Nucleotides and Nucleic Acids

Question 1

Who determined the structure of DNA and how?

Answer 1

Rosalind Franklin, James Watson and Francis Crick. Using X-Ray crystallography to find the structure

Question 2

What are the monomers of DNA and RNA

Answer 2

DNA - deoxyribose sugar, phosphate and a base
RNA - ribose sugar, phosphate and a base

Question 3

How are polynucleotides/nucleic acids formed

Answer 3

Condensation reaction forming a phosphodiester bond between the phosphate group of one nucleotide and C3 of another nucleotide

Question 4

What are the two types of nitrogenous bases and what bases do they include

Answer 4

Purine - Adenine, Guanine
Pyrimidine - Thymine, Cytosine, Uracil

Question 5

How are two strands held together in DNA

Answer 5

Hydrogen bonding between a pyrimidine and a purine in DNA

Question 6

What is the Complementary base pair rule

Answer 6

A purine always bods with a pyrimidine
A-T - two H bonds
G-C - three H bonds

Question 7

What does anti-parallel mean

Answer 7

The two DNA strands run in opposite directions

Question 8

What is DNA structure like

Answer 8

Chain twisted every 10 nucleotides to form a double helix structure
Anti-parallel

Question 9

What are the three models of DNA replication

Answer 9

Semi-conservative
Conservative
Dispersive

Question 10

Describe Semi-Conservative replication

Answer 10

Takes place in the nucleus
Double Helix is untwisted by gyrase
H bonds broken by helicase
Each strand acts as a template
Free DNA nucleotides in nucleus align with exposed nucleotides
Complimentary base pairing occurs
H bonds form
Phosphodiester bonds form between free nucleotides using polymerase

Question 11

Where does Semi conservative replication take place in Bacteria, Chloroplasts and mitochondria

Answer 11

Bacteria - nucleoid + plasmid
Chloroplasts and mitochondria - plasmid

Question 12

What is the Meselson-Stahl experiment

Answer 12

Proved semi-conservative replication
Grew E.coli in N15
- when put through centrifuge, all E.coli moved down in Gen 0
Then placed in N14
- Hybrid strand formed in Gen 1
Gen 2 - 50% hybrid, 50% N14

Question 13

What is a gene

Answer 13

A sequence of DNA that codes for a protein

Question 14

What is transcription

Answer 14

transcribing a gene into a strand of mRNA

Question 15

What is translation

Answer 15

Translating a mRNA strand into a polypeptide chain on a ribosome

Question 16

What are the differences between RNA and DNA

Answer 16

RNA has ribose instead of deoxyribose
RNA has uracil instead of Thymine
RNA is a single strand polynucleotide

Question 17

How many forms of RNA exist

Answer 17

3 - messenger RNA, ribosomal RNA, transfer RNA

Question 18

What is messenger RNA

Answer 18

Copy of template strand, has codons
Involved in transcription and translation
Made in nucleolus and moves to ribosome as a template for protein synthesis

Question 19

What is a codon

Answer 19

3 adjacent nucleotides that code for an amino acid

Question 20

what is ribosomal RNA

Answer 20

complex molecule that accounts for half the mass of a ribosome
takes part in translation

Question 21

What is transfer RNA

Answer 21

Small single strand (80 nucleotides)
Clover leaf shape
has binding site for specific amino acids
has unpaired triplet of bases called an anticodon
carries an amino acid to ribosome where they bond to form a polypeptide

Question 22

What is the process of Transcription

Answer 22

Gene unwinds and helicase breaks H bonds
Only one DNA strand is used as a template strand
Free RNA nucleotides bind to complimentary base on template strand
RNA polymerase catalyses formation of phosphodiester bonds between RNA nucleotides
mRNA is complimentary to template strand and a copy of coding strand
mRNA released from DNA and goes through a nuclear pore to a ribosome

Question 23

What is the process of Translation

Answer 23

mRNA binds to ribosome
tRNA attaches and its anticodon binds to the 1st codon of mRNA
tRNA is carrying a specific amino acid
2nd tRNA binds to 2nd exposed codon via its anticodon
peptide bond forms between 2 amino acid
ribosome moves along mRNA
1st tRNA leaves, and a 3rd tRNA brings another amino acids
Polypeptide chain grows until a stop codon is reached

Question 24

What are some features of the DNA code

Answer 24

Order of bases = order of amino acids
read in triplets
each triplet codes for one amino acid
has stop codes

Question 25

Features of the genetic code

Answer 25

universal, degenerate, non-overlapping

Question 26

What are ATP and ADP

Answer 26

Phosphorylated nucleotides produced during respiration

Question 27

What does hydrolysis of ATP do

Answer 27

Creates ADP and Pi, releases energy

Question 28

Describe DNA Extraction

Answer 28

Mash up banana
Add detergent and salt
- detergent is added to increase permeability of membrane
- salt binds with DNA, forcing it to clump together
Heat sample for 15 mins at 60• to denature the enzymes responsible for breaking DNA
Cool on ice for 5 mins
Filter mixture into test tube
Add protease enzyme to filtered mixture
Dribble cold ethanol down the side so it forms a layer

Question 29

What does DNA lygase do

Answer 29

it rejoins the DNA strands during replication