L.3 Biopolymers: DNA, RNA, Proteins

Question 1

L.O.

Answer 1

• Identify the conventions of direction/ends of protein and nucleic acids.
• Describe the repeating units (backbones and sidechains or bases) in proteins and nucleic acids
• Identify the main chemical components of nucleic acids and proteins/peptides.
• Describe how the physical and chemical properties of proteins and nucleic acids can be exploited in experimental situations.
• Appreciate that DNA is the source of genetic information
• Describe the base pairing between nucleobases and appreciate that C/G base pairing is stronger than A/T(U) base pairing in nucleic acids
• Describe the double-helical structure of DNA
• Distinguish DNA from RNA in terms of structure and stability

Question 2

Biopolymers

Answer 2

• Info containing
• Have a defined beggining and end
• Synthesized in 1 direction only, increasing the backbone

Question 3

Nucleic acids

Answer 3

5’ to 3’

Question 4

Proteins

Answer 4

N’ to C’ (N terminus to C terminus)
- N from Nitrogen in Amino terminus, C from carbon in Carboxy terminus

Question 5

Residues (terminology)

Answer 5

Refers to a single amino acid on a protein chain
- Eg, ‘T’ in ‘ATYHWLLLGAD’

Question 6

Nucleic acid polymers

Answer 6

DNA / RNA
- Build from phosphate, sugar, base/ nucleobase
- 5’ to 3’

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Question 7

DNA Vs RNA bases

Answer 7

DNA:
- Adenine = T
- Guanine = C
- Cytosine = G
- Thymine = A

RNA:
- Adenine = U
- Guanine = C
- Cytosine = G
- Uracil = T

Apple = Tree
Car = Garage

Question 8

Properties of the common backbone

Answer 8

• Common, no matter the base
• -ve charge (Phosphate)
• Hydrophilic (Sugars & phosphate)
• Makes it well suited to electrophoresis
• Ethanol precipitation

Question 9

Proteins

Answer 9

• Amino acid = monomer
• Common peptide backbone ( N-C-C)
• 20 different amino acid side chains

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Question 10

Peptide bond formation

Answer 10

• 2 amino acids combine via condensation reactions to form a dipeptide
• Uses lots of energy

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Question 11

Peptide bond resonance

Answer 11

• e- are rearranged upon creation of peptide bonds (can be shared to create equilibrium and fullfiull octet rule)
• Leaves an overall partiual charege on LHS & RHS
• Makes the backbone polar, encouraging hydrogen bonding

Question 12

Polypeptide backbone

Answer 12

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Question 13

Amino acid side chains

Answer 13

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Question 14

Aromatic protein sidechains and nucleobases

Answer 14

• There are 3 aromatic amino acid sidechains

Aromatic sidechains absorb light at:
- Protein ~280nm
- Bases ~260nm

• Aromatic rings are flat/ planar
• Absorbtion shows a molecule may be pure / contains DNA/ RNA

Question 15

Base Pairing

Answer 15

• 2 strands (each helix) are bonded together at complementary bases by hydrogen bonds
• C & G bonds are stronger
• A & T = 2x H bonds
• C & G = 3x H bonds

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Question 16

DNA Double Helix: B-DNA

Answer 16

• Strands run in opposite directions
• Bases are aromatic and flat, stack on eachother
• -ve charged phosphates repel eachother
• B-DNA is A symetric with major & minor grooves

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Question 17

RNA

Answer 17

• Does NOT form B-type structure
• The extra OH group on the sugar stops it forming long B-DNA helices, making RNA much more sesceptible to degradation

Question 18

DNA Vs RNA

Answer 18

• Bases are very stable generally, except fot sponaneous deamination of C to U. (loses NH3 group from cytosine, turning into uracil)
• If deamination occurs in DNA, it is converted back into Cytosine quickly.
• If occurs in RNA, does not repair