2.1.3 - Nucleotides and Nucleic Acids

a) What is the structure of a nucleotide as the monomer from which nucleic acids are made from?

Contains:

• Nitrogen Base

• Pentose Sugar

• Phosphate group

b) What bonds are formed between polynucleotides?

Phosphodiester bond through condensation by removing water

c) What is the difference between ADP and ATP, what is the reaction?

ATP- Adenosine Triphosphate

• Ribose

• Adenine

• 3 Phosphate

ADP - Adenosine Diphosphate

• 2 phosphate groups

ATP ——→ ADP + Pi

This is where ATP is hydrolysed

di) What is the structure of DNA?

• Polynucleotide - 2 Nucleotides bonded by phosphodiester bonds

• Double Helix Structure

• Hydrogen bonds between bases

• Purines are A and G

• Pyrimidines are C and T

• A to T has 2 hydrogen bonds

• G to C has 3 hydrogen bonds

• Antiparallel strands 3 to 5, 5 to 3 on the other

• Sugar phosphate backbone

What are the main difference between RNA and DNA?

DNA:

• Deoxyribose sugar

• Contains Thymine

RNA:

• Ribose sugar

• Contains Uracil instead of Thymine

dii) What is the practical investigation to purify DNA?

Precipitation:

1. Crush the sample to break down the cell wall

2. Add detergent to break down the cell membrane to allow cell contents to leave

3. Add salt to break down the hydrogen bonds between bases

4. Add the protease enzyme to remove proteins associated with DNA

5. Add ethanol to precipitate the DNA

6. Which will come out as white strands which can be collected as white strands

e) What is semi-conservative replication?

When two new molecules of DNA is produced consisting of one parent strand and one new strand.

What is the process of semi - conservative replication?

1. DNA unzips and unwinds

2. DNA helicase allows hydrogen bonds to break between the bases

3. Free nucleotides attach to the complementary bases

4. DNA polymerase joins these bases together, and forms sugar phosphate backbone

5. Forming a new molecule of DNA, with one parent strand and one new strand

f) What is the nature of genetic code?

• Non - overlapping: each base is only read once

• Degenerate: Multiple codes can code for the same amino acid

• Universal: all organisms use the same code

g) Explain transcription and translation of genes?

Transcription:

1. DNA unzips and unwinds

2. DNA helicase breaks hydrogen bonds between bases

3. Free RNA nucleotides attach to complementary bases on the template strand, whilst the other strand is the non - template strand

4. RNA polymerase catalyses this and forms a sugar phosphate backbone

5. When strand is transcribed, mRNA molecule is complete

Translation:

1. Once mRNA leaves nucleolus through the envelope (pores) it attaches to the ribosomes

2. In cytoplasm there are free nucleotides of tRNA - which is a single strand of RNA molecule

3. Each tRNA anticodon has a complementary codon from mRNA

4. Through condensation peptide bonds are formed

5. The mRNA moves along the ribosome reading the next codon

How are two chains (nucleotide) held together?

• Hydrogen bonds between bases

• Phosphodiester bonds which form sugar phosphate backbone

• Purines have to bond with pyrimidines because they are different sizes

Briefly what are the main differences between replication and transcription?

Only small part in transcription of DNA is used

RNA creates 2 new daughter strands

In transcription one new mRNA strand is formed