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Biology > 3.1 Biological molecules > Flashcards

3.1 Biological molecules Flashcards

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1
Q

What are the following polysaccharides made up of (include shape):
a) starch
b) glycogen
c) cellulose

A

a) alpha glucose- amylose (helical), amylopectin (branched)
b) alpha glucose (branched)
c) beta glucose (long straight chains)

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2
Q

What are the monosaccharides that make up the following dissacharides:
a) maltose
b) sucrose
c) lactose

A

a) glucose and glucose
b) glucose and fructose
c) glucose and galactose

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3
Q

What makes something a carbohydrate?

A

A molecule made up of carbon, hydrogen and oxygen, with hydrogen and oxygen in the ratio of 2:1

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4
Q

What makes starch hydrolysis slower in cooler environments?

A
  • Controlled by enzymes
  • Less kinetic energy
  • Fewer E-S complexes form as there are fewer successful collisions
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5
Q

Give two features of starch molecules, explain how each one enables starch to act as an efficient storage molecule

A
  1. Starch is insoluble - does not impact water potential in the cell
  2. Starch has a helical structure - compact, can store lots in a small space
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6
Q

How do you test for reducing sugars?

A
  • Add Benedict’s solution
  • Heat
  • Brick red ppt forms
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7
Q

What reducing sugars would you expect to be produced when wheat is chewed. Give a reason for your answer?

A

Maltose
Salivary amylase breaks down starch to maltose.

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8
Q

Why are hydrogen bonds important in cellulose?

A
  • In large numbers they add strength to the molecule
  • Making the cellulose harder to break down
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9
Q

Explain the differences in structure between starch and cellulose molecules.

A
  • Beta glucose in cellulose, alpha glucose in starch
  • Every other glucose molecule in cellulose is inverted
  • Long straight chains in cellulose, helical structure in starch
  • 1,4 -glycosidic bonds in cellulose, mixture of 1,4 and 1,6-glycosidic bonds in starch
  • Cellulose has hydrogen bonds and micro fibril layers, starch does not
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10
Q

Explain how cellulose molecules are adapted to their function.

A
  • Long straight chains of beta glucose which can form hydrogen bonds between the layers and micro fibril layers
  • Adds strength to the molecule in large numbers, strengthens cell wall of plants
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11
Q

Why does orange juice turn brick red and milk turn green after Benedict’s test for reducing sugars?

A
  • Orange juice contains reducing sugars glucose and fructose
  • Milk contains reducing sugar lactose
  • Larger quantities of of reducing sugars in orange juice donate more electrons to Benedict’s solution
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12
Q

Suggest how you can use the Benedict’s test to compare the amount of reducing sugar in two solutions.

A
  • Add equal volumes of Benedict’s solution to both samples and heat (standardise condition)
  • Compare the colour of ppt that forms, brick red has more reducing sugars present
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13
Q

How do you carry out the Benedict’s test for non-reducing sugars?

A
  • Carry out test for reducing sugars and obtain a negative result
  • Then add HCl to a new sample and heat
  • Then add sodium hydrogencarbonate
  • Add Benedict’s solution and heat
  • Brick red ppt is positive result
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14
Q

Why does table sugar turn brick red after Benedict’s test for non-reducing sugars?

A
  • Table sugar contains sucrose, a non-reducing sugar
  • 1,4 glycosidic bond hydrolysed by HCl
  • Releases reducing sugars glucose and fructose
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15
Q

Compare and contrast the structure of triglycerides and phospholipids.

A

Similarities:
- Both have glycerol and fatty acids covalently bonded together
- Both have ester bonds formed by condensation reaction
- Both can have (un)saturated fatty acids
- Both are macromolecules containing H, C and O

Differences:
- Phospholipid has hydrophobic/hydrophilic parts, triglyceride has only hydrophobic fatty acid tails.
- Phospolipid has 2 fatty acids and a phosphate, triglyceride has 3 fatty acids

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16
Q

How do you test for a lipid?

A
  • Dissolve sample in ethanol then add water and shake
  • Positive result = milky emulsion forms
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17
Q

How do you test for proteins?

A
  • Biurets solution
  • Turns purple from blue
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18
Q

What is the bond present in a protein?

A

Peptide

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19
Q

Describe each of the following structures of a protein:
a) primary
b) secondary
c) tertiary
d) quaternary

A

a) sequence of amino acids
b) the folding of polypeptide chains by hydrogen bonds (alpha helices, beta pleated sheets)
c) bonds (ionic, hydrogen, disulphide bridges, hydrophobic interactions) between amino acids, producing overall 3D shape
d) when two or more polypeptides bond together to form the protein, includes any prosthetic groups

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20
Q

What are the differences between globular and fibrous proteins?

A
  • Globular have a quaternary structure, fibrous have a secondary structure
  • Globular have metabolic, fibrous have structural roles
  • Globular are soluble/unstable, fibrous are insoluble/stable
  • Globular are spherical shapes, fibrous are long strands
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21
Q

Give examples of two globular and two fibrous proteins.

A

Globular: haemoglobin, insulin
Fibrous: actin, collagen

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22
Q

How do enzymes lower the Ea required for a reaction to start?

A
  • Enzyme active site has complimentary shape to substrate
  • Binds to substrate and applies pressure to bonds, causing them to vibrate
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23
Q

How is the Induced Fit hypothesis different to the Lock and Key model?

A

Induced Fit hypothesis only has a partially complimentary active site and the active site can change shape

24
Q

What are the problems with the Lock and Key model?

A

-Active site is rigid so the enzyme cannot apply pressure to bonds causing the molecule to spilt or polymerise

25
Q

Explain how a substrate is broken down by an enzyme.

A
  • Enzyme has complimentary active site shape to the substrate
  • Substrate able to bind to active site
  • E-S complex formed
  • Bonds broken, smaller molecules formed
26
Q

Why can an enzyme catalyse one reaction but not another?

A
  • Enzyme has active site shape that is only complimentary to the shape of some substrates
  • Not all substrates can fit and from E-S complexes
27
Q

Explain how an non-competitive inhibitor works.

A
  • Molecule binds to allosteric site on enzyme
  • Change in primary structure and then tertiary structure, ionic/hydrogen bonds break
  • Active site shape changes and substrate is no longer complimentary
  • Fewer E-S complexes
28
Q

Explain how a competitive inhibitor works.

A
  • Molecule has similar shape to substrate so can bind to active site
  • This blocks substrate from binding
  • Fewer E-S complexes form
29
Q

Explain how adding excess substrate can overcome the effect of a competitive inhibitor.

A
  • Higher ratio of substrate to inhibitor
  • More likely substrate will collide with enzyme so more E-S complexes form
30
Q

Why does increasing substrate concentration sometimes fail to increase rate of reaction?

A
  • Substrate in excess
  • Enzyme active sites all occupied, enzyme is the limiting factor
31
Q

Explain the importance in maintaining a constant blood pH.

A
  • Enzymes have optimum pH
  • If the pH rises or falls then the concentration of OH- and H+ ions changes
  • This will disrupt the ionic and hydrogen bonds in the tertiary structure of proteins
  • Changes shape of active site so no longer complimentary
  • Fewer E-S complexes form
32
Q

Why do enzymes usually denature at hotter temperatures ( >40°C) ?

A
  • Increase in KE
  • Disrupts tertiary structure and the hydrogen/ionic bonds and disulphide bridges
  • Active site of enzyme changes shape, no longer complimentary
  • Fewer E-S complexes can form
33
Q

What is ATP? What is it made up of?

A

Adenosine Triosephosphate
- A high energy, phosphorylated molecule
- 3 phosphate groups, ribose sugar, adenine base

34
Q

Why is it dangerous to store ATP in cells?

A

ATP is extremely unstable and will give the Pi to anything

35
Q

How much energy is released when ATP is hydrolysed?

A

30.5 kJ mol-1

36
Q

Why is ATP unstable?

A

As each -ve charge phosphate is added there is an increase in negative repulsions

37
Q

How is ATP hydrolysed?

A

ATPase: ATP → ADP + Pi
releases energy

38
Q

How is ATP synthesised?

A

ATP synthase: ADP + Pi → ATP
requires energy (respiration)

39
Q

What is a reaction involving the Pi called?

A

Phosphorylation

40
Q

Give 2 ways in which ATP is made a suitable source of energy is biological processes.

A
  1. Readily hydrolysed and synthesised in a single reaction
  2. Only releases small packets of energy, so little energy loss through heat
41
Q

Give 2 advantages of ATP as an energy-storage molecule within a cell.

A
  1. Releases small packets of energy, so little energy is lost as heat
  2. Can’t leave the cell as it is highly polar
42
Q

Why do humans have to synthesise more than their body mass of ATP each day?

A
  • ATP is very unstable so can’t be stored in cells
  • ATP only releases small packets of energy (30.5 kJ mol-1)
43
Q

Name structural differences between RNA and DNA.

A
  • RNA has uracil, DNA has thymine
  • RNA has a ribose sugar, DNA has a deoxyribose sugar
  • DNA is double stranded, RNA is single stranded
  • DNA has hydrogen bonds, RNA does not
  • DNA is relatively long, RNA is shorter
44
Q

What bond forms along the phosphate sugar backbone and how?

A

Phosphodiester bond
DNA polymerase

45
Q

What are the differences between prokaryotic and eukaryotic DNA?

A
  • Prokaryotic DNA is not associated with histones, eukaryotic is
  • Prokaryotic DNA is circular, eukaryotic is linear
  • Prokaryotic DNA has no introns, eukaryotic has introns
46
Q

What bases are purines and pyramidines?

A

Purines: A+G
Pyramidines: T+C

47
Q

How many hydrogen bonds form between each of the complimentary base pairs?

A

G-C = 3
A-T = 2

48
Q

In what direction are nucleotides joined by DNA polymerase and why?

A
  • joined from the 5’ end to the 3’ end
  • DNA polymerase has a specific active site shape that can only bind to the 5’ end
  • the 5’ end and 3’ end are different shapes, only 5’ is complimentary
49
Q

How does semi-conservative replication occur?

A
  • DNA helicase breaks hydrogen bonds between bases
  • produces two template strands with exposed bases
  • DNA nucleotides line up along complimentary bases
  • DNA polymerase runs along strands, joining new nucleotides
  • phosphodiester bonds form and sugar phosphate backbone created
  • two new complimentary DNA strands are formed
50
Q

What evidence is there to support the semi-conservative theory of replication?

A
  • Heavy DNA (N15) and normal DNA (N14) used by scientists
  • produced hybrid DNA from both and centrifuged each generation
  • observed the bands that formed at each generation
51
Q

What are 6 important properties of water?

A
  1. High latent heat of vaporisation:
    helps organisms cool down (sweating/panting)
  2. High specific heat capacity:
    little fluctuations in water temp, aquatic environment more stable as it requires lots of energy for temp of water to increase by 1°C
  3. Universal solvent:
    many molecules able to be absorbed and transported around organism (xylem, phloem)
  4. Cohesion of molecules:
    water able to move up xylem
  5. Transparent medium:
    light able to pass through to photosynthesising organisms below (algae), supporting aquatic ecosystems
  6. Good reaction medium:
    cytoplasm in cells is the site of many important cellular reactions
52
Q

What is the role of the phosphate ion in organisms?

A
  • ATP, ADP and phosphorylation
  • DNA and RNA in nucleotides
53
Q

What is the role of iron in organisms?

A

Prosthetic group in haemoglobin, 4 iron atoms for 4 oxygen molecules

54
Q

What is the role of hydrogen in organisms?

A

H+ plays a large role in the pH of solutions, have to have optimum pH for enzyme activity etc.

55
Q

What is the role of sodium in organisms?

A

Co-transport of sodium with glucose/amino acids at epithelial cells lining small intestine

Biology (10 decks)

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