1.5- Nucleic Acid

Question 1

1. What is the name of the monomer that forms nucleic acids.

Answer 1

Nucleotide

Question 2

Draw nucleotide

Answer 2

0

Question 3

1. Name the reaction and the bond formed between to monomers

Answer 3

1. Condensation reaction forms phosphodiester bonds between nucleotides.

Question 4

Name the bonds present between the DNA nucleotides?

Answer 4

1. Phosphodiester bonds

Question 5

Name the bonds present between the complimentary base pair

Answer 5

1. Hydrogen bonds

Question 6

Sugar-phosphate backbone
Helix/Coiling
Large Molecule
Sequence of bases
Double helix with many hydrogen bonds
Double stranded/Two strands
Double helix
Hydrogen bonds between the bases are weak and easily broken 
Complementary base pairings

Answer 6

Sugar-phosphate backbone Gives strength
Helix/Coiling Gives it a compact shape
Large Molecule Stores lots of information
Sequence of bases Allows information to be stored/codes for amino acids
Double helix with many hydrogen bonds Makes the DNA molecule stable
Double stranded/Two strands BOTH strands can act as templates during semi-conservative replication
Double helix Prevents the code being corrupted
Hydrogen bonds between the bases are weak and easily broken Allows the strands to be separated for replication and also for protein synthesis
Complementary base pairings Allows accurate replication

Question 7

What is meant by specific base pairing?

Answer 7

• Each base is complementary to one other base – this is the one that it binds to.
• Guanine and cytosine are complementary to each other and therefore ONLY bind to each other
• Adenine and thymine are complementary to each other and therefore ONLY bind to each other

Question 8

What do we mean by ‘the strands are anti-parallel’?

Answer 8

The strands go in opposite directions. One strand goes in the 5’to 3’ direction the other goes in the 3’ to 5’ direction

Question 9

Describe the differences between DNA and RNA (5 marks)

Answer 9

• DNA has A,T,C,G bases whereas RNA has A,U,C,G
• DNA has a deoxyribose sugar whereas RNA has a ribose sugar
• DNA is double stranded wheras RNA is single stranded
• DNA is a large polymer RNA is a short polymer
• DNA holds genetic information in the nucleus whereas RNA transports genetic information to the ribosome

Question 10

Describe the differences between DNA in prokaryotes and Eukaryotes

Answer 10

• DNA in eukaryotes is coiled up around proteins called HISTONES whereas the DNA in prokaryotes is not
• DNA in eukaryotes is linear whereas DNA in prokaryotes is circular
• DNA in eukaryotes is found in a nucleus, whereas DNA in prokaryotes is in the cytoplasm

Question 11

A gene is a section of DNA located at a particular site on a DNA molecule, called it

Answer 11

locus

Question 12

es are a specific sequence of bases which can code fo

Answer 12

• es are a specific sequence of bases which can code for the amino acid sequence of a polypeptide or functional RNA (E.G. ribosomal RNA and tRNA)

Question 13

• 3 bases on DNA are called a TRIPLET CODE  3 bases CODE for 1 amino acid. Each triplet codes for a SPECIFIC amino acid.

Answer 13

• 3 bases on DNA are called a TRIPLET CODE  3 bases CODE for 1 amino acid. Each triplet codes for a SPECIFIC amino acid.

Question 14

What is the link between DNA bases, amino acids and a protein?

Answer 14

• What is the link between DNA bases, amino acids and a protein? A sequence of bases codes for a sequence amino acids to form a polypeptide chain which can fold into a protein.

Question 15

Introns

Answer 15

• - non-coding DNA within a gene

Question 16

Universal

Answer 16

• = each triplet codes for the same amino acids in all organisms

Question 17

Non-overlapping

Answer 17

• each base is only used in one triplet code

Question 18

Degenerate

Answer 18

• Some amino acids are coded for by more than 1 triplet code/codon

Question 19

Genome is

Answer 19

• he complete set of genes in a cell

Question 20

Proteome

Answer 20

• s the full range of different proteins that a cell is able to produce at a given time

Question 21

Why might changing the base sequence of a gene lead to a non-functional protein being formed?

Answer 21

Different base sequence  codes for a different sequence of amino acids (different primary structure)  Different hydrogen, ionic and disulphide bonding between R-groups  different tertiary structure  protein is a different shape so no longer functions

Question 22

Describe the process of DNA replication

Answer 22

o DNA helicase causes H-bonds to break and strands to separate
o Both strands act as templates
o Free DNA nucleotides attach to each strand by
o complementary base pairing (A binds with T and G binds with C)
o H-bonds form between the complementary base pairs
o DNA polymerase joins nucleotides on the new strand together (causes the covalent bond between the sugar and phosphate to form)

Question 23

Why is DNA replication described as being ‘semi-conservative’

Answer 23

Because each new double helix is made of one old strand and one new strand of DNA

Question 24

• Meselson and Stahl grew bacteria on a medium containing N15¬.. Why is this Nitrogen different to ‘normal’ nitrogen and why was it used? (What was the Nitrogen incorporated into in the bacteria?)

Answer 24

It is an isotope of nitrogen so it is more dense. This nitrogen was incorporated into the nitrogenous bases in the DNA

Question 25

• They then moved the bacteria to a medium containing N14. When they took a sample of DNA from these bacteria after they had grown on the new medium for 1 generation, what did they notice about the density of the DNA compared with DNA from the original bacteria? Explain your answer.

Answer 25

The DNA from the bacteria which had grown on N14 for one generation was less dense than the DNA from bacteria that had only grown on N15.

Question 26

• After a second generation on the N14 medium they found that they had DNA double helices of 2 different densities. Explain their finding:

Answer 26

Some of the DNA molecules were made of one strand of DNA that contained N15 and one strand of DNA that contained N14. Some of the DNA molecules were made of DNA in which both strands contained N14. These DNA molecules (with only N14 ) were less dense