protein synthesis

Question 1

the genetic code is

Answer 1

triplet
universal
degenerate
non overlapping

Question 2

triplet code

Answer 2

Each three nucleotide codon in the mRNA specifies 1 amino in the poly peptide.

Question 3

non overlapping

Answer 3

Each nucleotide is part of only one codon and is read only once during translation

Question 4

degenerate

Answer 4

Most amino acids are coded for by more than one triplet of bases.

Question 5

almost universal

Answer 5

In most organisms each triplet codes for the same amino acid.

Question 6

triplet code

Answer 6

• If one base = one amino acid,
possible amino acids = 4
• If two bases = one amino acid, possible amino acids = 16 (4×4)
If three bases = one amino acid,
possible amino acids = 64 (4×4×4)

Question 7

eukaryote dna

Answer 7

• Eukaryotic DNA iS found in the nucleus.
• It is very long, linear DNA found as chromosomes when the cell is replicating.
• DNA associates with histones to form a DNA-histone complex which helps package and coil the DNA.

Question 8

prokaryote dna

Answer 8

• Prokaryotic DNA is much shorter in length and is circular in shape.
• Prokaryotes do not have a nucleus so it is found free in the cytoplasm.
• It is not associated with proteins.
• They may contain extra plasmid DNA.

Question 9

genome

Answer 9

The genome is the complete set of genes in a cell (including those in the mitochondria and chloroplast).

Question 10

proteome

Answer 10

The proteome is the full range of proteins produced by the genome. This can be known as the complete proteome, where the term proteome means the proteins made by a given type of cell under certain conditions.

Question 11

transcription

Answer 11

DNA helicase enzyme breaks hydrogen bonds between the bases in a specific region of DNA
The 2 double strands separate which exposes some nucleotide bases
RNA polymerase enzyme attaches to the template strand
The RNA polymerase moves along the template strand joining complementary free RNA nucleotides to the exposed DNA nucleotides.
As the RNA polymerase moves along the DNA, the DNA strands reform the double helix behind it.
When the end of the gene is reached, the RNA polymerase detaches and the pre-mRNA is released.
The pre-mRNA is spliced removing the introns and leaving only the exons to form mature mRNA.
The mature mRNA leaves the nucleus via nuclear pores and moves into the cytoplasm.

Question 12

processing mRNA

Answer 12

DNA contains some regions that do not code for proteins. These are known as introns.
To produce functional proteins these introns need to be spliced out of the mRNA, leaving only the regions that code for proteins, called exons.
A molecule called a spliceosome removes the introns, producing mature mRNA that contains only exons. Before splicing, mRNA is Known as pre-mRNA.

Question 13

translation

Answer 13

A ribosome in the cytoplasm becomes attached to a ‘start codon’ at one end of mRNA.
The tRNA with a complementary anticodon binds to the mRNA start codon in the ribosome. This carries a specific amino acid.
A second tRNA with a complementary anticodon to the next codon binds to the mRNA in the ribosome. This carries a specific amino acid.
A peptide bond forms between the two amino acids within the ribosome using an enzyme and ATP which is hydrolysed to provide energy.
The ribosome moves along the mRNA, one codon at a time bringing in another tRNA with its corresponding amino acid.
The first tRNA is released from the mRNA and is free to pick up another amino acid and be reused if needed.
This process happens across the mRNA until a ‘stop codon’ is reached. At this point the mRNA, ribosome and last tRNA dissociate and the polypeptide chain is formed.
The polypeptide is processed as necessary to form its secondary, tertiary and possibly quarternary structure