1B Flashcards
(37 cards)
What are the monomers of DNA and RNA?
Nucleotides
What is a nucleotide made from?
A pentose sugar, A nitrogen containing organic base and a Phosphate group
Polynucleotide Structure
Many nucleotides joined together by an ester bond via a Condensation reaction, between the phosphate group of one nucleotide and the pentose sugar from another nucleotide. The chain of phosphates and sugars is known as the Sugar-phosphate backbone
DNA Structure
- Double helix, formed from two separate strands. each strand is made from polynucleotide.
- The Pentose sugar is Deoxyribose
- They are really long and tightly coiled with lot of genetic material so they are compact enough to be in a cells nuclei
What are the four possible bases and their hydrogen bond numbers?
Adenine and Thymine = 2 Hydrogen Bonds
Cytosine and Guanine = 3 Hydrogen bonds
Complementary Base pairing
Complementary Base pairing ensures there’s always the same amount of Adenine as there is Thymine, as well as Cytosine and Guanine.
How can you tell which direction the strand of DNA is running
The two ends of the polynucleotides are different, one end has a phosphate group and the other end has a hydroxyl (OH) group
What does Antiparallel mean?
The two strands run in the opposite directions.
RNA Structure
Like DNA, RNA contains nucleotides, and four bases, but the pentose sugar is Ribose and Uracil replaces Thymine. Also RNA is a single, shorter strands
Who discovered the structure of DNA?
Waston and Crick
How is DNA replicated? Semi-Conservative replication
- Enzyme DNA Helicase breaks the hydrogen bonds between the bases of the strands, so the DNA is separated into two strands.
- Each strand acts as a template strand, as free complementary bases are attracted to the free exposed nucleotides on the template strand.
- Condensation reactions join the sugar-phosphate back bone together on the new strand, and the hydrogen bonds form between the original and new bases. This is catalysed by DNA Polymerase
The Action of DNA polymerase
Each end of the DNA strand is slightly different in its structure, one end is called the 3’ (prime) and the other is called the 5’ (prime) DNA polymerase is only complementary to the 3’ end, so the DNA polymerase moves down the template in a 3’ to 5’ direction whilst the new strand is formed in a 5’ to 3’ direction. Due to DNA being antiparallel, DNA Pol. working on the template strand moves in the opposite direction to DNA Pol on the new strand
Evidence for the Semi Conservative Replication
Meselson and Stahl’s experiment - using two isotopes of nitrogen - heavy and light.
- Two samples of bacteria were grown, one in light and one in heavy nitrogen. A sample of DNA from each bacteria broths were taken and spun in the centrifuge. Heavier N settled lower than light N. The bacteria were taken out of the broth and put in light N only. After 20 mins, the first gen bacteria’s DNA was spun again and the DNA settled in the middle, showing the DNA contained one light and one heavy N - it is a hybrid
What is ATP made from?
Nucleotide base adenine, a pentose (ribose) sugar and 3 phosphate groups.
When ATP is hydrolysed (Catalysed by ATP hydrolyse and water) to ADP and iP, it only contains 2 Phosphate groups
What is the use for the inorganic phosphate released from ATP
It can make other molecules more reactive by phosphorylating them.
ADP to ATP
A condensation reaction, releasing water, synthesised by ATP Synthase
The importance of Water
- Water is a metabolite in lots of important metabolic reactions, including condensation and hydrolysis reactions
- It is a solvent, allowing many solutions to dissolve in it. Most metabolic reactions takes place in solution (Cytoplasm in Pro and Eukaryotic cells)
- Helps with temperature control due to its high Latent heat of vaporisation and high specific heat capacity
- Water molecules are very cohesive, which helps water transport in cells as well as in other organisms
Polarity of Water
because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each of the hydrogen atom is left with a slight positive charge, whilst the oxygen side has a slight negative charge. this makes the water molecule polar.
Hydrogen Bonding in Water
Weak bonds formed when a slightly positive hydrogen atom is attracted to the slightly negative charge atom (O2) in another
Water is a metabolite
Hydrolysis and Condensation reactions require water to break bonds.
Water is a good solvent
Lots of important substances are ionic, meaning they are positively or negatively charged atom/molecule. Because water is polar, each ion will be attracted to either the hydrogen atoms or the oxygen atoms, and will be surrounded by the water, dissolving the ion substance, allowing the body to take up useful substances dissolved in water, and can be transported around the body
Water and its high latent heat of vaporisation
It takes a lot more energy to evaporate water as the Hydrogen bonds must be broken
- Lots of heat is used to change it from a liquid to a gas
useful in cooling organisms down by sweating
Water can buffer/resist changes in temperatures
Hydrogen bonds give water a high specific heat capacity - the energy needed to raise the temperature of 1 gram of substance by 1 degrees. When water is heated, lot of heat energy is required to break the hydrogen bonds, therefore less heat energy is available to heat the temperature of the water - taking up a lot more heat energy
Water is very cohesive
Cohesion is the attraction between molecules of the same type. Water is cohesive as they are polar. Strong cohesion also means water has a high surface tension when it comes into contact with air
