Module 2

Question 1

Give 4 properties of water and their benefits

Answer 1

High specific heat capacity - makes it a good habitat
High latent heat of evaporation - helps cool the surface of skin
Polar - makes it cohesive allowing it to transport substances like in transpiration, also good solvent
Less dense when solid - ice can float and form an insulating layer for fish in cold areas.

Question 2

Draw alpha and beta glucose molecules.

Answer 2

The carbon to the right of the oxygen has OH on bottom for alpha glucose. It’s at the top for beta glucose.

Question 3

What is sucrose, lactose, fructose, amylose, galactose and maltose made of?

Answer 3

Sucrose is made from alpha glucose and fructose.
Lactose is made from alpha glucose/beta glucose and galactose.
Maltose is made from two alpha glucose molecules
Amylose is made from many alpha glucose molecules.
Fructose and galactose are both monomer structures.

Question 4

Describe starch.

Answer 4

Plants store glucose as starch. Starch is a mixture of two polysaccharides: amylose and amylopectin. Starch is insoluble in water.

Amylose is a long unbranched chain of alpha glucose it has a coiled structure which makes it compact and good for storage because you can fit it in a small space.

Amylopectin is a long branched chain of alpha glucose . Side branches allow the enzymes to reach the glycosidic bonds easily so the molecule can be broken more easily. The glucose can be released quickly.

Question 5

Describe glycogen

Answer 5

Animals store excess glucose as glycogen, it’s a polysaccharide of alpha glucose. It has a lot of side branches so that stored glucose can be released quickly. It’s compact so it’s good for storage.

Question 6

Describe cellulose

Answer 6

It’s made of long, unbranched chains of beta glucose. It’s made of straight chains which are linked together by hydrogen bonds to form microfibrils. This is strong and is good for structural support.

Question 7

Describe triglycerides

Answer 7

Made from one glycerol and 3 fatty acids. The tails are hydrophobic. They contain ester bonds formed in an esterification reaction where condensation reactions form the ester bonds. Fatty acids can be unsaturated or saturated. Heads are hydrophilic.

Question 8

Describe proteins

Answer 8

Primary structure - sequence of amino acids
Secondary structure - hydrogen bonds form to make either an alpha helix of beta pleated sheet.
Tertiary structure - more bonds form between different parts of the chain:
# ionic bonds between negative and positively charged r groups
# disulfide bonds between two molecules of cysteine
# hydrophobic and hydrophilic interactions where hydrophilic groups are pushed towards the outside.
# hydrogen bonds between H+ and negatively charged atoms.
Quaternary structure - bonding between different or multiple chains form the last structure. Haemoglobin being made of 4 different chains bonded together.

Question 9

Describe globular and fibrous proteins.

Answer 9

Globular: hydrophilic R groups are pushed to the outside of the molecule. Globular proteins are soluble so they’re easily transported in fluids. Eg. Insulin, haemoglobin and amylase

Fibrous proteins are insoluble, strong, and unreactive. Eg. Collagen,keratin, elastin.

Question 10

How can you test for reducing sugars?

Answer 10

Add Benedict’s reagent and heat in a water bath. Colour of precipitate indicates how much glucose.

Question 11

How do u test for non reducing sugars?

Answer 11

Add dilute HCl and heat in water bath. Add sodium hydrogencarbonate. Add Benedict’s and heat again. Precipitate will form.

Question 12

How do u test for proteins

Answer 12

Add some NaOH to make the mixture alkaline. Add some CuSO4 and observe colour change. If protein present you get a purple solution.

Question 13

How do u test for lipids

Answer 13

Shake with ethanol and pour the solution into water. Lipid present means u see a milky solution.

Question 14

Name purines and pyrimidines.

Answer 14

Purine - 2 rings - adenine, guanine.
Pyrimidine - 1 ring - cytosine, thymine, uracil
A - T has. 2 H bonds
C- G has 3 H bonds.

Question 15

How can you purify DNA from a precipitation reaction?

Answer 15

Break up the cells

Make a solution of detergent (to break the cell membranes) , salt (to bind to the DNA and make it clump up) and distilled water.

Put the mixture in an ice bath to cool it down, filter the mixture.

Add protease enzymes to break down enzymes in the mixture.

Add some cold ethanol down the side and watch the DNA precipitate

Question 16

Describe DNA replication naturally in cells. Why is it called semi conservative.

Answer 16

DNA Helicase breaks the hydrogen bonds between the strands. It unzips.

Each original strand acts as a template for the new strand. Free floating nucleotides come and join up via complementary base pairing.

The nucleotide are joined by DNA polymerase to form a sugar phosphate backbone. New hydrogen bonds form.

It’s called semi conservative because half the strand is from the original and half is new. It’s usually very accurate but occasionally mutations can occur.

Question 17

What are the three types of RNA.

Answer 17

mRNA - made in the nucleus; three adjacent are called a codon; carries the genetic code from the nucleus to the cytoplasm.

tRNA - has an amino acid binding site at one end and a sequence of three bases at the other end called an anticodon. Carries the corresponding amino acid to the ribosome.

rRNA - forms two subunits in a ribosome; helps catalyse the formation of peptide bonds between the amino acids.

Question 18

What is the temperature coefficient and where is it used. Q10?

Answer 18

Shows how much the rate of a reaction changes when the temperature is raised by 10*c. If it has a value of 2 the rate doubles.

Rate at higher temperature / rate at lower temp.

Question 19

What are cofactors and prosthetic groups?

Answer 19

Cofactors enable enzymes to work by binding to their active sites. They aren’t used up or changed. Without the cofactors, the enzymes can’t work. Eg. Cl- cofactors for amylase.

Prosthetic groups are tightly bound cofactors. They are a permanent part of the active site. Eg. Zn+2 is a prosthetic group for carbonic anhydrase.

Question 20

What is end-product inhibition?

Answer 20

When the final product in a metabolic pathway inhibits an enzyme (generally reversibly) that acts earlier on in the pathway. It controls how much product is made.

Inhibition can be reversible or irreversible. Reversible inhibition usually involves ionic or hydrogen bonds. Non reversible inhibition usually involves covalent bonds.

Question 21

What are the components of the phospholipid bilayer and it’s functions?

Answer 21

Phospholipids - act as a barrier for dissolved substances (water soluble) like ions.

Cholesterol - bind to the hydrophobic tails of the phospholipids making them pack closely to regulate fluidity and make it more rigid.

Proteins - control what enters and leaves the cell. Channel proteins allow small or charged particles through. Carrier proteins transport molecules and ions across the membrane. Can act as receptors in cell signalling.

Glycolipids and glycoproteins - stabilise the membrane by forming hydrogen bonds with surrounding water. Act as receptors for cell signalling (binding site for antibodies or drugs). Are also antigens.

Question 22

Outline the action of carrier and channel proteins.

Answer 22

Carrier proteins: facilitated diffusion (passive) or active transport (active).
# facilitated diffusion
1. Large molecule attaches to the carrier protein.
2. Protein changes shape
3. Protein release on the other side.
# Active transport
1. Moves the solute against its concentration gradient.
2. Solute bonds to carrier protein
3. ATP used to move the solute once the protein changes shape

Channel proteins: form pores in the membrane to allow charged particles to diffuse through down the concentration gradient.

Question 23

Describe what happens to animal and plant cells in hypotonic, hypertonic and isotonic solutions.

Answer 23

Hypotonic: solution has a higher water potential than the cell
Isotonic: solution has the same water potential as cell
Hypertonic: solution has a lower water potential than the cell.

Animal:
- hypotonic - cell bursts
- isotonic - no change
- hypertonic - cell shrinks

Plant:
- hypotonic - cell is turgid
- isotonic- no change
- hypertonic - plasmolysis.

Question 24

What is water potential and what has the highest water potential?

Answer 24

Water potential is the potential of water molecules to diffuse in or out of a solution. Pure water has the highest water potential.

Question 25

Describe the cell cycle for mitosis.

Answer 25

1. Interphase:
   - Gap Phase 1 (G1) = cell grows and new organelles and proteins are made.
   - G1 Checkpoint = cell checks that the chemicals needed for replication are present and makes sure there is no damage to DNA before entering S phase.
   - Synthesis phase (S) = cell replicates its DNA ready to divide by mitosis.
   - Gap Phase 2 (G2) = cell keeps growing and proteins needed for cell division are made
   - G2 Checkpoint = checks whether all the DNA has been replicated without any damage, if it passes the cell enters mitosis.
2. Prophase
   - chromosomes condense
   - centrioles move to opposite ends of the cell and form spindle fibres
   - nuclear envelope breaks down
   - in meiosis, chromatids can cross over here.
3. Metaphase
   - chromosomes line up at the middle of the cell.
   - The chromosomes attach to the spindle fibres
4. Anaphase:
   - centromeres divide and the sister chromatids are separated.
   - spindles contract and the chromatids are pulled to opposite ends of the cell.
5. Telophase:
   - nuclear envelope reforms once the chromatids have reached opposite ends of the cell.
6. Cytokinesis
   - cleavage furrow forms and then splits to form the daughter cells.

Question 26

Where is stem cells found in animal and plants?

Answer 26

In animals, it’s found in bone marrow or embryos.
In plants, it’s found in the vascular cambium. It’s specifically called the meristem.