Topic 2: DNA structure

Question 1

Define gene (1 point)

Answer 1

1. A gene is a SECTION OF DNA that codes for a sequence of amino acids in a polypeptide chain (a protein).
   e. g. CFTR protein gene codes for the CFTR protein

Question 2

What is a mutation? (1 point)

Answer 2

1. A mutation is the change in the base sequence of DNA.

Question 3

Mutations can take place during ____ ________, when

the DNA is ____ ________ ___________.

Answer 3

DNA replication

not copied correctly

Question 4

DNA is a type of _______ _____.

Answer 4

nucleic acid

Question 5

DNA is found in the ______ of almost every cell.

Answer 5

nucleus

Question 6

DNA contains the ________ _____ which controls which _______ are made in the cell, which in turn controls all the inherited _____________ of an organism.

Answer 6

genetic code

proteins

characteristics

Question 7

DNA is _______ to an organism. (except identical twins)

Answer 7

unique

Question 8

Name the 2 main nucleic acids

Answer 8

1. DNA (deoxyribonucleic acid)

2. RNA (ribonucleic acid)

Question 9

DNA is a ________.

The monomers that make up DNA and RNA (nucleic acids) are called ________________.

Answer 9

polymer (polynucleotide)

mononucleotides

Question 10

Label a mononucleotide (on flashcard)

Answer 10

Phosphate

Base

Pentose sugar

Question 11

Key Summary: Describe the structure of a mononucleotide

4 points

Answer 11

1. It contains a pentose sugar (deoxyribose in DNA/ribose in RNA)
2. It contains ONE organic base ( A C G T in DNA / A C G U in RNA)
3. It contains a phosphate
4. It is made of the elements C, H, O, N and P

Question 12

Key Summary: Give 1 similarity between the structure of a DNA and RNA mononucleotide
(1 similarity)

Answer 12

SIMILARITIES:

1. Both contain a pentose sugar, organic base and phosphate

Question 13

Key Summary: Give 2 differences between the structure of a DNA and RNA mononucleotide
(2 differences)

Answer 13

DIFFERENCES:
1. A DNA mononucleotide contains deoxyribose, an RNA mononucleotide contains ribose

2. A DNA mononucleotide can contain thymine, an RNA mononucleotide can contain uracil

Question 14

Key Summary: Describe the structure of DNA

4 points

Answer 14

1. MADE OF MANY MONONUCLEOTIDES (each contains deoxyribose, one base and phosphate) JOINED BY PHOSPHODIESTER BONDS (between sugar and phosphate) IN CONDENSATION REACTIONS
2. DOUBLE HELIX - 2 STRANDS
3. COMPLEMENTARY BASE PAIRS HELD TOGETHER BY HYDROGEN BONDS (cytosine and guanine, adenine and thymine) holding the 2 strands together
4. DNA is a polynucleotide and a nucleic acid

Question 15

Label the DNA (on flashcard)

Answer 15

1. Deoxyribose sugar
2. Phosphate
3. Base
4. Nucleotide
5. Sugar-phosphate backbones

Question 16

Adenine ONLY pairs with _________.

Cytosine ONLY pairs with _________.

Why is this? (3 points)

Answer 16

Thymine

Guanine

1. A and G (purines) have a 2 ring structure
2. C and T (pyrimidines) have a 1 ring structure
3. The bases pair up so there are 3 rings forming each “rung” of the ladder, there are even widths between strands

Question 17

Two chains are held together by ____________ ________.

The strands run in opposite directions with the ___________ phosphate groups on the outside & the ___________ bases on the inside.

The ______ join in the middle of the helix (like a ladder).

The ________ and ___________ form the backbone.

Answer 17

hydrogen bonds

hydrophilic

hydrophobic

bases

sugars

phosphates

Question 18

Key Summary: Explain how base pairing is involved in the formation of the DNA double helix
(3 points)

Answer 18

1. COMPLEMENTARY base pairing - A only pairs with T, C only pairs with G
2. Hydrogen bonds form between bases (3 between C and G, 2 between A and T)
3. to HOLD the 2 DNA strands of the double helix together

Question 19

Key Summary: Explain how hydrogen bonding is involved in the formation of the DNA double helix
(2 points)

Answer 19

1. Hydrogen bonds form BETWEEN complementary base pairs (A and T, C and G)
2. to HOLD the 2 DNA strands of the double helix together

Question 20

If 36% of bases in a DNA molecule are A, what percentage of bases are G?

Answer 20

G = 14%

WORKING OUT:
If 36% of the bases are A, then 36% of the bases are T

So if you add up the percentages of these bases 36 + 36 = 72%
Then if you subtract 72% from 100% 100 – 72 = 28%

So 28% of the bases must be C and G and they are present in equal numbers
28 divided by 2 = 14
So 14% of the bases are C and 14% of the bases are G

A = 36% T = 36% G = 14% C = 14%

Question 21

Key Summary: Describe the structure of RNA

5 points

Answer 21

1. MADE OF MANY MONONUCLEOTIDES (each contains ribose pentose sugar, one organic nitrogenous base and phosphate)
2. PHOSPHODIESTER BONDS, BETWEEN SUGAR AND PHOSPHATE, join mononucleotides in condensation reactions
3. SINGLE STRANDED
4. RNA is a polynucleotide
5. RNA is a nucleic acid

Question 22

Key Summary: Compare the structures of DNA and RNA

3 similarities

Answer 22

SIMILARITIES:
1. Both polynucleotides made up of many mononucleotides joined by phosphodiester bonds

2. Both CONTAIN bases adenine, cytosine, guanine
3. Both have sugar-phosphate backbone with bases sticking out from it

Question 23

Key Summary: Contrast the structures of DNA and RNA

3 differences

Answer 23

DIFFERENCES:
1. RNA is single stranded and DNA is double stranded

2. The sugar in RNA is ribose, but the sugar in DNA is deoxyribose
3. RNA CONTAINS the base uracil, but DNA contains thymine