1.4 (protein synthesis) : biological molecules

Question 1

compare Eukaryotic vs Prokaryotic DNA

Answer 1

• Eukaryotic dna is linear whereas Prokaryotic dna is circular
• Eukaryotic dna is associated with histone proteins whereas Prokaryotic dna is not

Question 2

what are introns?

Answer 2

non coding DNA base sequences found within a gene

Question 3

contrasting DNA and mRNA

Answer 3

• DNA is double stranded whereas mRNA is single stranded
• DNA is longer whereas mRNA is shorter
• DNA has thymine whereas mRNA has uracil instead
• DNA has a deoxyribose sugar whereas mRNA has a ribose sugar
• DNA has hydrogen bonds whereas mRNA does not.
  -DNA has introns whereas mRNA does not

Question 4

what is a genome

Answer 4

complete set of genes in a cell

Question 5

what is a loci

Answer 5

position of a gene within chromosomes

Question 6

what is an allele

Answer 6

a different version/ form of a gene

Question 7

what is a gene

Answer 7

• a DNA base sequence that codes for a sequnce of amino acids in a polypeptide

Question 8

where does transcription occur in prokaryotes and eukaryotes

Answer 8

prokaryotes: in the cytoplasm
eukaryotes: in the nucleus

Question 9

which molecule is formed during transcription

Answer 9

pre-mRNA

Question 10

What does it mean by splicing the pre-mRNA

Answer 10

introns are removed and exons are re-joined to form mature mRNA used in translation

Question 11

describe transcription

Answer 11

1- DNA helicase breaks hydrogen bonds so strands can separate
2- ONLY ONE strand acts as a template
3- RNA nuceoltides attracted to exposed bases
4- attraction according to base pairing rule Adenine-Uracil , Cytosine-Guanine
5- RNA polymerase joins (RNA) nucleotides together forming phosphodister bonds through condensation reactions
6- Pre-mRNA spliced to remove introns (in eukaryotics)

Question 12

describe translation

Answer 12

1- mRNA binds to ribosome
2- ribosome finds the start codon
3- there are TWO codons/binding sites
4- allows tRNA with complementary anticodons to bind with codon
5- catalyses formation of peptide bond between amino acids (held by tRNA molecules) using energy from ATP
6- tRNA released as ribosome moves along mRNA to the next codon
7- ribosome releases polypeptide into RER when the STOP codon is reached

Question 13

what are the three terms to describe 3 bases on
DNA
mRNA
tRNA

Answer 13

• DNA triplet
• mRNA codon
• tRNA anticodon

Question 14

why is the genetic code universal in transcription and translation

Answer 14

the same 3 bases on mRNA(codon) code for the same amino acids in all organisms

Question 15

non- overlapping genetic code?

Answer 15

each base is only part of 1 triplet(DNA) / codon(mRNA)

Question 16

degenerate genetic code?

Answer 16

more than one triplet for each amino acid

Question 17

what is a mutation

Answer 17

any change to the DNA base sequence

Question 18

what is a gene mutation(single point mutation)

Answer 18

• a change to a single base in the DNA base sequence of a gene
• can occur randomly and happen spontaneoulsy

Question 19

what is a substitution mutation

Answer 19

• a silent mutation
• does not change the amino acid coded for so will have no effect

Question 20

what are addition/deletion mutations

Answer 20

• 1 full DNA nucleotide base is gained or lost
• base triplet from the mutation onwards is altered
• which causes a frameshift

Question 21

what happens when a mutation causes a triplet to code for a STOP CODON

Answer 21

• growing polypeptide chain will terminate prematurely

Question 22

what is natural selection

Answer 22

• process by which organisms that are better adapted to their environment survive and reproduce in greater numbers
• resulting in the increase of the FREQUENCY of the advantageous allele within the population

Question 23

explain how selection occurs in living organisms

Answer 23

1- variation due to mutation
2- different environmental conditions
3- selection for different characteristics
4- differential reproductive success
5- leads to change in allelic frequency
6- occurs over a long period of time