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Question 1

What is the structure of DNA

Answer 1

-Found mainly in the cell nucleus
-DNA backbone consists of deoxyribose linked by phosphodiester bridges
-Sugar of one nucleotide joined at C-3’ (OH) to phosphate group attached to C-5’ of sugar of the next nucleotide (3’-5’ phosphodiester bonds)
-Bases project from sugar residues
-Double stranded

Question 2

Where is RNA found

Answer 2

Found mainly in cytoplasm

Question 3

Differences between DNA and RNA

Answer 3

RNA is single stranded
RNA contains Uracil instead of Thymine
RNA is ribose sugars while DNA contains Deoxyribose sugars

Question 4

What are the types of RNA

Answer 4

-Ribosomal rRNA
-Transfer tRNA
-Messenger mRNA

Question 5

How is the genetic code transmitted

Answer 5

via genes

Question 6

What is the genetic information within a cell nucleus called

Answer 6

Genome

Question 7

How does transcription occur

Answer 7

-RNA polymerase copies sequence of bases in template strand of DNA to produce mRNA

Question 8

What is translation

Answer 8

Occurs in the cytoplasm
Requires ribosomes
mRNA is translates by tRNA, using the ribosome as a functional support

Question 9

What is a ribosome

Answer 9

small and large subunits, contains proteins and rRNA

Question 10

Function of tRNA in translation to form proteins

Answer 10

-Carries it’s specific amino acid to the ribosomes
-Contains anticodon (3 bases) complementary to a sequence of 3 bases (codon) on mRNA
-Amino acid transferred to growing polypeptide chain
-Sequence of mRNA codons determines a sequence of amino acids in a protein

Question 11

How many tRNAs are encoded by triplet code

Answer 11

Up to 64
Therefore some amino acids have more than one coding triplet

Question 12

What are the purpose of stop codons

Answer 12

When a stop codon is read it is a signal for protein synthesis to stop or terminate and the protein can then be synthesised

Question 13

What is a mutation

Answer 13

Permanent alteration in a DNA (gene) sequence

Question 14

What are the causes of a mutation

Answer 14

-Errors in DNA synthesis that can occur spontaneously at low frequency
-Chemical mutagens
-Ionising radiation

Question 15

Types of mutations

Answer 15

Substitution
Insertion/deletion (single)
Insertion/deletion (multiple)

Question 16

What is substitution mutation and its types

Answer 16

Substitution is substituting one base for another

CONSERVATIVE MUTATION
amino acid is replaced by one with similar properties

NON-CONSERVATIVE MUTATION
amino acid is replaced by one with different properties

NO MUTATION
in many cases a change in the third position of the codon does not change an amino acid

Question 17

Effects of insertion/deletion

Answer 17

Causes a frame-shift, hence synthesis of a protein that has a completely different sequence downstream of the mutation

-If any of these changes introduces or removes a stop codon - premature or delayed termination occurs

Question 18

What diseases can be caused by single base substitution

Answer 18

-Dementia
-Sickle cell anaemia (GAG to GTG)