B1.1 Carbohydrates and Lipids

Question 1

What is the use of carbon?

Answer 1

Without it life would not exist. carbon atoms can each form covalent bonds, forming a chain of any length.
- Stables molecules are produced, covalent bonds are the strongest type of bond.

Question 2

Examples of carbon forming covalent bonds

Answer 2

Carbon can bind with 4 atoms of one other element, such as hydrogen atoms to form methane. And can also bond with more than one other element, oxygen and hydrogen to form ethanol.

Question 3

How many carbons can fatty acids hold up to?

Answer 3

Fatty acids contain unbranched chains of up to 20 carbon atoms, chains can also be branched. With the branch often made using an oxygen atom.

Question 4

Single covalent bonds allow the bonded atoms to?

Answer 4

To be able to rotate, but not to move further apart or nearer to each other, covalent bonds spread apart as much as possible to form a tetrahedral shape.

Question 5

Why is the chain of carbon bonds not straight?

Answer 5

Due to the bond angles, they can form rings, the ring can be made entirely of carbon atoms, or contain another element.

Question 6

What are macromolecules

Answer 6

Molecules composed of a large number of atoms, main classes are polysaccharides, polypeptides, and nuclei acids. Made by linking together subunits (monomers) in a chain (polymers). Linked by a condensation reaction.

Question 7

What happens in a condensation reaction?

Answer 7

Two molecules are linked together, a smaller molecule is released. When psaccharides, ppeptides and n acids are constructed, simpler molecule is water.

Produced by removing a hydroxyl group (-OH) from one of the molecules being linked, and a hydrogen from the other, allowing a bond to be made to bridge the molecules.

Question 8

Energy is…

Answer 8

Required to construct polysaccharides, polypeptides and nucleic acids, the energy is supplied by ATP.

Question 9

What is a disaccharide, and polysaccharide?

Answer 9

Disaccharide is two monosaccharides linked together. Polysaccharide is a chain of monosaccharides. Glucose is the monosaccharide used to make glycogen, starch and cellulose.

Question 10

What bonds link the glucose molecules together?

Answer 10

Lined with glycosidic bonds, C-O-C linkages formed by condensation using hydroxyl groups.

Hydroxyl in C1 of glucose is linked to hydroxyl on C4 at the end of the growing chain. In an unbranched chain, all glycosidic bonds are 1->4. There are also 1->6 bonds.

Question 11

How do we form branches?

Answer 11

To form branches, C1 of a glucose is linked to the C6 of a glucose in the chain. This 1->6 linkage forms a side branch, more glucose molecules can be added to it with 1->4 bonds.

Question 12

Cellulose contain unbranched chains of what type of glucose?

Answer 12

Cellulose molecules are unbranched chains of Beta (β) glucose that contain 15,000 glucose molecules,

Question 13

What type of glucose is glycogen made out of in liver/muscle cells?

Answer 13

Glycogen in liver or muscle cells are branched chains of alpha (α) glucose, with up to 60,000 molecules.

Question 14

What is a hydrolysis reaction?

Answer 14

Water molecules are split to provide hydrogen and hydroxyl groups, used to make bonds to replace bond that has been broken. used to deconstruct polysaccharides, polypeptides and nucleic acids into monosaccharides, amino acids and nucleotides.

Polymers can be deconstructed so the monomers can be reuse to build new polymers or used as a source of energy.

Question 15

Where does hydrolysis occur?

Answer 15

This occurs in digestion. Digestion of these polymers can be carried out by all cells, and also happens in the gut.

Decomposers release digestive enzymes into environment around them to break down polymers by hydrolysis, so they can absorb and use monomers.

Question 16

What is the form of monosaccharides?

Answer 16

have between 3 and 7 carbon atoms, pentoses, hexoses (5, 6), Pentoses and hexoses normally have a ring of atoms, one oxygen atom in the ring and rest is C atoms.

Question 17

Examples of energy stores

Answer 17

Starch is used in plants, glycogen in animals, both substances are composed of large numbers of alpha glucose molecules, which can be used as a substrate in aerobic and anaerobic cell respiration.

• Glucose can be removed from starch + glycogen when needed
• hydrolysis reaction breaks 1->4 glycosidic bond to separate one glucose molecule from end of a chain
• allowing it to be transported elsewhere or in cell.

Question 18

What are the two types of starch molecules?

Answer 18

Amylose, unbranched chain of glucose linked by 1->4 glycosidic bonds, bond angle makes it helical.

Amylopectin, same structure as amylose, but have 1->6 glycosidic bonds, making molecule branched.

adding/removing glucose happens more quickly with amylopectin than amylose, as branched structure provides more ends of chains.

Question 19

Explain how glycogen and amylopectin have similar structure.

Answer 19

alpha glucose molecules linked by 1->4 glycosidic bonds, branched by 1->6 bonds. Glycogen more branched. makes them relatively compact, despite huge molecular mass.

Very large size gives much lower solubility, contributes little to the osmotic concentration of cells. Can be used to store large amounts of glucose without cell swelling or with water draw in by osmosis.

Question 20

What is a consequence of limitless addition/removal of glucose?

Answer 20

Limitless addition/removal of starch + glucose causes them to not have a fixed molecular mass, so molar solutions cannot be made. Concentrations have to be expressed in % terms (grams of a substance per 100cm^3 of solution).

Question 21

Structure of cellulose?

Answer 21

Cellulose, composed of beta glucose.
Condensation reactions links C1 on a free glucose molecule to C4 on the beta glucose at the end of the growing cellulose molecule. All links are 1->4 glycosidic bonds, unbranched chain.

In beta glucose, the hydroxyl group on C1 is angled upwards, and hydroxyl group on C4 is angled downwards. To bring these -OH groups together and allow condensation to occur, each beta glucose added to the chain has to be inverted in relation to previous one.
Glucose subunits in chain therefore face alternately up and down.

Question 22

What are bundles of cellulose called?

Answer 22

These bundles of cellulose are called microfibrils, the basis of plant cell walls.
Microfibrils have high tensile strength, strong covalent bonds in cellulose molecules, and cross links between them.
Prevents plant cells from bursting, even when very high pressures develop due to osmosis when water enters.

Question 23

What are glycoproteins?

Answer 23

Composed of polypeptides with carbohydrate attached (oligossacharide)
- glycoproteins are a component of plasma membranes in animal cells, and are positioned with attached carb facing outwards.

Question 24

Use of glycoproteins?

Answer 24

By displaying distinctive glycoproteins, cells allow other cells to recognise them, glycoprotein on surface of one cell is recognized by receptors on surface of another cell.

Question 25

How does cell to cell recognition help?

Answer 25

Helps with organization of tissues and can also allow foreign cells/infected body cells to be identified and destroyed. The ABO antigens in red blood cells are an example of glycoproteins.

Question 26

What do red blood cells have in their membranes?

Answer 26

Glycoproteins, but do not have a known function, except affecting blood transfusion (donating blood), three types of oligosaccharides can be present in glycop. O, A ad B. One or two of these types are present in every person’s blood, but not all three.

Question 27

What happens if blood containing glycoprotein A is transfused into a person who does not produce it themself?

Answer 27

Blood will be rejected, this will also happen if glycoprotein B is transfused into a person who doesn’t produce it.
- Blood type O does not cause rejection problems, has same structure as A and B with one monosaccharide less, not recognised as foreign.

Question 28

What are the hydrophobic properties of lipids:

Answer 28

Lipids are a group of substances in living organisms that dissolve in non-polar solvents. Lipids are only sparingly soluble in aqueous solvents, more attracted to non-polar substances.

Question 29

What are the melting points of oils, fats and waxes?

Answer 29

• oils have melting point below 20 degrees Celsius, so solidify at low temperatures.
  = Fats have melting point between 20 and 37 degrees Celsius so they are solid at room temp and liquid at body temp.
• waxes have a melting point above 37 degrees celsius, so they liquify at high temp.

Question 30

What is a triglyceride?

Answer 30

Made by combining three fatty acids with one glycerol. Each of the fatty acids is linked to the glycerol by a condensation reaction, so three water molecules are produced.

Question 31

What is the name of the linkage formed between each fatty acid and the glycerol (to form a triglyceride)?

Answer 31

Ester bond, formed when an acid reacts with alcohol. Reaction between the carboxyl group (-COOH) on a fatty acid and a hydroxyl on glycerol. These groups are the only hydrophilic parts of fatty acid and glycerol molecules. they are used up in the condensation reaction, so triglycerides are entirely hydrophobic.

Question 32

Difference between phospholipids and triglycerides in terms of structure?

Answer 32

There are two fatty acids linked to glycerol, with a phosphate group instead of a third fatty acid. The phosphate is hydrophilic, so phospholipid molecules are partly hydrophilic and partly hydrophobic.

Question 33

Fatty acids have what chain?

Answer 33

A chain of unbranched carbon atoms, with hydrogen atoms covalently bonded, this is a hydrocarbon chain. acid part of molecule is a carboxyl group at one end of, other end is a methyl group.

Question 34

What is variable about fatty acids?

Answer 34

Length is variable, but most fatty acids used by living organisms have between 14-20 carbon atoms.
Another variable is in the covalent bonds between carbon atoms, some have single bonds between all carbona toms, whereas others have double bonds between some pairs of carbons atoms in the chain.

Single bonds can also bond to hydrogen atoms, carbon atoms linked by double bonds to an adjacent carbon in the chain can only carry one hydrogen.

Question 35

Fatty acids with single bonds are what type of fatty acid?

Answer 35

fatty acids with single bonds between all of its atoms contain as much hydrogen as it possibly could and is called a saturated fatty acid.

Question 36

Fatty acids with one or more double bonds are?

Answer 36

Unsaturated, they contain less hydrogen than they could, if there is one double bond, fatty acid is monounsaturated; if it has more than one double bond, it is polyunsaturated.

Question 37

Nearly all unsaturated fats are cis fatty acids, what are cis fatty acids?

Answer 37

1) Hydrogen atoms on the same side of the double bonded carbon atoms. Causes a bend in the hydrocarbon chain.
2) Triglycerides with cis fatty acids less good at packing together in regular arrays, thus low melting point.
3) Triglycerides with cis-unsaturated fatty acids are usually liquids at room temp, they are oils.

Question 38

What is the alternative arrangement for cis fatty acids?

Answer 38

Alternative arrangement is for the hydrogens to be on the opposite sides, these are trans fatty acids. They do not have a bend in the hydrocarb chain at the double bond, they have straight chains and a higher melting point, being solid at room temp.

Question 39

How are trans fatty acids produced?

Answer 39

Produced artificially by partial hydrogenation (chemical reaction between hydrogen and an element/ compound, in the presence of a catalyst). This is done to produce solid fats for use in margarine and other processed food. But the FDA in the US has banned use of industrial trans fats due to serious health concerns.

Question 40

What are triglycerides used for?

Answer 40

Used for energy storage in plants and animals. In animals, triglycerides are fats and are stored in specialised groups of cells called adipose tissue. In humans, adipose tissue is located beneath the skin and also some organs including kidneys.

Question 41

What are the properties of triglycerides that make them particularly suitable for long term energy storage?

Answer 41

• Chemically stable, energy is not lost over time.
• Immiscible with water, naturally form droplets in cytoplasm which do not have osmotic or other effects on cell.
• release twice as much as energy/gram in cell respiration than carbohydrate. So enough energy can be stored in half the body mass.
• poor conductors of heat, can be used as a thermal insulator in animals that need to conserve body heat.
• liquid at room temperatures, can act as a shock absorber, for e.g around kidneys.

Question 42

Why is thermal insulation needed most by animals?

Answer 42

Needed for animals that live in cold habitats and that maintain body temperature much higher than environment.
- these animals have thick layers of subcutaneous adipose tissue. Marine animals call this blubber, in animals such as sea lions, there are sometimes problems with overheating when adults emerge onto land to breed. Because thick layer of blubber impedes dissipation of heat produced by metabolism and air is much warmer than water.

Question 43

What are substances attracted to water called?

Answer 43

Hydrophilic

Question 44

Other substances not attracted to water?

Answer 44

Hydrophobic.

Question 45

Why are phospholipids unusual?

Answer 45

They contain both a hydrophilic head, and a hydrophobic tail. They are described as amphipathic. Hydrophilic head is the phosphate group, hydrophobic part consists of two hydrocarbon chains.

Question 46

What happens when phospholipids are mixed with water?

Answer 46

Phosphate heads are more attracted to water, hydrocarbon tails are attracted to one another more than the water, because of this phospholipids beocme arranged into double layers, with hydrophobic hydrocarbon tails facing inwards, hydrophilic heads facing outwards to water. These double layers are called phospholipid bilayers, they are stable and form basis of all cell membranes.

Question 47

Explain what the ability of non-polar steroids are?

Answer 47

Hundreds of different steroids differ in the position of C = C double bonds and in functional groups, such as -OH that are added to the four ring structure.
Steroids are mostly hydrocarbon and therefore hydrophobic, allowing them to pass through phospholipid bilayers and enter/leave cells.

Question 48

What are steroids?

Answer 48

Group of lipids with molecules similar to sterol, can be identified by:
- four fused rings of carbon atoms
- three cyclohexane rings and one cyclopentane ring
- 17 carbon atoms in total in the rings.

Question 49

What is the structure of glucose?

Answer 49

Always a hydroxyl group and one hydrogen group on C1, upper group is -H in alpha glucose and -OH in beta glucose.

Question 50

Function of monosaccharides? e.g glucose

Answer 50

1) Soluble and relatively small, easily transported. Dissolved in blood plasma.
2) Chemically stable for food storage. Osmotic problems occur when stored in large quantities, and is converted.
3) Yields energy when oxidised, used as a substrate for respiration.