Protein synthesis Flashcards
Define the term exon
A base sequence coding for a polypeptide
Describe transcription in eukaryotes.
-hydrogen bonds between bases are broken
- only one strand is used as a template
- free RNA nucleotides bind to exposed bases accordingly to base pairing rules
- uracil to adenine and cytosine to guanine
-RNA polymerase joins adjacent nucleotides up with phosphodiester bonds
-pre MRNA is spliced to remove introns
Describe translation
-MRNA strand binds to ribosome
-anticodons on tRNA complementary to codons on mRNA
-TRNA brings specific amino acid
-peptide bonds form between amino acids
- using atp
- TRNA is released
- ribosome moves along the MRNA forming the polypeptide
Give two structural differences between mRNA and tRNA
- mRNA is linear whereas tRNA is clover leaf shaped
-mRNA has codons whereas tRNA has anticodons
What is an allele?
A version of a gene
Explain how selection occurs in living organisms. 6 marks
- mutation causes variation
- selection pressures such as predators
-mutation gives individual an advantage against selection pressures so survive
-survives so reproduces passing down advantageous allele to offspring
-over a long time
-causes a change in allele frequency
Define degenerate code
Many codons code for the same amino acid
Explain what the term non overlapping DNA means
Base from one triplet can not be used in an adjacent triplet
A mutation in a gene coding for an enzyme could result in a non functioning enzyme. Explain how. 5 marks
-change is base sequence
- change in primary sequence
- causes different hydrogen, covalent and disulphide bonds to be formed in different places
- resulting in a different tertiary structure
-this changes the active site so is no longer complementary to substrate
- no enzyme substrate complexes can be formed
Not all mutation in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.
-mutation occurred within an intron
-more than one triplet code for the same amino acid
