Protein Synthesis Flashcards
Name the pyrimidines
Thymine, Cytosine and Uricil
Two stages of protein synthesis
Transcription and then Translation
Name the purines
Adenine and guanine (all gods are pure)
What is a mutagenic agent
A agent that causes an increase the rate of mutation in a population e.g. High energy electromagnetic waves and chemicals that alter DNA
What is a mutation
A permanent random change in the sequence of nucleotides in a gene
What is somatic mutation ?
A mutation restricted to the body tissue of a single organism
What are the main differences between RNA and DNA?
- RNA is made of ribose nucleotides instead of deoxyribose
- RNA has U instead of T base
- RNA is single stranded but can fold into 3D structures
- RNA is much shorter
What are the 3 types of RNA?
Messenger, Transfer and Ribosomal
What is messenger RNA?
Carries the message that codes for proteins from the nucleus to the ribosomes in the cytoplasm
How many nucleotides long is a tRNA molecule?
80 Nucleotides long
What are the features of the structure of tRNA?
a 3 clover leaf structure, with an ACC sequence at one end where the amino acid binds. On the middle ‘loop’ there is a triplet nucleotide sequence called the ‘anticodon’ which is complementary to an opposite codon
How many kinds of tRNA are there?
64.
What enzyme attaches amino acids to tRNA?
tRNA Synthase
What does tRNA do?
Carries specific amino acids and transfers them to ribosomes for assembly of new polypeptides
What does it mean that the genetic code is ‘degenerate’?
There is often more than one codon which codes for an amino acid, cos there are 64 codons and 20 amino acids.
How is the genetic code ‘non-overlapping’?
Each base only contributes to a single codon. i.e. ACTGTT is ACT and GTT, not ACT, CTG, TGT etc.
What codon starts the gene sequence?
AUG
What direction is a gene read?
‘Downstream’, from 5’ to 3’.
Explain RNA Synthesis
- DNA gets unzipped to expose the bases
- trancription factors bind to the promoter codon to help fit the RNA polymerase into the DNA
- Ribose nucleotides attach themselves to the exposed bases of the template strand.
- joined together by covalent phosphodiester bonds by RNA polymerase on the 3’ end
- when transcription stops the mRNA diffuses out of the nucleus through the nuclear pores
Explain Translation/Protein Synthesis
- A ribosome attaches to the mRNA at the initiation codon (AUG)
- tRNA anticodon binds to the first mRNA codon by complementary base pairing
- the next amino acid-tRNA attaches to the mRNA codon by complementary base pairing
- peptide bonds are formed between the adjacent amino acids and the bond between the amino acid and the tRNA is cut.
- The ribosome moves along the mRNA so a new tRNA can attach and a new amino acid can be added to the new chain.
Which RNA molecule contains thymine
MWHAHAHA trick question, RNA molecules only ever contain uracil
Starting with mRNA, describe how the process of translation leads to the production of a
polypeptide.
mRNA attaches to ribosome; codon on mRNA; binds to an anti-codon on tRNA; each tRNA brings a specific amino acid; sequence of codons/bases on mRNA determines order of amino acids; formation of peptide bonds/amino acids joined by condensation reactions;
What is meant by a gene?
a length of DNA;
that codes for a single protein / polypeptide;
Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell.
It binds to promoter and stimulates RNA polymerase which
transcribes the gene/ increase transcription
Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body
Other cells do not have the oestrogen receptors
