3.4.2 - DNA and protein synthesis

Question 1

what is protein synthesis?

Answer 1

-the production of polypeptides
-has two mains stages: transcription and translation

Question 2

what is the function of mRNA (messenger RNA) and its structure?

Answer 2

-it is made during transcription
-it carries the genetic code from the DNA to the ribosomes
-its a single polynucleotide strand
-in mRNA groups of three adjacent bases are called codons

Question 3

what is the function of tRNA (transfer RNA) and its structure?

Answer 3

-carries the amino acids that are used to make proteins to the ribosomes
-it is a single polynucleotide strand that is folded into a clover shape
-hydrogen bonds form between specific base pairs to hold the molecule in its shape
-each tRNA molecules has a specific sequence of three bases at one end called an anticodon and an amino acid binding site at the other end

Question 4

describe the process of transcription.

Answer 4

1. DNA helicase unwinds the DNA double helix by breaking the hydrogen bonds between the complementary base pairs which exposes unpaired bases on one template strand. Free RNA nucleotides from the nucleoplasm are attracted to and bind to their complementary base
2. RNA polymerase binds to the template strand at the start triplet. The enzyme moves along the DNA, catalysing the formation of phosphodiester bonds between adjacent RNA nucleotides. As the RNA polymerase pass, hydrogen bonds in the DNA reform and the strands recoil
3. When RNA polymerase reaches the stop codon, it stops and detaches from the DNA
4. In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm where translation happens.

Question 5

what is splicing and why does it happen?

Answer 5

-in eukaryotes, transcription results in the production of pre-mRNA from DNA
-pre-mRNA contains both exons and introns
-the pre-mRNA is spliced
-introns are removed and the exons are joined together, forming mRNA strands
-in prokaryotes, no splicing is necessary as there are no introns

Question 6

describe the process of translation.

Answer 6

1. The mRNA associates itself with a ribosome and the tRNA molecules carry amino acids to it. ATP provides the energy needed for the bonds between the amino acid and the tRNA molecule to form.
2. A tRNA molecules carrying an amino acid with and anticodon that is complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
3. The two amino acids are joined by a peptide bond during a condensation reaction. The first tRNA molecules moves away, leaving its amino acid behind
4. A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecules moves away. This process continues producing a chain of amino acids until there is a stop codon.
5. the polypeptide chain moves away from the ribosome.

Question 7

what is the function of transcription?

Answer 7

produce an mRNA molecule

Question 8

what is the function of translation?

Answer 8

produces a polypeptide chain

Question 9

what is a genome?

Answer 9

the complete set of genes in each cell of an organism or cell

Question 10

what is a proteome?

Answer 10

the full range of proteins that a cell or organism is able to produce

Question 11

what is the function of ATP during translation?

Answer 11

provides the energy needed for the bond between the amino acid and the tRNA molecule to form