Transcription Flashcards
(11 cards)
Overview of transcription and translation
- For a cell to perform its function, there must be a protein performing the task
- All information about the production of proteins is stored in the DNA.
- Protein synthesis - the creation of protein:
DNA is transcribed into mRNA in the nucleus.
- mRNA is transported to a ribosome.
- mRNA is translated into a polypeptide in the ribosome with help of tRNA.
- The polypeptide is folded into a protein. (amino acids chain)
DNA transportation:
DNA section has information about a specific protein - called a gene.
DNA stored in the nucleus.
This information needs to be transported to the cytoplasm where the ribosomes are.
Transported by: mRNA (messenger RNA).
Process of transcription
- Enzyme RNA Polymerase, attaching to the binding site at the start of the gene.
- RNA polymerase unwinds the double stranded DNA and separates the strands into single strands.
- RNA polymerase moves along the template strand.
- RNA polymerase puts free RNA nucleotides, complementary to the bases of DNA template strand.
- RNA polymerase links the RNA nucleotides together with covalent bonds.
- At stop sequence RNA, RNA polymerase detaches from DNA, allowing the double helix to reform.
Newly formed RNA
Informaiton of newly formed RNA molecule, is identical to the informaiton of the sense strand (coding strand) of the DNA.
Thymine replaced with Uracil.
Template strand used for RNA synthesis is also called antisense strand.
DNA molecule remains the same after the transcripion as before.
Gene expression
All cells have the same DNA.
Only the genes needed are transcribed to produce proteins.
Transcriptions, genes are switches on or off.
The RNA present in a cell is its transcriptome.
Proteins are proteome.
Nitrogenous base
A, G, C, U, T
3 of them make up an amino acid.
Codon - 3 nitrogenous bases
mRNA
In its order of nitrogenous bases, it codes for a specific sequuence of amino acids in the polypeptide.
Has a sequence where ribosomes can bind.
Also has a stop and a start codon - where translation starts and ends.
After usage, mRNA is recycled into nucleotides. But the sequence that it si already in, can be used many times.
tRNA
translates base sequence of mRNA into an amino acid sequence.
64 tRNA, one for each possible anticodon
Each tRNA has a binding site to a specific amino acid. An activation enzyme recognises the the shape of the tRNA and attaches the correct amino acid.
Ribosomes
Organelles that are either free in the cytosol or attached to the rough ER.
Ribosomes are made out of protein and rRNA - ribosomal RNA.
Two subunits:
Small subunit - A binding site for rRNA
Large subunit
- three binding sites for tRNA.
- Catalyctic site that makes peptide bonds between amino acids.
codons
20 amino acids require codons of three bases (triplet)
Translation ribosomes
Amino acids are attached to tRNA by an activation enzyme.
tRNA binds to the A-site of ribosome. It forms hydrogen bonds between complementary bases of the codon to the anticodon of tRNA
Peptide bonds are formed between amino acids in the A-site and amino acid in the P-side.
