PROTEINS Flashcards
What is transcription?
Production of mRNA from DNA.
What is the process of transcription?
• DNA strand unwinds and unzips by DNA helicase
• Instead of a new DNA strand being formed, RNA nucleotide bases pair up with the exposed
DNA bases
• An enzyme called RNA polymerase forms covalent bonds between the nucleotide bases
• Unlike DNA, RNA is single-stranded
• A messenger RNA (mRNA) strand is formed and breaks away from the DNA which then rezips
itself up thanks to the natural formation of hydrogen bonds
6. mRNA is now free to migrate out of the nucleus through nuclear pores
What enzyme unzips DNA strand?
DNA helicase
What is the purpose of the enzyme RNA polymerase?
RNA polymerase forms covalent bonds between the nucleotide bases
How does the mRNA leave the nucleus?
Through the nuclear pores
How does DNA differ from RNA?
It is single stranded
What forms covalent bonds between nucleotide bases?
Enzyme called RNA poylermase
What does a gene code for?
- Amino acid sequence of a polypeptide
* A functional RNA ( including ribosomal RNA and tRNAs )
Where is a gene present?
A gene occupies a fixed position called a locus on a DNA molecule.
What is a triplet?
Sequence of three DNA bases
What does a triplet do?
codes for a
specific amino acid
What are some features of triplets?
The genetic code is universal, non-overlapping
and degenerate.
What is the genome?
Complete set of genes in a cell
What is the proteome?
Full range of proteins that a cell is able to produce
What is the purpose of RNA polymerase?
Joining mRNA nucleotides
What does transcription result in in prokaryotes?
Transcription results in the production of mRNA from DNA
What does transcription result in, in eukaryotes?
Transcription results in the production of pre-mRNA, that is spliced to form mRNA nucleotides
What is translation?
production of polypeptides from the sequence of codons carried by mRNA
What is the process of translation?
- Once mRNA has left the nucleus, it attaches to a ribosome on the rough endoplasmic
reticulum - Transfer RNA (tRNA) carries the corresponding amino acid to each on the mRNA
- The anti-codon is a triplet of bases that form part of a tRNA molecule and ensure that the
correct amino acid is joined onto the polypeptide chain - This process is active and requires ATP
- The amino acid transported by the tRNA attaches to the ribosome
- Adjacent amino acids join together by peptide bonds, creating a polypeptide chain
- This process continues until the ribosome reaches a ‘stop’ codon (triplet) on the mRNA. At
this point, the polypeptide breaks loose from the ribosome and is free.
What occurs in prokaryotic transciption?
• mRNA directly produced from DNA
What occurs in eukaryotic transcription?
• DNA is first copied into pre-mRNA
• May contain pieces of non-useful polynucleotide
• pre-mRNA is spliced into mRNA
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