3.8 Nucleic Acids

Question 1

Where were nucleic acids discovered?

Answer 1

Cell nuclei

Question 2

What are the 2 types of nucleic acids?

Answer 2

DNA and RNA

Question 3

What is the function of nucleic acids?

Answer 3

Storage and transfer of genetic material.

Synthesis of polypeptides (proteins).

Question 4

What elements do nucleic acids contain?

Answer 4

C, H, O2, N, P

Question 5

What are nucleic acids? How are they formed?

Answer 5

Large polymers formed from many nucleotides (monomers) linked in a chain

Question 6

A nucleotide is made up of three components. Name them.

Answer 6

• A pentose monosaccharide, containing 5 carbon atoms
• A phosphate group, (-PO4)2-, an inorganic molecule that’s acidic and negatively charged
• A nitrogenous base - complex organic molecule containing 1 or 2 carbon rings and a nitrogen in its structure

Question 7

How are nucleotides linked together?

Answer 7

By condensation reactions to form a polymer called a polynucleotide

Question 8

Describe the structure of polynucleotides.

Answer 8

Phosphate group @ 5th carbon of pentose sugar of one nucleotide forms a covalent bond with hydroxyl group at 3rd carbon of the pentose sugar.

Question 9

Describe the structure of what’s formed after 2 nucleotides are linked by condensation reactions?

Answer 9

Long, strong sugar-phosophate backbone, with a base attached to each sugar

Question 10

What are phosphodiester bonds broken by?

Answer 10

Hydrolysis - reverse of condensation reaction, releasing the nucleotides

Question 11

What does DNA stand for?

Answer 11

Deoxyribonucleic acid

Question 12

What type of sugar is DNA?

Answer 12

Deoxyribose - sugar w/ one less O atoms than ribose

Question 13

DNA is composed of 4 bases. What 2 groups are these bases broken into?

Answer 13

Pyrimadines

Purines

Question 14

What are pyrimadines?

Answer 14

Smaller bases, containing single carbon ring structures.

T and C

Question 15

What are purines?

Answer 15

Larger bases, containing double carbon ring structures.

A and G

Question 16

What are the 2 strands of a DNA double helix held by?

Answer 16

H bonds

Question 17

Describe specifically how 2 strands of DNA double helix are held together.

Answer 17

Each strand has a phosphate group, C5, at one end and a hydroxyl group, C3, at the other

Question 18

Why are the 2 strands of a DNA helix said to be antiparallel?

Answer 18

The strands are arranged so that they run in opposite directions

Question 19

How many H bonds hold C and G together?

Answer 19

3

Question 20

How many H bonds hold A and T together?

Answer 20

2

Question 21

Define complementary base pairing.

Answer 21

Specific H bonding between nucleic acid bases.

A/U binds to T, C binds to G

Question 22

What do the complementary base pairing rules mean in terms of how DNA bases bond?

Answer 22

Small pyrimidine bases always binds to larger purine base.

This arrangement maintains a constant distance between DNA backbones, resulting in parallel polynucleotide chains

Question 23

What else does complementary base pairing ensure?

Answer 23

DNA always has equal amounts of A and T, and C and G

Question 24

What carries an organism’s genetic code?

Answer 24

Order of sequence of bases along a DNA strand

Question 25

What does RNA play a role in?

Answer 25

Transfer of genetic information from DNA -> proteins that make up enzymes and tissues

Question 26

What does DNA store?

Answer 26

All the genetic info needed by an organism

Question 27

DNA of eukaryotes is long, compromising hundreds of genes. What is the problem with this?

Answer 27

DNA is too big to leave the nucleus to supply info directly to sites of protein synthesis

Question 28

How do eukaryotes get over the problem of DNA being too large to leave the nucleus?

Answer 28

A short section of DNA containing 1 gene is transcribed into a short mRNA molecule. Each mRNA is shorter than the chromosome of DNA.

Question 29

Describe the structure of mRNA

Answer 29

Polymer composed of many nucleotide monomers

Question 30

What's the difference between DNA and mRNA?

Answer 30

DNA sugar = deoxyribose mRNA sugar = ribose ``` DNA = T + A mRNA = U + A (Uracil replaces thymine) ```

Question 31

Is there a difference between Uracil (U) and Adenine (A)?

Answer 31

No - U still forms 2 H bonds with A

Question 32

Do nucleotides with U instead of T form in the same way?

Answer 32

Yes - by forming phosphodiester bonds through condensation reactions

Question 33

If the problem is that DNA itself is too big to leave the nucleus, how does turning it into RNA polymers help?

Answer 33

The RNA polymers are small enough to leave the nucleus - they can travel to ribosomes and trigger protein synthesis

Question 34

What happens to RNA molecules after protein synthesis?

Answer 34

RNA is degraded in the cytoplasm - phosphodiester bonds are hydrolysed and RNA nucleotides are released + reused