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what characteristic do lipids share

-they contain carbon, hydrogen and oxygen -proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates -insoluble in water -soluble in organic solvent such as alcohols and acetone

what do phospholipids contribute to

flexibility of cell membranes and transfer of lipid-soluble substances across them

lipids as source of energy

when oxidised, lipids provide more than twice energy as carbohydrates of the same mass would and release water

how lipids are waterproofing

lipids are insoluble in water so useful as water proofing. Plants and animals have waxy, lipid cuticle that store water, while mammals produce and oily secretion from sebaceous glands in the skin

lipids in insulation

-lipids help to retain body heat as they are slow conductors of heat when stored beneath body surface -also act as electrical insulators in the myelin sheath around nerve cells

lipids in protection

fat is often stored around delicate organs

structure of tryglycerides

3 fatty acids combined with glycerol

what bond is formed between fatty acid and glycerol in triglycerides

ester bond

condensation reaction of triglycerides

glycerol + 3 fatty acids

what triglycerides would be formed with 3 same fatty acids

simple triglyceride

what triglyceride would be formed with 3 different fatty acids

mixed triglyceride

what do all fatty acids have in common

carboxyl group ( -COOH) with hydrocarbon chain attached

what does saturated mean

no doble C-C bonds

what does unsaturated mean

1 or more double C-C bonds

why some unsaturated fats are oils at room temperature

double bonds cause molecule to bend and therefore it cant pack together so closely

why are triglycerides a good source of energy

they have a high ration of energy-storing carbon-hydrogen bonds to carbon atoms

why are triglycerides good storage molecules

they have low mass to energy ratio so much energy can be stored in a small volume

why storage of triglycerides does not affect storage or water potential

they are non-polar and insoluble in water

why do triglycerides provide an important source of water

they have high ration of hydrogen to oxygen atoms and release water when oxidised

how are phospholipids different to triglycerides

one fatty acid molecule is replaced by phosphate molecule

which one of fatty acid and phosphate molecule attract and repel water

-fatty acid repel water -phosphate attracts water

which two parts is phoshpolipid made out of

-hydrophilic ‘head’ (interacts with water but not with fat), phosphate -hydrophobic ‘tail’ (orients itself from water but interacts with fat) fatty acid

why are phospholipids polar

they have to ends (poles) that behave differently

how do phospholipids position themselves in water

the hydrophilic head is as close to water as possible and hydrophobic tail is as far away from the water as possible

how do phospholipids from a hydrophobic barrier between inside and outside of the cell

phospholipids are polar molecules and in aqueous environment form a bilayer within the cell surface membrane

what is a polar molecule

molecules that are charged-balanced overall but have unevenly distributed electrons

what helps phospholipid molecules to hold at the surface of the cell membrane

hydrophilic head

how are glycolipids formed

phospholipid structure allows them to combine with carbohydartes within the cell-surface membrane

Why does each type of inorganic ion have a specific role in organisms?

Its role depends on its properties (e.g. charge and ability to interact in solution), so different ions contribute differently to biological processes.

Explain why small changes in [H+]can represent a large change in pH.

pH is a logarithmic scale, so equal pH steps correspond to multiplicative (not additive) changes in [H+]

Which inorganic ion is required for the co-transport of glucose and amino acids?

Sodium ions, Na+.

Predict what would happen to glucose/amino acid uptake by co-transport if the Na+ gradient decreased.

Co-transport would be less effective because there is less driving force from Na+ moving down its gradient.

Where are inorganic ions found in organisms, and how do their concentrations typically vary?

They occur dissolved in the cytoplasm and in body fluids. Some ions are present at high concentrations, others at very low concentrations depending on role.

If [H+] decreases, what happens to pH?

pH increases.

Predict the consequence for oxygen transport if iron ions are not incorporated into haemoglobin.

Haemoglobin cannot function normally for oxygen binding/transport, so oxygen transport would be reduced.

Explain why Na+ is necessary for co-transport of glucose and amino acids.

The downhill movement of Na+ provides the driving force that enables glucose/amino acids to be carried uphill via the same transport protein.

What is the role of phosphate ions in ATP?

Phosphate ions are components of ATP, the phosphate groups are central to ATP's role in energy transfer.

If [   H +   ] increases, what happens to pH?

pH decreases.

State the role of iron ions in haemoglobin.

Fe 2 +

  forms part of haemoglobin and is required for oxygen transport (oxygen binds to the haem group containing iron).

In sodium co-transport, what happens to glucose or amino acids relative to their concentration gradient?

They are transported into cells against their concentration gradient, coupled to Na+ movement.

What is the role of phosphate ions in DNA?

Phosphate ions form part of DNA structure (the phosphate component of the backbone).

What does pH measure in terms of hydrogen ions?

pH reflects the concentration of hydrogen ions, [H+], in solution.

What inorganic ion is a component of haemoglobin?

Iron ions (Fe2+ ) are a component of haemoglobin.

In co-transport of glucose/amino acids, what is the direction of movement of Na+ relative to its concentration gradient?

Na+ moves down its concentration gradient.

Name two biological molecules that contain phosphate ions.

DNA and ATP contain phosphate ions (PO4 3−).

How is water involved in hydrolysis reactions?

Hydrolysis breaks a bond and uses a molecule of H2O as a reactant to split the molecule.

How does water’s high heat capacity buffer temperature changes in organisms?

It resists rapid temperature change, helping maintain a more stable internal or cellular temperature despite energy gains/losses.

How does cohesion support columns of water in tube-like transport cells of plants?

Because water molecules cohere, they form a continuous column that can be pulled through transport tubes without breaking easily.

Why is water a major component of cells?

Cells contain lots of water because many metabolic reactions take place in aqueous conditions and many substances dissolve and are transported in water.

What is meant by water being an important solvent for metabolic reactions?

Many solutes dissolve in water, so reactants can mix and collide in solution and reactions can occur in aqueous conditions.

How is water involved in condensation reactions?

Condensation forms a bond between two molecules and produces a molecule of H2O as a product.

What is meant by water having a relatively high heat capacity?

A lot of energy is needed to raise the temperature of a given mass of water by 1 degree

What is cohesion between water molecules?

Cohesion is the attraction between water molecules, causing them to stick together.

In metabolic reactions, what does it mean to say water is a metabolite?

Water is a reactant or a product in reactions, it is chemically changed rather than just providing a medium.

Give one reason why being a solvent makes water important for metabolism (application).

Dissolved reactants are in the same phase and can move/diffuse, increasing the chance of successful collisions for reactions.

Explain how water’s large latent heat of vaporisation provides a cooling effect with little water loss.

Evaporation removes a lot of energy per gram of water, so a small amount evaporating can remove substantial heat.

Where does surface tension occur and what causes it (in this spec context)?

It occurs where water meets air and is caused by strong cohesion between water molecules at the surface.' What is meant by water having a relatively large latent heat of vaporisation?

What is surface tension in water?

Surface tension is the tendency of the water surface to resist being broken due to strong cohesion between surface molecules

What is meant by water having a relatively large latent heat of vaporisation?

A large amount of energy is required to change water from liquid to gas without changing its temperature.

What is the typical effect of phosphorylating a compound (using Pi from ATP hydrolysis)?

It often makes the compound more reactive.

During which two processes is ATP resynthesised by ATP synthase (as specified)?

Photosynthesis and respiration.

What type of molecule is ATP, and what are its three components?

ATP is a nucleotide derivative made of ribose, adenine, and three phosphate groups.

Write the hydrolysis reaction of ATP to form ADP and inorganic phosphate.

ATP+H₂O→ADP+Pi​

What is meant by ATP hydrolysis being 'coupled' to an energy-requiring reaction?

Energy released by ATP hydrolysis is used directly to drive another reaction that requires energy, so the two reactions proceed together.

Write the resynthesis reaction for ATP from ADP and inorganic phosphate.

ADP+Pi​→ATP+H₂​O

This reaction is known as phosphorylation, where inorganic phosphate is added to ADP to reform ATP.

Describe (in words) the structure of a single ATP molecule.

Adenine is attached to ribose, which is attached to a chain of three phosphate groups.

What enzyme catalyses the hydrolysis of ATP to ADP and Pi ?

ATP hydrolase.

Define phosphorylation in the context of ATP hydrolysis.

The addition of an inorganic phosphate group (Pi) to another compound.

What enzyme catalyses the resynthesis of ATP from ADP and Pi?

ATP synthase.

What happens to the inorganic phosphate (Pi) released during ATP hydrolysis in many reactions?

It can be used to phosphorylate other compounds, often making them more reactive.

What type of reaction is ATP resynthesis from ADP and Pi?

A condensation reaction (water is produced).

What does it mean that DNA replication is semi-conservative?

Each daughter DNA molecule contains one original (parental) strand and one newly synthesised strand.

After the DNA strands separate, what attracts new nucleotides to the exposed bases?

Free DNA nucleotides are attracted to exposed bases on each template strand by complementary base pairing.

How does semi-conservative replication ensure genetic continuity between generations of cells?

Complementary base pairing produces a new strand with a base sequence dictated by the template strand, so the genetic information is copied accurately into daughter DNA molecules.

Which bonds are broken to separate the two DNA strands during replication, and where are these bonds found?

Hydrogen bonds between complementary bases are broken

these bonds are between the bases on opposite strands.

What key prediction distinguishes semi-conservative replication from conservative replication after one round of replication?

Semi-conservative predicts two DNA molecules each with one old and one new strand, conservative predicts one entirely old molecule and one entirely new molecule.

How did the Meselson–Stahl experiment provide evidence for semi-conservative DNA replication?

They showed DNA after one replication had an intermediate density (consistent with hybrid DNA), and after further replication produced both intermediate and lighter DNA, matching semi-conservative predictions.

In semi-conservative replication, what happens first to the DNA double helix?

The double helix unwinds, exposing the bases on each original strand so they can act as templates.

What is the role of DNA helicase in DNA replication?

DNA helicase unwinds the DNA double helix and breaks the hydrogen bonds between complementary base pairs to separate the strands.

How does complementary base pairing help ensure accurate copying during DNA replication?

Only nucleotides with complementary bases can form hydrogen bonds with the exposed bases, so the sequence of the template determines the new strand sequence.

Why does breaking hydrogen bonds (rather than covalent bonds) allow DNA strands to separate during replication?

Hydrogen bonds are relatively weak compared with covalent bonds in the sugar-phosphate backbone, so strands can be separated without breaking the backbone.

State the base-pairing rules that determine which nucleotides are added during DNA replication.

A pairs with T, and C pairs with G.

What enzyme joins adjacent nucleotides together during DNA replication?

DNA polymerase.

What new structure is formed when DNA polymerase joins nucleotides during replication?

A polynucleotide strand with a sugar-phosphate backbone (a new DNA strand) is formed alongside the template.

If one original DNA strand has the base sequence A T G C, what is the complementary sequence added during replication?

T A C G.

What key prediction distinguishes semi-conservative replication from dispersive replication after one round of replication?

Semi-conservative predicts whole strands are either old or new within each molecule (one of each), dispersive predicts each strand is a mixture of old and new DNA segments.

In evaluating evidence for the Watson–Crick model of DNA replication, why was Meselson–Stahl’s work particularly convincing?

Its results matched the specific predicted pattern for semi-conservative replication and ruled out conservative replication by showing hybrid DNA after one replication.

What is the role of DNA polymerase in DNA replication in terms of the reaction type?

DNA polymerase catalyses a condensation reaction that joins adjacent nucleotides to form the sugar-phosphate backbone of the new strand.

Describe the sequence of key events in semi-conservative DNA replication (5 steps).

Double helix unwinds

2) Hydrogen bonds between bases break.

3) Helicase separates strands.

4) Free nucleotides base-pair to exposed bases.

5) DNA polymerase catalyses condensation reactions joining nucleotides

What type of molecules are DNA and RNA in terms of monomers and polymers?

Both are polymers of nucleotides (polynucleotides).

What are the three components of a nucleotide?

A pentose sugar, a nitrogen-containing organic base, and a phosphate group.

What are the components of a DNA nucleotide (sugar + phosphate + bases)?

Deoxyribose, a phosphate group, and one base: adenine, cytosine, guanine, or thymine.

Compare the sugars in DNA and RNA nucleotides.

DNA contains deoxyribose

RNA contains ribose.

What reaction links two nucleotides together in a polynucleotide chain?

A condensation reaction.

What is meant by 'phosphodiester bond' in the context of DNA/RNA structure?

It is the covalent bond that links nucleotides together via the phosphate group, forming the sugar phosphate backbone.

How are the two DNA polynucleotide chains held together?

By hydrogen bonds between specific complementary base pairs.

State the two complementary base pairs in DNA.

Adenine–thymine and cytosine–guanine.

A student finds a nucleotide containing ribose. Is it from DNA or RNA, and why?

RNA, because RNA nucleotides contain ribose (DNA contains deoxyribose). A nucleotide contains uracil. Is it from DNA or RNA, and why?

What are DNA and RNA, and what are their roles in information transfer in cells?

DNA holds genetic information in all living cells. RNA transfers genetic information from DNA to ribosomes.