More Biological Molecules AS Flashcards
DNA and RNA are both types of _______ _____
nucleic acid
What is the role of DNA?
used to store genetic information
What is the role of RNA?
transfer genetic information from the RNA to the ribosomes
Ribosomes read the RNA to make polypeptides in a process called translation
Molecules of DNA and RNA are polymers of _______
nucleotides
What is a nucleotide composed of?
A pentose sugar
A nitrogen containing organic base
A phosphate group
How is a polynucleotide formed?
Nucleotides joined together via a condensation reaction between the phosphate group of one nucleotide and the sugar of another.
This formed a phosphodiester bond
The chain of phosphates and sugars is known as the sugar-phosphate backbone
Describe DNA structure
Double helix structure - formed from 2 separate strands of polynucleotides
The two polynucleotide strands are antiparallel - they run in opposite directions.
DNA molecules are really long and coiled up tightly so a lot of genetic information can fit into a small space in the cell nucleus
What is DNA nucleotide structure?
Phosphate group, pentose deoxyribose sugar and a nitrogen containing organic base
Base can change
can be either
A, T, C, G
What is complimentary base pairing?
Two DNA polynucleotide strands join together by hydrogen bonds between the bases. Each base only has one complimentary partner.
A-T
C-G
Two hydrogen bonds form between A-T
Three hydrogen bonds form between C-G
DNA vs RNA
- Sugar in RNA is ribose sugar not deoxyribose sugar
- Uracil replaces thymine as a base
- The nucleotides form a single polynucleotide strand not a double one
- RNA strands are much shorter than most DNA polynucleotides
Why does DNA replicate?
DNA copies itself before cell division so that each new cell has full amount of DNA. This method is called semiconservative replication because half of the strands in each new DNA molecule are from the original DNA molecule.
Explain DNA replication
- The enzyme DNA helicase breaks down the hydrogen bonds between bases on the two polynucleotide DNA strands. This makes the helix unwind to form 2 single strands.
- Each original strand acts as a template strand for a new strand. Complimentary base pairing means that free DNA nucleotides are attracted to their complimentary exposed bases on each original template strand
- Condensation reactions join the nucleotides of the new strand together - catalysed by the enzyme DNA polymerase. Hydrogen bonds form between the bases on the original and new strand
Describe the action of DNA polymerase
During DNA replication the active site of DNA polymerase is only complimentary to the 3’ end of the newly forming DNA strand - so the enzyme can only add nucleotides to the new strand at the 3’ end. This means that the new strand is made in a 5’ to 3’ direction and that DNA polymerase moves down the template strand in 3’ to 5’ direction.
Because the strands in the double helix are anti parallel, the DNA polymerase working on one of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand.
Explain Meselson and Stahl’s experiment
Used 2 isotopes of nitrogen
- Two samples of bacteria were grown, one in a nutrient broth containing light nitrogen and one containing heavy nitrogen. As the bacteria grew and reproduced, they took up the broth to help make nucleotides so nitrogen is becoming a part of the DNA
- A sample of DNA was taken from each bacteria. The DNA from heavy nitrogen broth settled lower in the centrifuge tube than the lighter nitrogen broth bacteria
- Then the bacteria grown in heavy nitrogen broth was taken out and put in a broth containing only light nitrogen. The bacteria were left for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge
- If replication was conservative the original heavy DNA would settle at the bottom and new light DNA would settle at the top
- If replication was semi-conservative, the new bacterial DNA molecules would contain one heavy strand and one light strand. So the DNA would settle between where light and heavy would have settled.
- The DNA settled in the middle showing the replication is semi conservative
Why is energy important?
Plants need energy for things like active transport, DNA replication, cell division and protein synthesis
Animals need energy for things like active transport(e.g. absorb glucose from the ileum epithelium into the bloodstream), DNA replication, cell division and protein synthesis
Describe the structure of ATP
Nucleotide base adenine combined with a ribose sugar and three phosphate groups
Once made, ATP diffuses to the part of the cell that needs energy
The energy in ATP is stored in high energy bonds between the phosphate groups
What happens to ATP when energy is needed in a cell?
ATP is broken down into ADP + Pi by a hydrolysis reaction
A phosphate bond is broken and energy is released. The reaction is catalysed by the enzyme ATP hydrolase
ATP hydrolysis can be ‘_______” to other energy requiring reactions in a cell- this means that energy released can be used directly to make the _______ reaction happen, rather than being lost as heat
coupled
The release inorganic phosphate can also be put to use - it can be added to another compound - this is known as ___________ , this often makes the compound more reactive
phosphorylation
How is ATP resynthesised?
Condensation reaction between ADP and Pi
Happens during respiration and photosynthesis and is catalysed by the enzyme ATP synthase
What is the importance of water?
- Water is a metabolite in loads of important metabolic reactions including condensation and hydrolysis
- Water is a solvent - most metabolic reactions so water is essential
- Water helps with temperature control because it has a high latent heat of vaporisation and high SHC
- Water molecules are very cohesive which helps water transport in plants as well as transport in other organisms
Explain the structure of water
Water is polar as has slight - and slight + on different sides
Hydrogen bonds form between water molecules because the slightly negative charged oxygen atoms attract the slight positive hydrogen atoms.
Explain how water is an important metabolite
Many metabolic reactions involve condensation or hydrolysis for example amino acids joined to make polypeptides by condensation, energy from ATP is released through hydrolysis
Explain how water is a good solvent
Because water is polar, the slightly positively charged end of a water molecule will be attracted to the negative ion, and the slightly negatively charged end of a water molecule will be attracted to the slightly positively charged molecule. This means that ions will get surrounded in water molecules so there will be dissolved.
This means that living organisms can take up useful substances dissolved in water and these dissolved substances can be transported around the body.
Explain how water has a high latent heat of vaporisation
Water evaporates when the hydrogen bonds are broken. It takes a lot of energy to do this so a lot of energy is used up when water evaporates. This means water has a high latent heat of vaporisation.
This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water.
Explain how water can buffer (resist) changes in temperature
Hydrogen bonds give water a high specific heat capacity. When the water is heated, a lot of the heat energy is used to break the hydrogen bonds between water molecules so there is less heat energy to increase the temperature of the water.
This is useful for living organisms because it means that water doesn’t experience rapid temperature water changes - making water a good habitat as the organisms remain at a fairly stable temperature.
Explain how water is very cohesive
Cohesion is the attraction between molecules of the same type. Water molecules are very cohesive because they are polar. Strong cohesion helps water flow to help substances to be transported. Strong cohesion also means that water has a high surface tension when it comes into contact with air.
An ion with a positive charge is called a ______
cation
An ion with a negative charge is called an ______
anion
What are inorganic ions and what are their uses?
Inorganic ion = doesn’t contain carbon (few exception). There are inorganic ions in solution in the cytoplasm of cells and in the body fluids in organisms.
Iron ions in haemoglobin
Fe2+ binds to the oxygen in haemoglobin. When oxygen is bound, Fe2+ become Fe3+ until oxygen is released
Hydrogen ions
More H+ present the lower the pH so more acidic
Sodium ions
A molecule of glucose or an amino acid can be transported into a cell alongside sodium ions = co-transport
Phosphate ions
When a phosphate ion is attached to another molecule, it is known as a phosphate group. It is the bonds between phosphate groups that store energy in ATP. The phosphate groups in DNA and RNA allow nucleotides to join up to form the polynucleotides.
