1
Q
What are the three components of ATP?
A
- Adenosine triphosphate is a nucleotide and is a phosphorylated macromolecule
- Adenine - a nitrogen-containing organic base
- ribose - a sugar molecule with a 5-carbon ring structure (pentose sugar) that acts as the backbone to which the other parts are attached
- phosphates - a chain of three phosphate groups
2
Q
How does ATP store energy?
A
- Stores energy in the bonds between the phosphate groups
- The phosphate groups are unstable and have a low activation energy, which means they are easily broken.
3
Q
How is energy released in ATP? (equation and details)
A
- ATP + H2O -> ADP + P(i) + E
- It is a hydrolysis reaction with the presence of the enzyme ATP hydrolase
4
Q
How is ATP synthesised ?
A
- It is a reversible reaction so ATP can be reformed through a condensation reaction with the presence of the enzyme ATP synthase. The product is ATP.
5
Q
What are the three ways the synthesis of ATP can happen?
A
- in chlorophyll-containing plant cells during photosynthesis ( photophosphorylation)
- in plant and animal cells during resperation (oxidation phosphorylation)
- In plant and animal cells when phosphate groups are transferred from donor molecules to ADP ( substrate-level phosphorylation)
6
Q
Why is ATP a good immediate energy source?
A
- Can be used to phosphorylate other compounds making them more reactive
- Bonds between phosphate groups in ATP are unstable and have a low activation energy therefore can be easily broken, releasing lots of energy in the process.
- Each ATP molecule releases less energy than one glucose molecules - these smaller amounts of energy are more manageable for all reactions.
- The energy is released in a single reaction and so is very rapid. Breaking down glucose requires several steps and so is slower.
- It can be recycled
- It is a small molecule so can be moved around cells easily.
7
Q
What processes does ATP provide energy for?
A
- metabolic processes -> ATP provides energy needed to build up macromolecules from their basic units.
- movement -> ATP provides energy for muscle contractions. Provides energy for the filaments of muscle to slide past one another and therefore shorten the overall length of a muscle fibre.
- active transport -> ATP provides the energy to change the shape of carrier proteins in plasma membranes. This allows molecules or ions to be moved against a concentration gradient.
- secretion -> ATP is needed to form the lysosomes necessary for the secretion of cell products.
- activation of molecules -> The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds in order to make them more reactive, thus lowering the activation energy in enzyme-catalysed reactions.
8
Q
What are nucleotides made up of?
A
- a pentose sugar
- a phosphate group
- a nitrogen-containing organic base (cytosine, thymine, uracil, adenine and guanine)
8
Q
How do mononucleotides form?
A
- The pentose sugar, phosphate group and organic base are joined, as a result of condensation reactions, to form a single nucelotide.
9
Q
How are two mononucleotides joined?
A
- Condensation reaction between the deoxyribose sugar of one mononucleotide and the phosphate group of another.
- The bond formed between them is called a phosphodiester bond.
- The new structure is called dinucleotide.
- The continued linking of the mononucleotides will form a long chain known as a polynucleotide.
10
Q
Structure of RNA
A
- Polymer made of nucleotides
- It is a single short chain
- Its pentose sugar is always ribose.
- It’s bases are adenine, guanine, cytosine and uracil.
11
Q
Quick history of the structure of DNA
A
- 1953, James Watson and Francis Crick worked out the structure of DNA, following pioneering work by Rosalind Franklin on the X-ray diffraction patterns of DNA.
12
Q
Structure of DNA
A
- Pentose sugar is deoxyribose
- The bases are adenine, thymine, guanine and cytosine
- It is made up of two strands and is extremely long.
- The strands are held together by hydrogen bonding between certain bases.
- It is a double helix structure
13
Q
Why is DNA a stable molecule?
A
- The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
- Hydrogen bonds link the organic base pairs forming bridges between the phosphodiester uprights. As there are three hydrogen bonds between cytosine and guanine, the higher the proportion of C - G pairings, the more stable the DNA molecule.
14
Q
How is DNA adapted for its function?
A
- It is very stable which normally passes from generation to generation without significant change. Most mutations are repaired, so persistent mutations are rare.
- Its two separate strands are joined only with hydrogen bonds, which allows them to separate during DNA replication and protein synthesis.
- It is an extremely large molecule and therefore carries an immense amount of genetic information.
- By having the base pairs within the helical cylinder of the deoxyribose-phosphate backbone, the genetic information is to some extent protected
- Base pairing leads to DNA being able to replicate and to transfer information as mRNA
15
Q
What are the two main stages of cell division?
A
- NUCLEAR DIVISION is the process by which the nucleus divides. There are two types of nuclear division, mitosis and meiosis.
- CYTOKINESIS follows nuclear division and is the process by which the whole cell divides.
16
Q
What is the model for DNA replication called?
A
- Semi-conservative replication
17
Q
Describe how DNA replicates
A
- The double helix unwinds
- DNA helicase breaks the hydrogen bonds linking the pairs and the DNA unwinds
- Each exposed polynucleotide strand then acts as a template to which complementary free nucleotides are attracted to and bind by specific base pairing.
- Nucleotides are joined in a condensation reaction by the enzyme DNA polymerase to form the ‘missing’ strand on each of the two original strands.
- Each of the new DNA molecules contains one of the original DNA strands.
18
Q
How does DNA and RNA code for a polypeptide?
A
- Because the base sequence in triplets determine the order of amino acid and hence the structure of the primary structure.
AS-Level Biology
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