Nucleic Acids And Protein Synthesis

Question 1

Nucleotides & polynucleotides

Answer 1

Molecule consisting of a nitrogen containing base, a pentose sugar and a phosphate group
A chain of nucleotides joined together by phosphodiester bonds

Question 2

Phosphodiester bond

Answer 2

Bond joining two nucleotides together, 2 ester bonds, one from the shared phosphate group to each of the sugars either side of it

Visual : -o-

Question 3

Complementary base pairing

Answer 3

Hydrogen bonding of A with T (or U in RNA) and of G with C in nucleic acids
AT have double H- bonds GC have triple

Question 4

Purines & Pyrimidines

Answer 4

Purines are two rings wide, A and G are purines
Pyrimidines are one ring wide, T,U and C are Pyrimidines
Purines and Pyrimidines always pair together so backbone of DNA is always 3 rings wide

Question 5

DNA Polymerase

Answer 5

Enzyme that copies DNA, runs along the separated DNA strands lining up one complementary nucleotide at a time ready to be joined by DNA Ligase

Question 6

DNA Ligase

Answer 6

Enzyme that catalyses the joining together of two nucleotides with covalent phosphodiester bonds during DNA replication

Question 7

Leading strand & Lagging strand

Answer 7

During DNA replication, the parent strand that runs in the 3’ to 5’ direction is copied to produce the leading strand.
The parent strand that runs in the 5’ to 3’ direction copied to produce lagging strand, coping opposite to direction of unwinding so it needs to keep jumping backwards resulting in short fragment called Okazaki fragments

Question 8

Semi-conservative replication

Answer 8

Method by which DNA molecule is copied to make 2 identical molecules each containing one strand from original molecule and one newly synthesized strand

Question 9

Gene

Answer 9

Length of DNA coding for a particular polypeptide or protein

Question 10

Transcription

Answer 10

Copying the genetic information in a molecule of DNA into a complementary strand of mRNA.
A single strand of the DNA is used as a template (called template/ transcribed strand ).
Enzyme responsible: RNA polymerase

Question 11

Translation

Answer 11

Stage in protein synthesis where a sequence or nucleotides in a molecule of mRNA is converted (or translated) into a corresponding sequence of amino acids in a polypeptide chain.
It takes place in ribosomes

Question 12

Codon

Answer 12

Sequence of three bases on a mRNA molecule that codes for a specific amino acid /for a stop signal

Question 13

Anticodon

Answer 13

Sequence of three unpaired bases on a tRNA molecule that binds with codon on mRNA

Question 14

Gene mutation

Answer 14

Change in base sequence in part of a DNA molecule

Question 15

Chromosome mutation

Answer 15

A random and unpredictable change in the structure or number of chromosomes in a cell

Question 16

Frame shift mutation

Answer 16

A type of gene mutation caused by insertion of deletion of one or more nucleotides, resulting in incorrect reading of genetic code due to shift in the reading frame.

Question 17

DNA/RNA general structure

Answer 17

• macromolecules known as nucleic acids
  – monomers are nucleotides
  -DNA/RNA are polynucleotides

1. Nitrogen containing bases: Adenine, Thymine, Cytosine. In RNA T is replaced by Uracil.
2. Pentose sugar: only 2 types: Ribose & Deoxyribose

3.Phosphate group : gives nucleic acids in their acidic nature.

Question 18

DNA structure

Answer 18

• 2 polynucleotide chains, coiled —–> double helix
  -chains run opposite directions, called antiparallel
• sugar phosphate backbone
  -bases bonded by H -bonding and holds chains tgt
  -complete turn every 10 base pairs

Question 19

Modification

Answer 19

-Called mRNA processing
-before leaving the nucleus the mRNA is slightly changed
- before modification is called the primary transcript

Question 20

Protein synthesis

Answer 20

-has 2 stages
1. Transcription: writing of the information of the gene in the nucleus- and mRNA copy is made
2.Translation : at ribosome mRNA is used to form a polypeptide

Question 21

Th triplet code

Answer 21

-3 bases on the DNA code for one amino acid
-the sequence is always read in one direction on one strand of DNA
-is degenerate meaning that each amino acid is coded for by more than one triplet (bc there is more than necessary only have 20 amino acids but 64 combinations)

Question 22

Transcription

Answer 22

-mRNA is built up by complementary base pairing using the DNA as a template (u instead of t)
-DNA’s triplets are converted into mRNA CODONS

Steps:

1. Helicase unwinds the DNA
   2.RNA polymerase binds to the DNA at the beginning of the gene to be copied
2. single stranded RNA copy of the template stand is made stopping when it reaches the terminator sequence.
   4.last 3 nucleotides on mRNA code for STOP
3. H bonds holding DNA and mRNA break and release mRNA