Unit 1- Transcription And Translation Flashcards
Where does translation occur?
At the ribosomes
Where does transcription occur?
In the nucleus
How many tRNA can diffuse into the ribosome at once?
2
What do ribozymes do?
They catalyse the reactions on going in the ribosome
Eg, forming the peptide bond, cutting the bond between the amino acid and tRNA
Describe the process of translation
- Ribosome attaches to mRNA at initiation codon
- The first tRNA molecule with amino acid attached diffuses into ribosome
- the tRNA anticodon binds to the codon of the mRNA
- the next amino acid tRNA attaches to the adjacent mRNA codon
- the bond between the amino acid and tRNA is cut by ribozymes and a peptide bond forms between amino acids
- the ribosome moves along to the next codon so a new amino acid tRNA can attach
- this repeats until a stop codon is reached, the ribosome falls apart
Structure of tRNA
Strand of RNA, shaped like a clover with disulphide bonds
One end has anticodon and other has the amino acid that is coded from the codon
Where does RNA polymerase bind to on the DNA?
A specific sequence of bases called promoters at the start of a gene
What is the antisense strand?
This is the template strand that is complementary to the new mRNA
What is the RNA sense sequence?
This is the sequence of bases on RNA that code for proteins
What does RNA polymerase do?
Catalyses the formation of strong covalent phosphodiester bonds between RNA nucleotides
What are cut out in splicing?
Introns
Describe the process of translation up to pre-RNA
- RNA polymerase binds to DNA at promoter sequence
- RNA polymerase is a bundle of enzymes, one of these, helicase unwinds the DNA double helix
- this forms a transcription bubble (8 nucleotides long)
- one of the open strands is the template strand where ribose nucleotides join by complementary base pairing
- the RNA nucleotides are joined by covalent bonds by RNA polymerase
- RNA polymerase moves along the DNA, unwinding in front and rewinding behind
- the RNA polymerase stops transcription when it reaches the end of the gene
Where does mature RNA go?
Into the cytoplasm to find a ribosome through the nuclear pore
Why do prokaryotes not need spliceosomes?
They contain no introns in their DNA
What is post translation modification?
Proteins have been made but aren’t functional so they need to be modified slightly
Give an example of post translation modification
Chain cutting
Adding methyl or phosphate groups to some amino acids
- adding sugars and lipids -> glycoproteins and lipoproteins
What is it called when a single piece of mRNA has many ribosomes attached at once
Polyribosome
What are the 3 types of gene mutation?
Deletion
Substitution
Insertion
What are gene mutations?
Changes in DNA base sequences due to base pairing errors
When do gene mutations occurs?
DNA replication
How many amino acids does substitution affect?
1
What is a silent mutation?
When the mutation doesn’t affect the amino acid it codes for, due to amino acids being degenerate
Or it occurs in introns which don’t code for proteins anyway
What is a nonsense mutation?
When a substitution mutation produces a stop codon, causing an incomplete nonfunctional protein
Why are deletion and insertion more serious mutations?
- frame shift
- where all the amino acids being coded are wrong
What is affected by gene mutation in sufferers of sickle cell anemia?
A substitution in one of the haemoglobin polypeptide chains causes the haemoglobin to shape differently also mutating the shape of the red blood cell
