Protein Synthesis

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  • Created by: zoolouise
  • Created on: 29-04-16 22:23
What is the definition of transcription?
Transcription is where one strand of the DNA acts as a template for the production of mRNA. It occurs in the nucleus.
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What is the definition of translation?
Translation is where the mRNA acts as a template for tRNA molecules, which carry amino acids to attach. It occurs on the ribosomes.
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What's the process of making a polypeptide from DNA?
DNA >translation in the nucleus> mRNA >translation at ribosome> Polypeptide
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What does the DNA act as a template as in transcription?
The DNA acts as a template for the production of mRNA and this leaves the nucleus and travels to the ribosomes in the cytoplasm.
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Where does transcription take place in eukaryotic and prokaryotic cells?
In eukaryotic cells it takes place in the nucleus, in prokaryotic cells it takes place in the cytoplasm.
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What are the steps of transcription (1)?
The enzyme DNA helicases breaks the hydrogen bonds between the bases in a specific region of the DNA molecule, this causes the two strands to seperate and unwind, exposing the nucleotide bases.
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What are the steps of transcription (2-3)?
2) Enzyme RNA polymerase binds to template strand of DNA at beginning of the sequence to be copied. 3) Free RNA nucleotides align oppsite template strand, based on complementary relationship between bases in DNA and the free nucleotides.
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What are the steps of transcription (4)?
4) RNA polymerase moves along DNA, forming bonds that add RNA nucleotides to growing RNA strand. Results in synthesis of mRNA. Behind the RNA polymerase, DNA strands rewind to reform double helix.
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What are the steps of transcription (5)?
RNA polymerase separates from the template strand when it reaches a 'stop' signl. The production of the transcript is complete, newly formed RNA detaches from the DNA.
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Where does translation occur in eukaryotes and prokaryotes?
It occurs at the ribosomes in the cytoplasm of both eukaryotes and prokaryotes and involves tRNA.
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What does a larger subunit have?
Two sites for the attachment of tRNA molecules, so two tRNA molecules are associated with a ribosome at one time
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What does a smaller subunit do?
Binds to the mRNA.
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What is the use of the sequences of codons on the mRNA?
They're used to generate a specific sequence of amino acids, forming a polypeptide.
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What does the ribosome act as?
A framework which moves along the mRNA, holding the codon-anti-codon together until two amino acids attached to adjacent tRNA molecules bind.
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What do ribosomes do as they move along the mRNA?
As ribosomes move along the mRNA they add one amino acid at a time until the polypeptide chain is assembled. The order of bases in DNA has therefore determined the order of amino acids in the polypeptide.
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What is initiation?
A ribosome attaches to a start codon at one end of the mRNA molecule.
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What does the first tRNA do after initiation?
The first tRNA with an anticodon complementary to the first codon on mRNA attaches to the ribosome. The 3 bases of the codon on the mRNA bind to their complementary bases of the anticodon on the tRNA, with hydrogen bonds
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What does a second tRNA do after initiation?
A second tRNA, with an anticodon complementary to the second codon on the mRNA, attaches to the other attachment site and the codon and antio-codon bond with hydrogen bonds
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What is elongation?
The two amino acids are sufficiently close for a ribosomal enzyme to catalyse the formation of a peptide bond between the two.
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What does the first tRNA do after elongation?
The first tRNA leaves the ribosome, leaving its attachment site vacant. It returns to the cytoplasm to bind to another copy of its specific amino acid. The ribosome moves one codon along the mRNA strand and the next tRNA binds.
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What is termination?
The sequence repeats until a 'stop' codon is reached
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What happens after termination?
The ribosome - mRNA - polypeptide complex separates
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What happens after the tRNA's released from the ribosome?
It's free to collect another amino acid from the cytoplasm.
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Why is energy needed?
To attach an amino acid to the tRNA, this comes from ATP and the process is called amino acid activation
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What happened in the 1940s?
Scientists experiments with a fungus called Neurospora crosa and it showed that radiation damage to DNA prevented a single enzyme from being made. They created the one gene - one polypeptide hypothesis.
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What are polypeptides made on?
Ribosomes and then transported through the cytoplasm to the Golgi body; here the polypeptide is folded into secondary, tertiary and quaternary strucutres and may be chemically modified. It's known as post-translational modification.
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How can polypeptides be chemically modified?
By combining them with non-proteins such as 1) carbohydrates to make glycoproteins 2) lipids to make lipoproteins 3) phosphate to make phospho-proteins
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Other cards in this set

Card 2

Front

What is the definition of translation?

Back

Translation is where the mRNA acts as a template for tRNA molecules, which carry amino acids to attach. It occurs on the ribosomes.

Card 3

Front

What's the process of making a polypeptide from DNA?

Back

Preview of the front of card 3

Card 4

Front

What does the DNA act as a template as in transcription?

Back

Preview of the front of card 4

Card 5

Front

Where does transcription take place in eukaryotic and prokaryotic cells?

Back

Preview of the front of card 5
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