Biological molecules Flashcards
2 marks
Two proteins have the same number and type of amino acids but different tertiary box
structures.
Explain why.
- Different primary structure
- Forms ioninic/ disulfide/ hydrogen bonds in different places
2 marks
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end.
- One amine group joins to a carboxyl group to form a peptide bond
- So in chain there is a free amine group at one end and a free carboxyl group at the other
4 marks
Describe how the structure of glycogen is related to its function.
- Helical so compact
- Polymer of glucose so easily hydrolysed
- Branched so more ends for faster hydrolysis
- Glucose polymer so provides respiratory substrate for energy release
- Insoluble so no osmotic effect
4 marks
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein
- Glucose and galactose
- In a condensation reaction
- Joined by glycosidic bond
- Added to a polypeptide in golgi body
3 marks
How to test for non-reducing sugar
Heat with acid and neutralise
Heat with benedicts
If present red precipitate formed
3 marks
Differences between phospholipid and triglyceride
- 3 fatty acids rather than 2;
- 3 ester bonds rather than 2;
- No phosphate group;
Unsaturated fatty acids bonds
Double bonds present between carbon atoms
Unsaturated fatty acids cause bends/kinks in fatty acid tail
Presence of double bonds decreases number of hydrogens presnt in fatty acids
3 marks
A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how.
- Inhibitor similar shape to substrate
- Binds to active site
- Less enzyme-substrate complex forming
3 marks
When bread becomes stale, the structure of some of the starch is changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could help to reduce weight gain.
- Less hydrolysis of starch
- To maltose
- Less absorption of glucose
4 marks
Give two reasons why glucose uptake by muscle cells increases significantly during exercise. Explain your answers
- Increased respiration;
- To provide more ATP for muscle contraction;
- (More glucose being used so) concentration gradient for glucose
- (Glucose enters by) facilitated diffusion;
Describe the structure of both a sucrose-transport protein and a glucose-transport protein?
The secondary structure is held by hydrogen bonds.
The tertiary structure allows the protein to be positioned spanning the whole cell membrane.
3 marks
Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria
- 1/10 dilution is made by 1 part liquid culture, 9 parts of water
- Mix, repeat 2x
- 1 part of 1/10 dilution, 9 parts of water = 1/100 dilution
- 1 part of 1/100 dilution, 9 parts of water= 1/1000 dilution
4 marks
Describe how to make a temporary mount
- Add drop of water to glass slide
- Obtain thin section of specimen and place on glass slide
- Stain with iodine
- Lower cover slip using mounted needle
5 marks
Describe the structure of DNA.
- Polymer of nucleotides
- Each nucleotide formed from deoxyribose, a phosphate group and a nitrogenous base
- Phosphodiester bonds between nucleotides
- Double helix
- Hydrogen bonds between complementary base pairings= adenine, thymine and cytosine, guanine
4 marks
Explain how ATP is a suitable energy source for cells to use
- Immediate source of energy/ releases energy immediately
- Little energy lost as heat
- Doesnt leave cells
- Phosphorylates other compounds, making them more reactive
2 marks
Explain the property of water that can help to buffer changes in temperature.
- High specific heat capacity
- Can lose a lot of heat without changing temperature
5 marks
Describe the roles of iron ions, sodium ions, and phosphate ions in cells
Iron ions
1. Haemoglobin binds with oxygen
Sodium ions
2. Co-transport of glucose/amino acids into epithelial cells
3. Because sodium moved out by active transport/Na – K pump
4. Creates a sodium concentration gradient
5. Affects osmosis/water potential
Phosphate ions
6. Affects osmosis/water potential;
7. Joins nucleotides held by phosphodiester bond in sugar phosphate backbone of nucleotides
8. Used to produce ATP
9. Phosphorylates other compounds making them more reactive
10. Hydrophilic part of phospholipid bilayer
2 marks
Describe the structure of glycogen
- Polymer of alpha glucose
- Joined by glycosidic bonds
2 marks
Suggest how glycogen is used as a source of energy
- Hydrolysed to glucose
- Glucose is used in respiration
5 marks
Describe the structure of DNA
- Polymer of nucleotides
- Each nucleotide formed from deoxyribose, a phosphate group and a nitrogenous base
- Phosphodiester bonds between nucleotides
- Double helix held by hydrogen bonds
- Hydrogen bonds between complementray base pairings: adenine, thymine and cytosine, guanine
5 marks
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.
Lipid
1. Add ethanol then add water and mix
2. White milky emulsion
Non-reducing sugar
3. Do Benedict’s test and stays blue
4. Boil with acid then neutralise with alkali
5. Heat with Benedict’s and becomes red
Amylase
6. Add biuret reagent and becomes purple
7. Add starch, leave for a time, test for reducing sugar
2 marks
Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how.
- Reduces activation energy
- Due to bending bonds
5 marks
Mucus produced by epithelial cells in the human gas exchange system contains
triglycerides and phospholipids.
Compare and contrast the structure and properties of triglycerides and phospholipids.
- Both contain ester bonds
- Both contain glycerol
- Fatty acids on both may be saturated or unsaturated
- Both are insoluble in water
- Both contain C, H and O but phospholipids also contain P
- Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group
- Triglycerides are hydrophobic and phospholipids have hydrophilic and hydrophobic
- Phospholipids form bilayer but triglycerides don’t
4 marks
Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached.
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.
- Glucose and galactose
- Joined by condensation reaction
- Joined by glycosidic bond
- Added to polypeptide in Golgi apparatus
