Chapter 17

Question 1

how is the information in DNA used in a cell

Answer 1

Genes are sequences of DNA which
represents a trait – blue eyes

Cannot carry out any action on its own

Gene has to be expressed in the form of protein

ONE GENE  ONE PROTEIN

Question 2

flow of information from dNA

Answer 2

Gene is expressed in two steps

DNA sequence is first converted to RNA
sequence – Transcription

2. RNA dictates the synthesis of protein
   – Translation

DNA RNA PROTEIN
(Central dogma of molecular biology)

Question 3

DNA

Answer 3

Deoxyribose
adenine
guanine
cytosine
thymine
phosphate group 
Double Stranded

Question 4

RNA

Answer 4

Sugar is ribose
nitrogenous bases
adenine
guanine
cytosine
uracil
phosphate group 
single stranded

Question 5

Messenger RNA

Answer 5

carries the code form DNA to the ribosomes

Question 6

Transfer RNA

Answer 6

carries aminoacids to the ribosomes

Question 7

ribosomal RNA

Answer 7

involved in the formation of ribosomes

Question 8

Basic units of protein

Answer 8

Amino acids ->polypeptides ->proteins

Question 9

Transcription

Answer 9

DNA –directed RNA synthesis
1. RNA polymerase is the enzyme that catalyzes
transcription
2.RNA polymerase first binds to a specific
sequence on the DNA – called promoter or start signal
3. Moves along the DNA and makes the complementary RNA strand until it reaches a stop signal
4. When it reaches the stop signal, the new RNA is released as a free transcript (Pre-mRNA)

Question 10

Modification of pre-mRNA

Answer 10

Transcription takes place in the nucleus
Pre-mRNA gets modified before leaving the nucleus
Guanine cap and adenine tails are added
DNA has a lot of protein coding regions (exons) interrupted by non-coding regions (introns)

Question 11

What is the Genetic Code

Answer 11

Sequence of 3 bases of mRNA codes for an Amino Acid

Those 3 bases are called triplet codons

Each triplet codon represents one amino acid.

Question 12

Codons

Answer 12

There are 64 different codons – this set of
codons is called the genetic code

In most species AUG codon is the
start signal called the START CODON

UAG or UAA is called the STOP CODON

Question 13

1st stage of translation

Answer 13

1. mRNA enters the ribosome
2. Only one type of tRNA can initiate protein synthesis tRNA with the anticodon UAC which is complementary to the start codonof every mRNA
3. They meet and bind at the small ribosomal subunit
4. The large subunit joins

5.The initiator tRNA, ribosomes and the mRNA
forms the initiation complex

Question 14

2nd stage of translation

Answer 14

1.A polypeptide chain is synthesized while the
mRNA passes between the two ribosomal
Subunits

2. Many tRNA molecules deliver amino acids
   to the ribosome

3.Each binds to the mRNA based on the codons
which specify them

4. Long polypeptide molecule is formed

Question 15

3rd stage of translation

Answer 15

1. mRNA stop codon enter the ribosome
2. No tRNA has a corresponding anticodon
3. Proteins called release factors bind to the
   ribosome
4. mRNA and the polypeptide chain are released from the ribosome

Question 16

Post Translational Modifications

Answer 16

Folding of the polypeptide chains
Cleaving with enzymes
Attachment of sugars, lipids or phosphate
groups

Question 17

silent mutations

Answer 17

mutations that do not change the protein structure

Question 18

nonsense mutation

Answer 18

mutations that change an amino acid codon to a stop codon

Question 19

missense mutations

Answer 19

changes the codon of one amino acid to another one