RNA and protein synthesis Flashcards
Describe the structure of messenger RNA (mRNA)
- A long single polynucleotide strand
- Its base sequence is complementary to the DNA it was transcribed from
Suggest advantages of using mRNA rather than DNA for translation
- Shorter and contains uracil so breaks down quickly so no excess polypeptide forms
- Single-stranded and linear so ribosome moves along strand and tRNA binds to exposed bases
- Contains no introns
Describe the structure of transfer RNA (tRNA)
- A single polynucleotide strand
- Folded over into a clover leaf shape, hydrogen bonds between base pairs hold the molecule in the shape
- Has an anti-codon on one end and on the opposite is an amino binding site
What is produced by transcription
mRNA
Where does transcription take place
In the nucleus
Outline the process of transcription
- DNA helicase unwinds double helix, to produce exposed DNA bases and 1 template strand
- Hydrogen bonds between DNA bases break
- 1 template strand is used to make an mRNA copy
- free-floating RNA nucleotides line along exposed DNA bases on the template strand, they are attracted via specific complementary base pairing
- Uracil binds to adenine
- RNA polymerase joins adjacent RNA nucleotides
- RNA polymerase reforms phosphodiester bonds
- When RNA polymerase reaches a stop signal, it detaches from DNA
What happens to mRNA after transcription
Pre-mRNA must be spliced to remove introns, leaving only the coding regions so then it moves out of the nucleus via the nuclear pores and attaches to a ribosome
What is produced by translation
Protein
Where does translation take place
On ribosomes in the cytoplasm
Outline the process of translation
- mRNA attaches itself to a ribosome and tRNA molecules carry amino acid molecules to it
- ATP provides the energy needed for the bond between the amino acid and tRNA molecule to form
- tRNA carries the amino acid with an anticodon that’s complementary to the first codon on the mRNA and attaches itself via complementary base pairing
- A second tRNA molecule attaches itself to the next codon
- The 2 amino acids attached to the tRNA molecule are joined via a peptide bond, the first tRNA molecule moves away
- The third tRNA molecule binds to the next codon on the mRNA, its amino acid binds to the first two and then it moves away
- Continues until stop signal
Describe the differences in transcription between eukaryotes and prokaryotes
- In eukaryotes the introns and exons are both copied into mRNA during transcription, mRNA strands containing introns and exons are pre-mRNA. Then splicing occurs, introns are removed and exons join together, then the mRNA strand leaves the nucleus
- In prokaryotes, mRNA is produced directly from the DNA without splicing
Describe how the genetic code is degenerate
There are more possible combinations of triplets than there are amino acids so some amino acids are coded for by more than one base triplet
