DNA, RNA and Protein Synthesis- RNA and Protein Synthesis Flashcards
How is RNA different to DNA?
It is a single polynucleotide and contains uracil instead of thymine
What does uracil pair with?
Adenine
What are the 2 main types of RNA?
Messenger RNA (mRNA) and transfer RNA (tRNA)
When is mRNA made?
During transcription
What is the role of mRNA?
Carries the genetic code from the DNA to the ribosomes where it is used to make a protein during translation
What is the structure of mRNA?
Single polynucleotide strand, contains codons
What are codons?
Groups of 3 adjacent bases
What is tRNA involved in?
Translation
What is the role of tRNA?
Carries the amino acids that are used to make proteins to the ribosomes
What is the structure of tRNA?
Single polynucleotide strand folded into a clover shape- held in shape by hydrogen bonds between specific base pairs
What does every tRNA molecule have?
A specific sequence of 3 bases at one end called an anticodon and an amino acid binding site at the other end
What happens during transcription?
An mRNA copy of a gene is made from DNA
Where does transcription take place in eukaryotes?
The nucleus
Where does transcription take place in prokaryotes?
The cytoplasm
How does transcription start?
When RNA polymerase attaches to the DNA double helix at the beginning of a gene
What is the role of DNA helicase?
Breaks the hydrogen bonds between DNA strands which separates the strands and causes DNA molecule to unravel, exposing some bases
What is the purpose of one strand being used as a template?
To make an mRNA copy
What is the role of RNA polymerase?
Lines up free RNA nucleotides alongside the exposed bases on the template strand and the free bases are attracted to the exposed bases
What does complementary base pairing mean?
mRNA strand ends up being a complementary copy of the DNA template strand
What happens once the RNA nucleotides have paired up with their specific bases on the DNA strand?
They’re joined together by RNA polymerase to form an mRNA molecule
What does the RNA polymerase do once the mRNA molecule is formed?
Moves along the DNA to separate the strands and assemble the mRNA strand
When do the hydrogen bonds between the uncoiled strands of DNA re-form?
Once the RNA polymerase has passed by and the strands coil back into a double helix
What happens when RNA polymerase reaches a stop signal?
It stops making mRNA and detaches from DNA
What happens in eukaryotes to allow the next stage of protein synthesis to take place?
mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm
What is the process of transcription?
- RNA polymerase attaches to DNA double helix at the beginning of a gene
- Hydrogen bonds between the 2 DNA strands in the gene are broken by a DNA helicase attached to the RNA polymerase which separates the strands and the DNA molecule uncoils, exposing some bases
- One strand used as a template to make an mRNA copy
- RNA polymerase lines up free RNA nucleotides alongside the exposed bases on template strand, free bases are attracted to exposed bases, complementary base pairing means mRNA strand ends up being a complementary copy of DNA template strand
- Once RNA nucleotides have paired up with specific bases on DNA strand, they’re joined together by RNA polymerase, forming an mRNA molecule
- RNA polymerase moves along DNA, separates strands and assembles mRNA strand
- Hydrogen bonds between uncoiled strands of DNA re-form once RNA polymerase has passed by and strands coil back into a double helix
- When RNA polymerase reaches stop signal, stops making mRNA and detaches from DNA
- mRNA moves out nucleus through nuclear pore and attaches to a ribosome in cytoplasm
What is pre-mRNA?
mRNA strands that contain exons and introns
What is splicing?
Introns are removed from pre-mRNA
What is produced in prokaryotes from transcription?
mRNA is produced directly without introns
What is the final stage of transcription?
Pre-mRNA is spliced to make mRNA without introns
Where does translation occur?
At the ribosomes in the cytoplasm
What happens during translation?
Amino acids are joined together to make a polypeptide chain following the sequence of codons carried by the mRNA
What does tRNA do when mRNA attaches itself to a ribosome?
Carries amino acids to it
What is the role of ATP in translation?
Provides the energy needed for the bond between the amino acid and the tRNA molecule to form
How does a tRNA molecule attach itself to mRNA?
Specific base pairing- the anticodon on the tRNA is complementary to the codon on the mRNA
What happens after one tRNA molecule has attached to the mRNA molecule?
A second tRNA molecule attaches to the next codon
How are the two amino acids attached to the tRNA molecule joined?
By a peptide bond- first tRNA molecule moves away and the amino acid is left behind
When does the process of tRNA molecules bonding to codons stop?
When there’s a stop signal on the mRNA molecule
When is translation complete?
The polypeptide chain moves away from the ribosome
What is the process of translation?
- mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it, ATP provides energy needed for the bond between the amino acid and the tRNA molecule to form
- tRNA molecule with an anticodon that’s complementary to the first codon on mRNA, attaches to mRNA by specific base pairing
- Second tRNA molecule attaches to next codon on mRNA in same way
- Two amino acids attached to tRNA molecules are joined by a peptide bond, first tRNA molecule moves away and leaves amino acid behind
- Third tRNA molecule binds to next codon on the mRNA, amino acid binds to first two and second tRNA molecule moves away
- Process continues, produces a chain of linked amino acids (polypeptide chain) until stop signal reached on mRNA molecule
- Polypeptide chain moves away from ribosome and translation is complete
