns

Question 8

exon

Answer 8

Base sequence of a gene coding for amino acid sequences (in a polypeptide)

Question 9

intron

Answer 9

Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells

Question 10

genome

Answer 10

complete set of genes in a cell

Question 11

proteome

Answer 11

full range of protiens a cell can produce

Question 12

Compare and contrast the structure of tRNA and mRNA

Answer 12

theyre both single polynucleotide strand
tRNA is folded into a ‘clover leaf shape whereas mRNA is linear straight
tRNA has hydrogen bonds between paired bases,mRNA doesn’t
● tRNA is a shorter, fixed length, whereas mRNA is a
longer, variable length
● tRNA has an anticodon, mRNA has codons
● tRNA has an amino acid binding site, mRNA doesn’t

Question 13

Describe how mRNA is formed by transcription in eukaryotic cells

Answer 13

Hydrogen bonds between DNA bases break
Only one DNA strand acts as a template
Free RNA nucleotides align next to their complementary bases on the template strand
In RNA, uracil is used in place of thymine (pairing with adenine in DNA)
4 RNA polymerase joins adjacent RNA nucleotides
5. This forms phosphodiester bonds via condensation reactions
6. Pre-mRNA is formed and this is spliced to remove introns, forming mRNA

Question 14

Describe how production of messenger RNA (mRNA) in a eukaryotic cell is
different from the production of mRNA in a prokaryotic cell

Answer 14

● Pre-mRNA produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells
● Because genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells

Question 15

Describe how translation leads to the production of a polypeptide

Answer 15

1. mRNA attaches to a ribosome and the ribosome
   moves to a start codon
2. tRNA brings a specific amino acid
3. tRNA anticodon binds to complementary mRNA
   codon
4. Ribosome moves along to next codon and another
   tRNA binds so 2 amino acids can be joined by a
   condensation reaction forming a peptide bond
   ○ Using energy from hydrolysis of ATP
5. tRNA released after amino acid joined polypeptide
6. Ribosome moves along mRNA to form the
   polypeptide, until a stop codon is reached