Protein Synthesis Flashcards
1
Q
Describe transcription
A
- DNA is unwound by helicase by breaking the hydrogen bonds between fomplementary base pairing
- complementary copy of the coding sequence is made from mRNA using one strand of DNA as a temple. Joined by RNA polymerase catalysing the formation of phosphodiester bonds
- always 5’ -> 3’
- splicing occurs
- mRNA leaves nucleus
2
Q
Describe splicing
A
- only in eukaryotes- in prokaryotes, transcription directly produces mRNA from DNA
- splicozomes stade either end of an intron and splice it out, resulting in mature mRNA
3
Q
What is a splicozome?
A
Small nuclear ribonucleoproteins (SnRNPs)
4
Q
Describe translation
A
- mRNA leaves nucleus and attached to non-membrane-bound ribosome in the cytoplasm
- binds to a small subunit
- 1st amino acid always AUG (start codon) = Met
- in cytoplasm there are 64 different molecules of tRNA each with a specific triplet anticodon
- each tRNA has a specific amino acid attached by a specific amino-acyl tRNA synthétase enzyme
- process uses ATP and forms activated molecule to provide energy for peptide bond
- the anticodon of the correct tRNA then pairs with the codon of the mRNA
- this brings two tRNAs together in the ribosome and allows a peptide bond to form between the 2 amino acids by peptidyl transferase
- continues until a stop codon is reached (UAA, UAC, UGA)
5
Q
What is a ribosome made out of?
A
- rRNA
* protein
6
Q
Describe gene mutations
A
- DNA encodes for proteins and therefore a mutation (change in DNA sequence) may lead to a change in protein sequence
- change in a base pair within a DNA sequence of a gene can result in an altered or mutant gene product (protein)
- such a point mutation can result in a protein of altered function or a protein which lacks function altogether
- the majority of such mutations are disadvantageous or even lethal
- some mag be neutral or beneficial
7
Q
Why do gene mutations occur?
A
- can occur spontaneously during replication
* can be caused by mutagenic agents
8
Q
Why do chromosome mutations occur?
A
• can occur spontaneously by chromosome non-disjunction during meiosis/crossing-over errors
9
Q
Describe substitution
A
change of nucleotides
10
Q
Describe addition/insertion
A
Addition of an extra nucleotide
11
Q
Describe deletion
A
Loss of nucleotide(s)
12
Q
Describe inversion
A
Region breaks off, rotates 180° and then rejoins
13
Q
Describe duplication
A
- production of one or more copies of a gene or region of a chromosome
- occurs in all organisms- especially prominent among plants
- important mechanism by which evolution occurs
14
Q
Define missense
A
Change in amino acid residue
15
Q
Define nonsense
A
Change to stop codon
