52 WJEC Biology AS Level - Study And Revision Guide - Neil Roberts (1.5 Nucleic Acids And Their Functions) Flashcards
What are the advantages of ATP?
- Energy is released quickly from a one-step reaction involving just one enzyme (hydrolysis of glucose takes many steps).
- Energy is released in small amounts, 30.6kJ where it is needed. By contrast just one molecule of glucose contains 1880k) which couldn’t safely be released all at once.
- It is the ‘universal energy currency, i.e. it’s a common source of energy for all reactions in all living things.
What are the roles of ATP in cells?
- Used in many anabolic reactions, e.g. DNA and protein synthesis
- Active transport
- Muscle contraction
- Nerve impulse transmission.
Who proposed the molecular structure of DNA?
When did they propose it?
Whose information did they use before their proposal?
- Watson and Crick proposed the molecular structure of DNA
- They proposed it in 1953
- They used information from other scientists including Franklin and Wilkins.
What does DNA consist of?
DNA consists of two polynucleotide strands that are arranged into a double helix.
In the formation of DNA, what is the first thing that happens?
First a dinucleotide is formed when a condensation reaction occurs between two nucleotides:
The 5th carbon atom of a deoxyribose sugar is joined to the 3rd carbon atom of the deoxyribose sugar of the nucleotide above it, via the phosphate molecule.
This continues, building a single strand of DNA in the 5’-3’ direction.
In the formation of DNA, what is the second thing that happens?
DNA then forms a double-stranded molecule from two strands
One strand runs in the opposite direction to the other (anti-parallel).
Both strands are held together by hydrogen bonds that form between complementary nitrogenous bases.
In the formation of DNA, what is the third thing that happens?
The double strand then twists to form a double helix.
What is the complementary base pairing rule?
Bases between both strands pair up in a certain way which is called the complementary base pairing rule:
- Guanine forms hydrogen bonds with an adjacent cytosine molecule
- Adenine forms hydrogen bonds with an adjacent thymine molecule.
Describe the hydrogen bonds in a DNA molecule?
Hydrogen bonds are weak.
However, the sheer number of them present in a molecule of DNA over a million nucleotides long, means that collectively they are very strong.
In fact you would need to heat DNA to over 95°C to break them all!
Are the roles and advantages of ATP the same thing?
No
What is the rule for complementary base pairing?
G-C
A-T
How do you calculate the proportion of bases present in DNA?
If you know that 22% of the DNA molecule is adenine, you can work out the proportions of the other bases.
Following base pairing rule, A-T so 22% must also be thymine.
The remainder 56% must be G + C.
Therefore guanine - 28%, cytosine- 28%.
NB this only works for double-stranded molecules.
Draw a diagram of a DNA dinucleotide
