DNA and Protein Synthesis Flashcards
What are the two main processes in protein synthesis?
Transcription and translation
Where does transcription occur?
What does it involve?
In the nucleus
Involves ‘rewriting’ (transcribing) part of the DNA code into a strand of messenger RNA
Where does translation occur?
What does it involve?
In the cytoplasm
Involves ribosomes synthesising proteins using the information provided by messenger RNA
What does transcription make?
mRNA using DNA as a template
What does translation make?
A polypeptide using mRNA, tRNA and ribosome
What are the steps of transcription?
1- Hydrogen bonds are broken -> DNA uncoils
2- One strand = the template
3- RNA nucleotides line up alongside the DNA bases due to complementary base pairing
4- Adenine is complementary to Uracil and Guanine is complementary to Cytosine
5- Base sequence in mRNA is the same as the non-template strand
6- Individual RNA nucleotides joined together by phosphodiester bonds in reactions catalysed by RNA polymerase -> polynucleotide strand of mRNA
7- DNA recoils in nucleus when sufficient mRNA is produced
8- mRNA undergoes splicing and leaves nucleus (eukaryotes)
9- mRNA attaches to a ribosome in the cytoplasm where translation occurs.
What does splicing of pre-mRNA do?
Removes introns
What is DNA of a gene made up of in eukaryotes?
Exons and introns
What does the splicing of pre-mRNA involve?
The removal of introns and the joining together of the exons to form mRNA
Why does splicing not occur in prokaryotes?
Their DNA does not contain introns
What happens to spliced mRNA strand?
It leaves the nucleus through the nuclear pore and attaches to a ribosome in the cytoplasm where translation occurs
What does RNA polymerase do?
-Catalyses condensation reactions between RNA nucleotides.
- Joins the RNA nucleotides together by strong phosphodiester bonds to produce a polynucleotide chain of pre-mRNA
What is used to make a polypeptide?
mRNA, tRNA and rRNA
What happens to the sequence of codons on the mRNA strand in translation?
They are sued to determine the sequence of amino acids in a polypeptide
How many codons can a ribosome fit on it?
Only two
What are the steps of translation?
1- The mRNA binds to a ribosome in the cytoplasm
2- A tRNA molecule ,carrying an apricot amino acid, with the complementary anticodon base sequence binds to the first codon on the mRNA strand at the ribosome. The ribosome has two binding sites so that two tRNA molecules will bind to two codons on the mRNA within a ribosome.
3- The specific amino acids on the first tRNA molecule attaches to the amino acid on the second tRNA molecule by a peptide bond in a condensation reaction. This requires hydrolysis of ATP to release energy and an enzyme that is part of the ribosome.
4- The first tRNA molecule then moves away from the ribosome, leaving the amino acid behind. It collects another molecule of the same specific amino acid from the ‘amino acid pool’ in the cytoplasm
5- The ribosome moves along the mRNA and other tRNA molecules then join in the order determined by the codons on the mRNA strand.
6- This process continues along the mRNA strand until all the codons have been ‘read’ up to the stop codon and the specific polypeptide has been produced.
Where is the ‘amino acid pool’ located?
In the cytoplasm
What is the sequence of amino acids in the polypeptide determined by?
The codons on the mRNA strand
What happens as mRNA is transcibed from DNA?
The sequence of DNA nucleotides that ultimately determines which specific polypeptide is produced
