protein synthesis Flashcards
Define the term exon.
Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure;
Describe Transcription in Eukaryotes
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- (Free) RNA nucleotides align by complementary base pairing;
- (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds (between adjacent nucleotides);
- Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
THINK - Key word is adjacent
Whenever you see transcription think RNA, RNA polymerase , Pre-mRNA -> mRNA
Describe Translation
- (mRNA attaches) to ribosomes OR (mRNA attaches) to rough endoplasmic reticulum;
- (tRNA) anticodons (bind to) complementary (mRNA) codons;
- tRNA brings a specific amino acid;
- Amino acids join by peptide bonds;
- (Amino acids join together) with the use of ATP;
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA to form the polypeptide;
THINK - Translation = a transition
So there is a transition from mRNA to tRNA
tRNA = anticodons & mRNA = codons
Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA).
- mRNA does not have hydrogen bonds / base pairing, tRNA does; OR mRNA is linear / straight chain, tRNA is cloverleaf;
- mRNA does not have an amino acid binding site, tRNA does;
- mRNA has more nucleotides;
- (Different) mRNAs have different lengths, all tRNAs are similar / same length;
- mRNA has codons, tRNA has an anticodon;
What is an allele?
(Different) form/type/version of a gene / different base sequence of a gene;
Explain how selection occurs in living organisms (5)
- Variation due to mutation;
- Different environmental/abiotic/biotic conditions / selection pressures;
- Selection for different/advantageous, features/characteristics/mutation/ /allele;
- Differential reproductive success / (selected) organisms survive and reproduce;
- Leads to change in allele frequency;
- Occurs over a long period of time;
Define degenerate code
More than one codon for one amino acid
Explain what the term non-overlapping DNA means.
A base from one triplet cannot be used in an adjacent triplet
A mutation in a gene coding for an enzyme
could lead to the production of a non-functional enzyme. Explain how
- Change in base sequence (of DNA/gene);
- Change in amino acid sequence / primary structure (of enzyme);
- Change in hydrogen/ionic/ disulphide bonds;
- Change in the tertiary structure/active site (of enzyme);
- Substrate not complementary/cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.
- Triplets code for same amino acid
- Occurs in introns /non-coding sequence;
Contrast Eukaryotic DNA and Prokaryotic DNA (3)
- Eukaryotic DNA is linear whereas Prokaryotic
DNA is circular - Eukaryotic DNA is associated with histones whereas Prokaryotic DNA is not associated with histones
- Eukaryotic DNA contains introns whereas
Prokaryotic DNA does not contain introns
Contrast DNA and mRNA (3)
- DNA is double stranded whereas RNA is
single stranded - DNA is longER whereas RNA is shortER
- Thymine in DNA whereas thymine is replaced with uracil in RNA
- Deoxyribose in DNA whereas ribose in RNA
- DNA has hydrogen bonds whereas mRNA doesn’t have hydrogen bonds
- DNA has introns whereas mRNA doesn’t have introns
Explain what the term non - overlapping means (1)
a base from one triplet cannot be used in an adjacent triplet
Define what is meant by
Universal code
the same three bases on mRNA/DNA code for the same amino acids in all organisms
Describe what happens when the third base of a triplet is altered (2)
- Silent mutation so it will not change the amino acid coded for
- so will have no effect on the polypeptide chain
- code is degenerate so more than one codon can code for the same amino acid
Describe what happens when the first base of a triplet is altered (3)
- will change the amino acid coded for
- alters the sequence of amino acids on polypeptide chain
- may alter the specific tertiary structure
Describe the effect of an addition/deletion mutation towards the end of a sequence of bases. (2)
- reading frame has been shifted to right/left so causes a frame shift
- lesser effect but would still alter some amino acids at end of gene
Explain the effect of an addition/deletion mutation at the start of a sequence of bases. (2)
- reading frame has been shifted to right/left so causes a frame shift
- all triplets coding for polypeptide would be altered so all amino acids would be altered
Name 3 types of mutagenic agents and give 2 examples for each
- High energy ionising radiation - X rays and gamma rays
- DNA reactive chemicals - benzene and bromine
- Biological agents - viruses and bacteria
Name 3 chromosomal mutations
- Inversion Mutations
- Duplication Mutations
- Translocation Mutations
What happens during an inversion mutation? (1)
a segment of bases is reversed end to end
What happens during a duplication mutation? (1)
a doubling part of a chromosome, of an entire chromosome, or even the whole genome - a section of DNA is duplicated
What happens during a translocation mutation? (1)
groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes
Describe the difference between stabilising selection and directional selection (1)
Stabilising selection favours the average whereas directional selection favours an
extreme phenotype
