2 - Nucleic Acids Flashcards
What are two differences between DNA and RNA?
DNA contains a deoxyribose (pentose) sugar, RNA contains a ribose (pentose) sugar.
DNA has bases adenine, thymine, guanine and cytosine, RNA has bases adenine, uracil, guanine and cytosine.
What is the monomer of a nucleic acid?
A nucleotide.
What reaction and bond joins nucleotides?
Condensation reaction. Phosphodiester bond.
Describe the structure of a DNA molecule.
- Polymer of nucleotides
- each nucelotide made from nitogenous base, phosphate and deoxyribose
- nucleotides joined by phosphodiester bonds
- strands joined by Hydrogen bonds between complementary bases
- Hydrogen bonding between cytosine and guanine, and adenine and thymine
Explain base pairing.
As a result of complementary base pairing, adenine always bonds with thymine and guanine with cytosine.
Between G and C there are three H bonds, whereas between A and T, there are two.
Why is DNA a stable molecule?
The phosphodiester backbone protects the more chemically reactive organic bases.
A higher proportion of C-G pairings increase stability, as they contain more hydrogen bonds.
Base stacking.
Give 4 ways in which DNA is adapted to carrying genetic information.
Very stable
Strands only joined with hydrogen bonds so can easily split during DNA replication
Extremely large so carries lots of genetic information
Base pairing allows DNA to replicate and carry information as RNA
What is the function of DNA?
Passing genetic information from cell to cell and generation to generation
Outline semi-conservative replication?
DNA helicase breaks H bonds
Double helix separates and unwinds
Free nucleotides bond to template strand by complementary base pairing x 2
Nucleotides joined by DNA polymerase in condensation reaction x 2
Each new strand contains half original DNA and half new DNA
What does ATP stand for?
Adenosine triphosphate
What is the composition of ATP?
Adenine
Ribose sugar
Chain of three phosphate groups
How does ATP store energy?
The phosphate bonds are unstable and easily broken. They release large amounts of energy when broken.
What reaction converts ATP to ADP, and what enzyme catalyses this?
Hydrolysis, catalysed by ATP hydrolase
What reaction adds an inorganic phosphate to ADP to form ATP, and what catalyses this?
Condensation reaction using energy, catalysed by ATP synthase. Called phosphorylation.
How/where does phosphorylation occur?
Photosynthesis in chlorophyll-containing plant cells
Respiration in plant/animal cells
Donor molecule transferred lies inside of cell
Why is ATP used as an immediate energy source, not long term?
The phosphate bonds are very unstable. Each ATP molecule releases less energy than glucose molecule, so it is more manageable.
Where is ATP synthesised?
In the mitochondria.
What are five uses of ATP?
Metabolic processes ie making starch
Movement (muscle contraction)
Active transport (allows carrier proteins to change shape)
Secretion (needed to form lysosomes)
Activation of molecules (inorganic phosphate can be used to make other compounds more reactive)
Explain the charges and polarity of water.
Oxygen is slight negative, and the hydrogen atoms are slight positive. So the molecule is dipolar.
What are the bonds between water molecules?
Hydrogen bonds form between which stick the molecules together.
Why is water having a high specific heat capacity useful?
It acts as a buffer against sudden temperature variation. This makes both aquatic environments and organisms safer against sudden temperature changes.
Why is water having high latent heat of vaporisation useful?
Evaporation of water such as sweating is effective for cooling as much body heat energy is required.
What is cohesion?
When water molecules stick together, this allows it to be pulled through tubes such as xylem.
It also means surface water tension is high enough to support small organisms such as skaters.
Explain five properties of water that make it important for organisms. (6)
- Metabolite in hydrolysis
- Solvent so metabolic reactions can occur
- High specific heat capacity so buffers changes in temperature
- Large latent heat of vapourisation so provides a cooling effect through evaporation
- Cohesion so supports coloumns of water in plants
- Cohesion so produces surface tension supporting small organisms
Give four inorganic ions and their functions
H+, determines pH hence the functioning of enzymes
Fe2+, found in haemoglobin, transport of oxygen
Phosphate ions used in ATP
Sodium ions, transport of glucose across plasma membranes
give two features of DNA and explain how each is important in the semi-conservative replication of DNA.
Hydrogen bonds can be easily broken to allow strands to seperate
Two strands so both act as templates
describe how an ATP molecule is formed from its component molecules (3)
- Made from adenine, ribose and three phosphates
- condensation reaction
- ATP synthase
give three ways in which ATP is a suitable energy source for cells to use (3)
- releases relatively small amount of energy so small danger of thermal death
- releases energy instantaneously
- can be rapidly re-synthesised
describe how ATP is resynthesised in cells
- from ADP and phosphate
- by ATP synthase
- during respiration
give two ways in which the hydrolysis of ATP is used in cells (2)
- provides energy for other metabolic reactions ie respiration
- add phosphate to other substances and make them more reactive
Suggest how high sodium concentrations in the blood could affect blood volume. (3)
- Lowers water potential
- Water moves into blood by osmosis from tissues
- Increases blood volume
Describe the role of iron ions in cells. (1)
- Haemoglobin binds with oxygen
Describe the role of sodium irons in cells. (4)
- Co-transport of glucose
- Sodium moved out by active transport
- Creates sodium concentration gradient
- Affects water potential
Describe the role of phosphate ions in cells. (4)
- Affects water potential
- Joins nucleotides in DNA
- Used in ATP
- Phosphorylates other compounds to make them more reactive
Describe the role of phosphate ions in cells. (4)
- Affects water potential
- Joins nucleotides in DNA
- Used in ATP
- Phosphorylates other compounds to make them more reactive
Give and explain two properties of water that are important in the cytoplasm. (4)
- Reactive
- So metabolite in hydrolysis
| - Solvent
- Metabolic reactions occur faster in solution
