D1.2 Protein synthesis Flashcards
(35 cards)
What is transcription?
The synthesis of RNA using DNA as a template
What are the 3 forms of RNA?
mRNA
rRNA
tRNA
What is mRNA? (messenger)
the strand that is complementary to 1 strand of the DNA molecule (template strand), copy of other DNA strand
What is rRNA? (ribosomal)
Found in ribosomes, decodes mRNA into amino acids
What is tRNA? (transfer)
Carries amino acids to the ribosomes where they are bonded together to form polypeptides
Where does transcription take place for eukaryotic cells?
Cell nucleus
Where does transcription take place for prokaryotic cells?
Cytoplasm
What are the 3 stages of transcription?
Initiation stage:
RNA polymerase binds to DNA at the start a gene, separates 2 strands of DNA (breaking hydrogen bonds), exposes bases
Elongation stage:
RNA polymerase builds molecule of mRNA on one of the strands of DNA (antisense)
Termination stage:
A terminator sequence is reached, mRNA released
What does RNA polymerase do?
Separates the strands (like helicase), transcribes DNA into RNA
What is the antisense/ template strand?
RNA polymerase building a molecule of mRNA on one of the strands of DNA
What is the difference between DNA and mRNA?
- mRNA single stranded
- mRNA has ribose
- mRNA has Uracil not thymine
The DNA’s base triplets are converted into mRNA ……… during transcription
Codons
What is translation?
Process in which the transcribed RNA is translated by the ribosomes to produce proteins
What happens during translation?
- mRNA transcribed, moves out of the nucleus via nuclear pore
- In cytoplasm, mRNA combines with a ribosome
What are the 3 stages in transcription?
Initiation
Elongation
Termination
How does translation work?
- mRNA attaches to the ribosome at the ‘start’ codon (AUG)
- tRNA with a complementary anticodon attaches to mRNA (UAC)
- This tRNA os attached to an amino acid (methionine)
- Ribosome moves along mRNA bringing in 2 tRNA molecules at any 1 time
- Enzyme & ATP are used to join the amino acids with a peptide bond
- tRNA released & can collect another amino acid
- Process repeats until ‘stop’ codon is reached
What is an anticodon?
Complementary codons on the mRNA molecule
What are some structural characteristics of tRNA?
- single stranded, folded into a clover leaf shape (one end slightly longer)
- longer section is added to an amino acid
What happens in the elongation stage?
ribosomes move along the mRNA, one codon at a time, as new amino acids are delivered, condensation reactions are catalysed & peptide bonds formed between them
What is the genetic code?
The sequence of bases along its DNA, which contains thousands of sections called genes / cistrons
What are some key information about the genetic code?
- sequence of nucleotides on a gene
- triplet code
- non-overlapping
- degenerate
- universal
What is a mutation?
When a mistake is made synthesising DNA or RNA
What is a point mutation?
Involves the deletion, addition or replacement of a single nucleotide (can occur in both DNA replication & transcription)
What is a frameshift mutation?
Where all of the codons following that mutation are altered as there is a shift in the base sequence
