1.5 Nucleic Acids, 1.6 ATP Flashcards
What does a nucleotide consist of?
- Phosphate group
- Pentose sugar
- Nitrogen containing base
Name the pentose sugars in DNA and RNA
- DNA: deoxyribose
- RNA: ribose
State the role of DNA in living cells
- Base sequences of genes codes for functional RNA and amino acid sequence of polypeptides
- Genetic information determines inherited characteristics = influences structure and function of organisms
State the role of RNA in living cells
- mRNA: Complementary sequence to 1 gene from DNA with introns (non coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes
- rRNA: component of ribosomes (along with proteins)
- tRNA: supplies complementary amino acid to mRNA codons during translation
How do polynucleotides form?
Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)
Describe the structure of DNA
- Double helix of 2 polynucleotide strands (deoxyribose)
- H-bonds between complementary purine and pyrimidine base pairs on opposite strands: adenine+thymine, guanine+cytosine
Which bases are purine and which are pyrimidine?
A+G = 2 ring purine bases T+C+U = 1 ring pyrimidine bases
Name the complementary base pairs in DNA
- 2 H-bonds between: adenine+thymine
- 3 H-bonds between: guanine+cytosine
Name the complementary base pairs in RNA
- 2 H-bonds between adenine+uracil
- 3 H-bonds between guanine+cytosine
Relate the structure of DNA to its functions
- Sugar-phosphate backbone and many H-bonds provide stability
- Long molecule stores lots of information
- Helix is compact for storage in nucleus
- Base sequence of triplets codes for amino acids
- Double-stranded for semi-conservative replication
- Complementary base pairing for accurate replication
- Weak H-bonds break so strands separate for replication
Describe structure of mRNA
- Long ribose polynucleotide (but shorter than DNA)
- Contains uracil instead of thymine
- Single stranded and linear (no complementary base pairing)
- Codon sequence is complementary to exons of 1 gene from 1 DNA strand
Relate structure of mRNA to its function
- Breaks down quickly so no excess polypeptide forms
- Ribosome can move along strand and tRNA can bind to exposed bases
- Can be translated into specific polypeptide by ribosomes
Describe the structure of tRNA
- Single strand of about 80 nucleotides
- Folded into clover shape (some paired bases)
- Anticodon on one end, amino acid binding site on the other:
a) anticodon binds to complementary mRNA codon
b) amino acid corresponds to anticodon
Order DNA, mRNA and tRNA according to increasing length
- tRNA
- mRNA
- DNA
Why did scientists initially doubt that DNA carried the genetic code?
Chemically simple molecule with a few components
Why is DNA replication describe as ‘semi-conservative’?
- Strands from original DNA molecule act as a template
- New DNA molecule contains one old strand and one new strand
Outline the process of semi-conservative DNA replication
- DNA helicase breaks H-bonds between base pairs
- Each strand acts as a template
- Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
- H-bonds reform
Describe the Meselson-Stahl experiment
- Bacteria was grown in a medium containing heavy isotope 15N for many generations
- Some bacteria was removed to a medium containing light isotope 14N. Samples were extracted after 1 and 2 cycles of DNA replication
- Centrifugation formed a pellet. Heavier DNA (15N bases) settled closer to the bottom of the tube
Describe the structure of ATP
Nucleotide derivative of adenine with 3 phosphate groups
What does ATP hydrolase catalyse?
ATP hydrolase catalysed ATP->ADP+Pi
Explain the role of ATP in cells
- Energy released is coupled to metabolic reactions
- Phosphate group phosphorylates compounds to make them more reactive
How is ATP resynthesised in cells
- ATP synthase catalyses condensation reaction between ADP and Pi
- During photosynthesis and respiration
Explain why ATP is suitable as the ‘energy currency’ of cells
- High energy bonds between phosphate groups
- Small amounts of energy released at a time = less energy wasted as heat
- Single step hydrolysis = energy available quickly
- Readily resynthesised
