1.5 Nucleotides

WJEC A-Level Biology

What 3 components make up a nucleotide?

What 3 components make up a nucleotide?

• A phosphate group

• A pentose sugar

• A nitrogenous organic base

What reaction forms a nucleotide?

Condensation reaction

What is the full name for ATP?

Adenosine Triphosphate

What are the 3 components of ATP?

• Ribose - sugar

• Adenine - base

• 3 phosphate group

What is the role of ATP?

release energy where and when it is needed in appropriate amounts

What are some examples of things that use ATP?

• active transport

• muscle movement

• nerve transmission

Why is ATP a ‘universal energy source’?

• release energy where and when it is needed in appropriate amounts

• only needs one enzyme

What is the ATP cycle?

What is the structure of DNA?

• Two anti-parallel strands of polynucleotides

• Double helix

• Sugar and phosphate backbone

• Complimentary bases joined by hydrogen bonds

What sugar is in DNA?

Deoxyribose

What bases pair up in DNA?

• Adenine + Thymine

• Guanine + Cytosine

What is a purine and examples?

• 2 nitrogenous rings

• Adenine

• Guanine

What is a pyrimidine and examples?

• 1 nitrogenous ring

• Thymine

• Cytosine

What is the role of DNA?

• self-replicate

• carry genetic information for protein synthesis

Stages of DNA replication

1. DNA helix unwinds and DNA Helicase breaks the hydrogen bonds

2. Free nucleotides are attracted to their complimentary bases

3. DNA Polymerase catalyses the reaction

4. DNA re-winds with one ‘old’ and one ‘new’ strand

Explain the Meselson and Stahl experiment

1. E-Coli grown with only Nitrogen-15 available (heavier)

2. E-Coli transferred to dish with only Nitrogen-14 available (lighter)

3. Centrifugation

4. After first generation - band forms in middle proving the DNA has one ‘new’ strand (14N) and one ‘old’ strand (15N)

5. After second generation - exposed to Nitrogen-14 again, one band was lighter so contained 2 ‘new’ strands and one stayed in the middle again

How did the Meselson and Stahl experiment prove the semi-conservative theory of DNA replication?

As after each generation, DNA had one ‘new’ and one ‘old’ strand

What is the structure of RNA?

• single stranded polynucleotide

• single helix

What sugar is in RNA?

Ribose

What are the base pairs in RNA?

• Adenine + Uracil

• Guanine + Cytosine

Messenger RNA (mRNA)

• single strand

• made in nucleus

• bases run along it’s length

Transfer RNA (tRNA)

• found in cytoplasm

• clover leaf shape

• CCA code at top where amino acid attatches

• Bottom has anticodon - complimentary to codon on mRNA

Ribosome (rRNA)

• found in cytoplasm

• made of Ribosomal RNA and protein

• holds mRNA and tRNA together in protein synthesis