Chapter 2 - Nucleic acids Flashcards
What is the structure of a nucleotide
A nucleotide contains:
- A phosphate group (PO43-)
- A pentose sugar
- A nitrogen containing base
How are the components of a nucleotide joined
They are joined by a condensation reaction
The nitrogen containing base joins to the carbon one on the pentose sugar
The phosphate group attaches to the carbon 5 on the pentose sugar
What are nucleic acids with examples
- polymers, made up of monomers called nucleotides
- information carrying molecules
- examples of nucleic acids:
DNA - deoxyribonucleic acid
RNA - ribonucleic acid
How are nucleotides joined
They are joined by condensation reactions between the phosphate group and the carbon 3 on the pentose sugar.
They form phosphodiester bonds
This forms a polynucleotide.
DNA vs RNA
What is complementary base pairing
- Base pairs are bonded by hydrogen bonds, holding the two polynucleotide strands together.
- Adenine (A) pairs with Thymine (T) (2 H bonds)
- Guanine (G) pairs with Cytosine (C) (3 H bonds)
What is the structure of DNA
- Two sugar-phosphate backbones held together by H bonds between complementary N-containing bases
- The 2 antiparallel polynucleotide chains wrap round each other
How does the structure of DNA relate to its function
- Double stranded – both strands can act as templates
- Hydrogen bonds between complementary base pairs
easy separation of strands during replication - hold the structure together
- Complementary base pairing – allows for accurate replication
What is DNA replication
DNA replication occurs during interphase and is when the DNA forms exact replicas of itself
This is binary fission in prokaryotes and mitosis and meiosis in eukaryotic cells
What is semiconservative DNA replication and who came up with this model
- Proposed by Watson and Crick
- States that two strands in a DNA helix acts as templates to form two new helices, from free DNA nucleotides.
Process of semi conservative DNA replication
- DNA helicase breaks H bonds between complementary bases, unwinding the helix and separating the DNA strands
- Both strands act as templates
- Free DNA nucleotides line up by complementary base pairing (A-T, C-G) and H bonds form between complementary base pairs
- DNA polymerase joins adjacent DNA nucleotides (condensation reaction), forming phosphodiester bonds
- Each new DNA molecule made up of one old strand and one new
Key points: unwinding the helix, each new DNA molecule is made up of one old strand and one new
Diagram of semiconservative DNA replication
Who provided evidence for semi conservative DNA replication
Meselson and Stahl
What was the process of the experiment to prove semi-conservative DNA repliaction
- Grew bacteria in growth medium containing 15N (Generation 0)
- Centrifuged bacterial DNA
- Grew bacteria in 14N and centrifuged (Generation 1)
- Continued to grow in 14N for 2 more generations and centrifuged (Generation 2 and 3)
Diagram showing the results of Meselson and Stahl’s experiment
What is ATP and what are its uses
ATP is Adenosine Triphosphate – a nucleotide derivative
All living organisms require energy
ATP is the main source of energy used in cell processes
ATP is able to release energy rapidly
Structure of ATP
How does ATP release energy
- ATP is hydrolysed into ADP (adenosine diphosphate)
- This breaks the bond between the 2nd and 3rd phosphate group
- This is catalysed by the enzyme ATP hydrolase
diagram showing the interconversion between ATP and ADP + Pi
What are the three methods in which ATP is synthesised
- Photophosphorylation - during photosynthesis using energy from light
- Oxidative phosphorylation - during aerobic respiration
- Substrate level phosphorylation - using a phosphorus molecule from a donor molecule (the substrate)
Why is ATP a good intermediate energy source
- It releases relatively small amounts of energy so little energy is lost as heat
- It releases energy instantaneously, so energy is readily available
- It can phosphorylate other compounds, making them more reactive
- It can be rapidly re-synthesised for re-use
- It is not lost from cells
What are the uses of ATP
Metabolic reactions
Muscle contraction for movement
Active transport across membranes
Formation of lysosomes for secretion
Activation of molecules by phosphorylation – glycolysis in respiration
What is the structure and function of water
- dipolar - has positive and negative areas
- able to easily form hydrogen bonds
What are the main properties of water
Other important features of water
Ice floats - maintaining an aquatic earth habitat
Not easily compressed - provides support
Transparent - allows light through for photosynthesis
Role of the 4 inorganic ions
