DNA,RNA and protein synthesis

Question 1

Nucleotides

Answer 1

Consist of 3 parts:
- A five carbon sugar molecule called a
PENTOSE SUGAR.
- A nitrogen-containing molecule called a
BASE.
- Negatively charge PHOSPHATE GROUP.

Contain the ELEMENTS:
- Carbon
-Hydrogen
- Oxygen
- Nitrogen
- Phosphorus

• Used to make both the molecules DNA and RNA.

Question 2

Polynucleotide

Answer 2

A PHOSPHODIESTER BOND is formed between:
- PHOSPHATE GROUP of nucleotide
- The HYDROXYL GROUP on carbon 2 of the pentose sugar of the other nucleotide.

Water is released ~ CONDENSATION reaction.

• The molecule we have formed between TWO nucleotides is called a DINUCLEOTIDE
• If we continue to add nucleotides by forming phosphodiester bonds we will form a polymer of nucleotides known as a POLYNUCLEOTIDE.
• Both DNA and RNA are examples of polynucleotides.
• We can BREAK the phosphodiester bond by adding back water known as a HYDROLYSIS reaction.

Question 3

DNA structure

Answer 3

• consists of two POLYNUCLEOTIDE strands which twist around each other to form a DOUBLE HELIX.
• A SUGAR-PHOSPHATE BACKBONE on the outside with the BASES in the centre.
• the two polynucleotide strands are held together by HYDROGEN BONDS , which form between the bases on opposite strands.

Question 4

COMPLEMENTARY bases

Answer 4

• The bases on one strand are complementary to the bases on the other strand.
• GUANINE on one strand always pairs with CYSTOSINE on the opposite strand.
• ADENINE always pair with THYMINE.
• This complementary base pairing is CENTRAL to how DNA functions.
• A PURINE base always pairs with a PYRAMIDINE base on the opposite strand.
• This means the DISTANCE between the sugar phosphate backbones is CONSTANT all down the DNA molecule.

Question 5

What does it mean that the two polynucleotide strands in DNA are ANTIPARALLEL?

Answer 5

• They run in OPPOSITE directions.

ONE STRAND:
- The top phosphate group will be attached to carbon 5 of the deoxyribose sugar.

• At the bottom , the hydroxyl group will be attached to carbon 3.

OTHER STRAND:
- The carbon 3 hydroxyl group is at the top.

• At the bottom we have the carbon 5 attached to the phosphate group.

Question 6

The number of HYDROGEN BONDS formed between complementary pairs and the PROPORTIONS of different nucleotides.

Answer 6

GUANINE & CYSTOSINE ~ 3
ADENINE & THYMINE ~ 2

• Because of complementary base pairing, the proportion of G & C are always the same and the proportions of A&T are always the same.
• This means we can calculate the proportions of different nucleotides.

Question 7

DNA nucleotides

Answer 7

• the pentose sugar is called DEOXYRIBOSE which has one fewer OXYGEN atoms than ribose.
• FOUR different bases ~ adenine , cytosine guanine and THYMINE.

Question 8

RNA nucleotides

Answer 8

• Have the pentose sugar RIBOSE
• FOUR different bases ~ adenine , guanine , cytosine and URACIL.

Question 9

Differences in DNA and RNA
(not already mentioned)

Answer 9

DNA:
- Found in CHROMOSOMES in the nucleus
- TWO polynucleotide strands in a double helix.

RNA:
- Found in the CYTOPLASM where it plays a key role in protein synthesis.
- ONE polynucleotide strand.