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Flashcards in Protein Synthesis Deck (25)
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Define a Gene

a gene is a length of DNA that codes for a polypeptide


What is the 'One gene, One polypeptide hypothesis'?

Genes code for polypeptides such as:
.Structural Proteins including collagen and Keratin
.Actin and myosin in muscle cells


Where is each gene located?

Each gene occupies a specific place or locus on the chromosomes


What are the 5 characteristics for a genetic code?

1. It is a triplet code (called a codon). A sequence of three NUCLEOTIDE BASES codes for an amino acid
2. Its a DEGENERATE code. All amino acids except methionine have more than one codon.
3.Some codes don't correspond to an amino acids but indicate a 'STOP' (the end of a polypeptide chain.)
4. All the codons are UNIVERSAL i.e. they are exactly the same for all living organisms
5. The code is NON_OVERLAPPING i.e. each triplet is read separately.


What are the three forms of RNA involved in protein synthesis?

1. mRNA
2. tRNA
3. rRNA


What is mRNA's role in protein synthesis?

Transcribes instructions in DNA and carries these to the ribsomes


What is tRNA's role in protein synthesis?

Carries amino acids to the ribosome


What is rRNA's role in protein synthesis?

Composes the ribosome


What are the three stages of Protein Synthesis?

1. Transcription
2. Activation
3. Translation


What is the "central dogma" of molecular genetics?



What occurs during transcription?

DNA is copied into a complementary strand of mRNA


Why does Transcription take place? (3)

1. DNA cannot leave the nucleus
2.Proteins are made in the cytoplasm
3. mRNA serves as a messenger and carries the protein building instructions to the ribosomes in the cytoplasm.


What are the 5 steps transcription?

1. The GENE in order to be transcribes UNWINDS and UNZIPS - Hydrogen bonds between complementary bases break.

2. ACTIVATED RNA nucleotides bind, with hydrogen bonds to their exposed complementary bases. This is catalysed by the enzyme DNA POLYMERASE.

3.The mRNA produced is complementary to the nucleotide base sequence on the template strand of the DNA and is therefore a copy of the coding strand.

4. The DNA rewinds

5.The mRNA is released from the DNA and passes out of the nucleus, through a pore in the nuclear envelope into the cytoplasm where it attaches to a ribosome.


What are the complementary base pairings?

U with A
G with C
A with T


What is the enzyme that catalyses the binding of nucleotides and exposed complementary base pairs?



What type of molecule does Translation start with?

mRNA molecule


What does each ribosome consist of ?

Two smaller sub units


What are the two sites on the large subunit in a ribosome?

P site (Peptide) and a A site (Amino acid)


Where does the mRNA molecule attach itself for translation?

To the small subunit of the ribosome


What are the three stages of tRNA and amino acid activation?

1. The anticodon will combine with the complementary codon on the tRNA.
2. The anticodon on the tRNA determines which amino acid it carries
3. Energy from ATP is required for the specific amino acid to attach itself to tRNA


What on the tRNA determines which amino acid it carries?

The anticodon


What are the 5 steps of translation?

1. The first ATIVATED tRNA molecule with the anticodon complementary to the first codon on mRNA arrives and attaches itself to the P SITE (PEPTIDE SITE). It carries an AMINO ACID at one end and an anticodon at the other.

2. Then a second activated tRNA with an anticodon complementary to the second codon comes and attaches to the A SITE (AMINO ACID SITE).

3. A ribosomal enzyme catalyses peptide bond formation between the two amino acids. Formation of the peptide bond requires energy, this is provided by the hydrolysis of the bond between the first tRNA and its amino acid.

4. The first tRNA molecule releases its amino acid and leaves the ribosome, leaving the P SITE vacant. The ribosome moves along the mRNA to the next codon. Another tRNA molecules brings the next amino acid into place, and a peptide bond joins the second and third amino acids, to form a polypeptide chain.

5. The process continues and the protein gets longer.


Where is the energy found that is required for the formation of a peptide bond during translation?

The hydrolysis of the bond between the first tRNA and its amino acid.


What causes the translation process to stop?

The process continues until a 'STOP' codon is reached.


Define a Polysome system?

Multiple ribosomes reading one mRNA strand at a time