DNA, RNA, Water and ATP Flashcards
Why is DNA and RNA important?
They are important for carrying information
What is the function of DNA?
Holds genetic information
What is the function of RNA?
Transfers genetic information from DNA to ribosomes
What is the structure of a nucleotide?
- Pentose sugar (has 5 C atoms)
- Phosphate group
- Organic base (Cytosine, Guanine, Adenine, Uracil, Thymine)
How is the structure of a nucleotide formed?
Through a condensation reaction
What is the bond between two mononucleotides which forms?
Phosphodiester bond
What is the structure of RNA?
- Single stranded
- Short
- Pentose sugar is ribose
- Organic bases: Adenine, Guanine, Cytosine and Uracil
What is the structure of DNA?
- Double stranded (double helix)
- Long
- Strands joined by hydrogen bonds
- Organic bases: Adenine, Guanine, Cytosine and Thymine
What base pairs with Adenine? + how many bonds between the pair
Thymine (complimentary to adenine)
2 bonds
What base pairs with Guanine? + how many bonds between the pair
Cytosine (complimentary to guanine)
3 bonds
What is the structure of the double helix of DNA?
Like a ladder
Two polynucleotide chains twisted- phosphate and deoxyribose wind around each other, forming a double helix
Why is DNA a stable molecule?
- Phosphodiester backbone protects the chemically reactive bases in the double helix
- Hydrogen bonds link base pairs which forms bridges between the phosphodiester uprights, the more C+G pairings the more stable the DNA molecule (due to having 3 bonds)
- Interactive forces -> base stacking
How does the structure of DNA relate to its function?
- Stable structure -> rarely changes and most mutations are repaired
- Hydrogen bonds between two separate strands -> allow separation in DNA replication/protein synthesis
- Large -> carries lots of genetic information
- Base pairs within cylinder of deoxyribose-phosphate back bone -> genetic information is protected
- Base pairing -> DNA can replicate and transfer information as mRNA
What is required for semi-conservative DNA replication to take place?
- Four types of nucleotide present
- Both strands of the DNA molecule act as a template
- DNA polymerase (enzyme)
- Source of chemical energy
What happens in semi-conservative replication?
- Enzyme DNA helicase breaks hydrogen linking base pairs
- Double helix separates into two strands/unwinds
- Polynucleotide strands act as a template where free nucleotides bind to their complementary base pairs
- Nucleotides are joined together by DNA polymerase creating phosphodiester bonds. Unpaired bases attract complimentary nucleotides.
- All nucleotides are joined to form a complete polynucleotide chain. Two identical DNA molecules are formed, each of the new DNA molecules contains one of the original DNA strands.
What is the Watson-Crick model?
Two hypotheses:
Conservative model:
Original DNA molecule remained intact and separate DNA copy was made from new molecules of Deoxyribose, Phosphate and Organic bases -> one molecule would be made of new material, one would be made of original material
Semi-conservative model:
Original DNA molecule was split into two separate strands, these replicated their missing half. Therefore both new molecules would have half the new material and half the old one
How was the Watson-Crick model validated?
Bacteria grown in nutrient solution containing heavy nitrogen (15N) -> for several generations
Nitrogen incorporated into bacterial DNA bases
Bacteria transferred into light nitrogen solution (14N) + could grow/divide twice
DNA from different samples were extracted and spun in a centrifuge
Sample 1: DNA with bacteria grown for several generations in heavy nitrogen solution
-> DNA molecules contain 2 heavy strands
Sample 2: DNA was originally in 15N solution but was transferred for one division into 14N solution
-> DNA molecules contain 1 original heavy strand and 1 new light strand
Sample 3: DNA was originally in 15N solution but was transferred for two divisions into 14N
-> 50 % DNA molecules contain 1 original heavy and 1 new light, 50% contain both light strands
Where can DNA polymerase only bind/add nucleotides to?
Phosphate 3’ (prime) end of developing strand
5’ to 3’ direction
5’- phosphate attached (5 carbons)
3’- hydroxyl (-OH) attached (3 carbons)
What is the structure of ATP?
Adenine
Ribose
3 phosphate groups
How does ATP store energy?
Unstable bonds between phosphate groups -> low activation energy (easily broken)
When broken, lots of energy is released
What the equation for the conversion of ADP? + what type of reaction is it/ what enzyme catalyses it
ATP + Water -> ADP + Pi (inorganic phosphate) + Energy Hydrolysis reaction
ATP Hydrolase
What is an advantage of ATP?
Immediate source of energy in cells (rapidly formed so cells do not need to store a lot)
Why is ATP a better immediate energy source than glucose?
- ATP molecules release less energy than glucose therefore it is easier for cells to manage
- Hydrolysis of ATP to ADP is only one reaction but the breakdown of glucose is many reactions which takes longer to release energy
What energy-requiring processes is ATP used for?
Metabolic processes: making starch from glucose/polypeptides from amino acids
Movement: Muscle contraction-> for filaments to slide past each other and shorten the length of muscle fibre
Active transport: energy for changing the shape of plasma proteins in plasma membranes (so molecules can be moved against a concentration gradient)
Secretion: energy for forming lysosomes for secretion of cell products
Activation of molecules: inorganic phosphate formed in hydrolysis of ATP can be used to phosphorylate other compounds and make them more reactive (+ lowering activation energy)
What does dipolar mean in terms of water?
Oxygen atom has slight negative charge but Hydrogen atoms have slight positive charge (therefore both positive and negative poles)
What is the importance of hydrogen bonding to water?
Attractive forces between positive and negative poles cause water molecules to stick together
What is the specific heat capacity of water?
High specific heat capacity due to hydrogen bonding (takes a lot of energy to separate hydrogen bonds)
Acts a buffer when there are variations in temperature
What is the latent heat of vaporisation of water?
High latent heat due to hydrogen bonding (requires a lot of energy to evaporate 1 gram of water)
Provides a cooling effect and little water is lost through evaporation
What is cohesion and its relevance to water?
Cohesion-> tendency of molecules to stick together
Water has a high cohesion forces between molecules which allow it to be pulled up through a tube
Where is surface tension produced?
Water produces surface tension where it meets air
What is waters importance in metabolism?
Used in hydrolysis to break down molecules + produced in condensation reactions
Important for photosynthesis
Is the main environment for chemical reactions
What is waters importance as a solvent?
Readily dissolves other substances:
gases, wastes, inorganic ions etc
What are some other important features of water?
Evaporation - cools organisms and allows them to have a stable temperature
Not easily compressed- provides support
Transparent- aquatic plants can photosynthesise
Where do inorganic ions occur?
Inorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations
-have specific roles
