2. Nucleic Acids Flashcards
What are the 2 most important types of information-carrying molecules?
Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA)
What makes up a nucleotide?
Draw!
A pentose sugar
A phosphate group
A nitrogenous organic base (adenine, thymine, uracil, cytosine and guanine)
How do nucleotides join together?
Through condensation reactions between the pentose sugar in one nucleotide and the phosphate group in another to form a polynucleotide chain
The bonds are called phosphodiester bonds and they help form the sugar-phosphate backbone
What is the pentose sugar and bases in DNA?
The pentose sugar is deoxyribose and the bases will either be adenine, thymine, cytosine or guanine
What is the pentose sugar and what are the bases in RNA?
The pentose sugar is ribose and the bases will be adenine, uracil, cytosine and guanine
Explain the structure of DNA
DNA is made up of 2 extremely long polynucleotide chains, joined by hydrogen bonds formed between certain bases (complementary base pairing)
These 2 chains coil around each other in a double helix
Explain the structure of RNA
RNA is a single, relatively short polynucleotide chain
Describe the process of semi-conservative replication
- DNA helicase unwinds the molecule and breaks the hydrogen bonds between complementary base pairs
- these two separated strands will then act as a template for DNA replication
- free activated DNA nucleotides then complementary base pair to the newly exposed bases on the template strands
- DNA polymerase then moves along and catalyses the formation of phosphodiester bonds between adjacent nucleotides, forming the sugar-phosphate backbone and the newly synthesised polynucleotide chain
- the result is two identical DNA molecules, genetically identical to both each other and the original DNA
Why is it called semi-conservative replication?
In each daughter DNA molecule, one strand is the original DNA molecule and the other strand is newly synthesised
Which 3 facts did Meselson and Stahl bade their work on?
- All bases of DNA contain nitrogen
- nitrogen has 2 isotopes, N14 and N15 (N15 is heavier as it contains an extra neutron)
- bacteria will incorporate nitrogen from their growing medium into any new DNA they make (into the bases)
Describe work by Meselson and Stahl
- they began by growing bacteria on a medium of N15 for many generations, so that all of the DNA was made up of this isotope
- DNA was then extracted and analysed
- bacteria was then transferred to a growth medium of N14 for one generation and the DNA was extracted and analysed
- data was also analysed after 2 and 3 generations
Why is DNA said to be antiparallel
Because when nucleotides are arranged into the double helix, one strand runs in a 5’ to 3’ direction and the other runs in a 3’ to 5’ direction
Why is DNA a stable molecule?
The sugar-phosphate backbone protects bases inside of the double helix (which carries the genetic information) from external physical and chemical forces
- the base pairs and joined by hydrogen bonds which form bridges and these are strong when multiple act together
How many hydrogen bonds form between the base pairs?
3 between C and G,
2 between A and T
How is DNA adapted to its functions?
4
- very stable structure which normally passes from generation to generation without change (only rarely mutates)
- strands are joined only by hydrogen bonds which allows easy separation during replication
- extremely large and so can carry a large amount of genetic information
- genetic information is protected to some extent from external forces
What makes up a molecule of ATP
Draw!
Adenine, ribose and a chain of 3 phosphate groups
Describe the hydrolysis of ATP
ATP hydrolase (ATPase) hydrolyses ATP into ADP + Pi (inorganic phosphate)
This is because the bonds between the 3 phosphate groups are easily broken and when they do break they release a considerable amount of energy
How is ATP resynthesised?
ATP synthase catalyses the resynthesis of ATP from condensation of ADP + Pi
This reaction requires energy
Which ways can ATP be synthesised by the addition of a phosphate molecule
- in chlorophyll containing plant cells during photosynthesis (photophosphorylation)
- in plant and animal cells during respiration (oxidative phosphorylation)
- in plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation)
Why is ATP a better immediate energy source than glucose?
- hydrolysis of ATP is a single reaction that releases immediate energy rather than a long series of reactions
- each ATP molecule releases less energy than each glucose therefore is released in smaller and more manageable quantities
Explain the structure of water
A water molecule is made up of 2 hydrogen atoms and one of oxygen
Although the molecule has no overall charge, the oxygen atom has a slight negative charge and the hydrogen atom has a slight positive charge
This makes water molecules polar
What does it mean by water being extensively hydrogen bonded?
Hydrogen bonds form between the slight negative oxygen and the slight positive hydrogen molecules
These bonds act together to form important forces
How many hydrogen bonds can each water molecule form?
4
What is cohesion and why is it important?
The tendency of molecules to stick together is cohesion and it is caused by the hydrogen bonding
This allows water to move up and give support to xylem vessels through a combination of cohesion and adhesion (sticking to the xylem walls)
It also allows water droplets to form
