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A2 Biology Unit 5 > Protein Synthesis > Flashcards

Flashcards in Protein Synthesis Deck (20):

What is transcription?

Transcription is the first stage of protein synthesis. During transcription an mRNA copy of a gene is made in the nucleus.


Why is mRNA in eukaryotic DNA edited?

Genes in eukaryotic DNA contain introns that don't code for amino acids


What are introns?

Sections of DNA that don't code for amino acids


What are extrons?

Sections of DNA that code for amino acids


What is pre-mRNA?

mRNA strands containing introns and extrons


What happens during splicing?

Introns are removed from pre-mRNA and extrons joined together to form an mRNA strand


What is translation? Where does it take place?

It is the second stage of protein synthesis
It takes place in the ribosomes in the cytoplasm


What happens during translation?

Amino acids are joined together by a ribosome to make a polypeptide chain following the sequence of codons carried by the mRNA


Name the cell organelle involved in translation.



What is the role of RNA polymerase in transcription?

Join nucleotides, to form a strand/along backbone


Explain how a change in the base sequence of the mRNA could lead to a change in the tertiary structure of the toxin.

Different primary structure / amino acid sequence / amino acid coded for.


Give two differences between the structure of mRNA and the structure of tRNA.

mRNA has no base-pairing & tRNA has base-pairing
mRNA linear & tRNA cloverleaf shape
mRNA has no binding site for amino acids & tRNA


Explain how DNA replicates

Hydrogen bonds broken
Semi-conservative replication
Nucleotides line up
Complementary / specific base pairing / A and T / C and G
DNA polymerase


Starting with mRNA in the nucleus of a cell, describe how a molecule of protein is synthesised.

1. mRNA leaves (nucleus) through nuclear pore;
2. To ribosome;
3. tRNA molecules bring amino acids (to ribosome);
4. Specific tRNA molecule for specific amino acid;
5. Anticodon of tRNA corresponds / complementary to codon on mRNA; 6. Peptide bonds form between amino acids;
7. tRNA detaches and collects another amino acid;
8. Ribosome moves along mRNA;


Starting with mRNA, describe how the process of translation leads to the production of a polypeptide.

mRNA attaches to ribosome.
Codon on mRNA.
Binds to an anti-codon on tRNA.
Each tRNA brings a specific amino acid.
Sequence of codons determines order of amino acids. Formation of peptide bonds/amino acids joined by condensation reactions.


Describe the role of RNA polymerase in transcription.

Moves along template DNA strand, causing the bases on this strand to join with the individual complementary nucleotides from the pool that is present in the nucleus.
Until a stop codon is reached.


Why is splicing of pre mRNA necessary?

Splicing is necessary because pre mRNA has nucleotide sequences derived from from introns in DNA.
These introns are non functional and, if left on mRNA, would lead to non functional polypeptides.
So they're removed.


Describe the role of DNA helicase in transcription.

This acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases, causing the two strands to separate and expose the nucleotide bases.



Enzyme DNA helicase acts on a specific region of DNA to break h bonds between bases causing strands to separate.
Enzyme RNA polymerase moves along template strand causing nucleotides to join with complementary nucleotides.
DNA strands form behind it and pre-mRNA is made.
When RNA polymerase meets a stop codon it detaches.



The ribosome binds to mRNA at a specific area.
The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.
Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain as a result of an enzyme + ATP.
Stops once a stop codon is reached.