DNA, RNA and Protein Synthesis - RNA and Protein Synthesis Flashcards
What are the two stages of protein synthesis called?
Transcription and translation.
Both involve RNA.
When is mRNA made?
What is its role?
mRNA carries the genetic code from the DNA to the ribosomes,
where it’s used to make a protein during translation.
It is made during transcription.
What is mRNA?
mRNA is messenger RNA.
It is a single polynucleotide strand.
In mRNA, groups of three adjacent bases are usually called codons (or triplets or base triplets).
What process is tRNA involved in?
What is its role?
Translation.
It carries the amino acids that are used to make proteins to the ribosome.
What is tRNA?
How is its shape held?
A single polynucleotide strand that’s folded into a clover shape.
Hydrogen bonds between specific base pairs hold the molecule in this shape.
Every tRNA molecule has a specific sequence of three bases at one end called an anticodon.
They also have an amino acid binding site at the other end.
Explain the process of transcription.
During transcription, an mRNA copy of a gene is made from DNA.
In eukaryotic cells, this takes place in the nucleus.
(In prokaryotes it’s the cytoplasm.)
1) Starts when DNA polymerase (an enzyme)
attaches to the DNA double-helix at the beginning of a gene.
2) Hydrogen bonds between the two DNA strands in the gene break, separating the strands, and the DNA molecule uncoils at that point, exposing some of the bases.
3) One of the strands is then used as a template to make an mRNA copy.
4) The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand.
The free bases are attracted to the exposed ones.
Specific, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand (except T replaced with U in RNA).
5) Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they’re joined together by RNA polymerase, forming an mRNA molecule.
6) The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand.
7) The hydrogen bonds between the uncoiled strands of DNA reform once the RNA polymerase has passed by and the strands coil back into a double-helix.
8) When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA.
9) In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place.
Explain the process of translation.
1) mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it.
ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form.
2) A tRNA molecule (carrying an amino acid) with an anticodon that’s complementary to the first codon on the mRNA attaches itself to the mRNA by specific base pairing.
3) A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
4) The two amino acids attached to the tRNA molecules are joined by a peptide bond.
The first tRNA molecule moves away, leaving its amino acid behind.
5) A third tRNA molecule binds to the next codon on the mRNA.
Its amino acid binds to the first two and the second tRNA molecule moves away.
6) This process continues, producing a chain of linked amino acids (a polypeptide chain), until there’s a stop signal on the mRNA molecule.
7) The polypeptide chain moves away from the ribosome and translation is complete.
