2.7 DNA replication, transcription and translation

Question 1

DNA replication

Answer 1

happens during mitosis

a semi-conservative process because one strand will be from the original template and one strand will be new

Question 2

How does DNA replicate in a semi-conservative manner?

Answer 2

1. The two strands of the DNA molecule are separated by breaking they hydrogen bonds between their bases (Helicase and DNA gyrase)
2. New polymers of nucleotides are assembled on each of two single strands. A strand of DNA on which a new strand is assembled is called a “template strand”
3. Each of the new strands has the same base sequence as the old strand that was separated from the template strand
4. The two DNA molecules produced are identical to each other and to the original parent DNA molecule, because of complementary base pairing

Question 3

What is the role of helicase?

Answer 3

breaks hydrogen bonds between nitrogenous bases and splits the strands

Question 4

What is the role of DNA polymerase?

Answer 4

forms new DNA strands by ensuring hydrogen bonding between complementary base pairs and the covalent bonds between the phosphate and 3’ in the sugar

Question 5

Purpose of protein synthesis

Answer 5

to make proteins and control the rate of reactions

two processes: transcription and translation

Question 6

Transcription

Answer 6

the process by which the code contained in the DNA molecule is rewritten into a mRNA molecule

Question 7

What is the role of transcription?

Answer 7

in order to make proteins, we need to convert the information in our genes into real proteins

Question 8

What is the process of transcription?

Answer 8

1. the area of DNA that contains the gene is unwound by DNA polymerase
2. RNA nucleotides found in the nucleus are added to the template strand of the DNA by the enzyme RNA polymerase according to base-pairing rules.
3. RNA polymerase also creates covalent bonds between the nucleotides of the mRNA strand.
4. The mRNA strand contains the nitrogenous base uracil instead of thymine.
5. Once the gene has been transcribed, the mRNA strand falls off and exits the nucleus through the nuclear pore. It is then transported to the ribosomes for protein synthesis.

Question 9

What is the role of RNA polymerase in transcription?

Answer 9

controls the process of transcription
it transcribes only a gene length of DNA at a time and therefore recognises start and stop signals (codes) at the beginning and the end of the gene

Question 10

Gene

Answer 10

the sequence of DNA that is transcribed into RNA

Question 11

Antisense (template)

Answer 11

the strand that is transcribed and is complementary to the RNA sequence

Question 12

Sense (coding)

Answer 12

the strand that is not transcribed and is identical to the RNA sequence (with T instead of U)

Question 13

Translation

Answer 13

the process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids on a polypeptide chain

Question 14

What is the process of translation?

Answer 14

1. Ribosomes bind to mRNA in the cytoplasm and move along the molecule in a 5’ – 3’ direction until it reaches a start codon (AUG)
2. Anticodons on tRNA molecules align opposite appropriate codons according to complementary base pairing (e.g. AUG = UAC)
3. Each tRNA molecule carries a specific amino acid (according to the genetic code)
4. Ribosomes catalyse the formation of peptide bonds between adjacent amino acids (via condensation reactions)
5. The ribosome moves along the mRNA molecule synthesising a polypeptide chain until it reaches a stop codon
6. At this point translation ceases and the polypeptide chain is released

Question 15

What are the key components of translation?

Answer 15

Messenger RNA  (goes to…)
Ribosome  (reads sequence in …)
Codons  (recognised by …)
Anticodons  (found on …)
Transfer RNA  (which carries …)
Amino acids  (which join via …)
Peptide bonds  (to form …)
Polypeptides

Mnemonic: Mr Cat App

Question 16

Codons

Answer 16

triplets of bases that the ribosome reads the mRNA sequence in

Question 17

Genetic code

Answer 17

responsible for the construction of proteins, which may be structural components of cells or metabolism controlling enzymes

Question 18

Nucleotides

Answer 18

simplest basic unit of genetic information that are in groups of three (triplets)

Question 19

Universal

Answer 19

the genetic code is universal – almost every living organism uses the same code (there are a few rare and minor exceptions)

Question 20

What is the role of mRNA?

Answer 20

transports information from the DNA and the nucleus to the cytoplasm to make a protein; increase the rate of protein synthesis regulation

Question 21

How do codons and anticodons work together?

Answer 21

to finish off the translation part, when mRNA gives the template for amino acid, tRNA comes with anticodons (complementary codons) and binds. The location of this is as mentioned in the ribosome.