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Biology > 1. Biological molecules > Flashcards

1. Biological molecules Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is a monomer?

A

Small molecules used in the making of larger, more complex molecules (polymers)

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2
Q

What is a polymer?

A

A larger molecule made from the joining of many monomers (via. condensation reactions)

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3
Q

Name examples of monomers

A

Monosaccharides, amino acids and nucleotides

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4
Q

What is a condensation reaction?

A

A reaction by which multiple monomers/smaller molecules are joined together by a chemical bond to make a polymer/larger molecule, involving the release of water molecules

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5
Q

What is a hydrolysis reaction?

A

The breaking down of a polymer/larger molecules into its monomers (smaller molecules) by the addition of water

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6
Q

How is a disaccharide formed?

+ example

A

By the condensation of two monosaccharides, joined by a glycosidic bond
For example, a condensation reaction between 2 alpha glucose molecules will involve them forming an alpha 1-4 glycosidic bond (between the C1 atom on one glucose and the C4 atom of the adjacent glucose molecule)

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7
Q

What is maltose?

A

A disaccharide formed by the condensation of two alpha glucose molecules

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8
Q

What is lactose?

A

A disaccharide formed by the condensation of a glucose and a galactose molecule

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9
Q

What is sucrose?

A

A disaccharide formed by the condensation of a glucose and a fructose molecule

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10
Q

What are the two isomers of glucose?

+ draw to check I know them

A

Alpha glucose and beta glucose

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11
Q

What is a polysaccharide?

A

A large molecule formed by the condensation of many monosaccharides

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12
Q

Explain the structure of glycogen

A

Chains of alpha glucose - both 1-4 and 1-6 glycosidic bonds however there are less 1-4 bonds and more 1-6, resulting in a more branched, compact structure with shorter chains

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13
Q

Where is glycogen found?

A

In animal and bacteria, but not plant cells

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14
Q

How does the structure of glycogen relate to its role of energy storage?
(3)

A
  • It is insoluble and therefore doesn’t diffuse out of cells
  • Compact structure means that a lot can be stored in small amounts of space
  • Its branched structure means the ends can be acted on simultaneously by enzymes, releasing glucose more rapidly (rapid release of energy)
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15
Q

Explain the structure of cellulose

A

Chains of beta glucose - every other glucose molecule is flipped 180 degrees to allow the 1-4 glycosidic bonds to form
The beta glucose chains run parallel to one another to form long, straight, unbranched chains
Hydrogen bonds form between the OH groups on adjacent parallel chains to form cross linkages

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16
Q

What is the role of cellulose?

A

The main role of cellulose is a structural/support role
It is also an important part of plant cell walls as it provides rigidity and prevents plant cells from bursting when water enters by osmosis (important for maintaining turgidity of the plant)

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17
Q

How does the structure of cellulose relate to its structural/support role?

A

Cellulose molecules group together to form microfibrils
These microfibrils are arranged in parallel groups called fibres, which form a criss-cross mesh that then makes up the cell walls in plants, which adds to the structural stability

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18
Q

Explain the structure of starch

A

Starch is made up of 2 polysaccharides - amylose (20%) and amylopectin (80%)
Amylose is formed from alpha 1-4 glycosidic bonds, giving starch a coiled structure
Amylopectin is made of alpha 1-4 and alpha 1-6 glycosidic bonds, and the 1-6 bonds give starch a slightly branched structure

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19
Q

How does the structure of starch relate to its function of energy storage? (5)

A
  • It is insoluble and so doesn’t affect water potential
  • It is large and insoluble so doesn’t diffuse out of cells
  • Compact structure allows a lot to be stored in a small amount of space
  • When hydrolysed it forms alpha glucose, which can be readily used in respiration
  • The branched ends can be acted on simultaneously by enzymes for rapid release of glucose/energy
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20
Q

What is the test for reducing sugars and how is it carried out?
What causes the colour change?

A

The Benedict’s test:

  • Add 2cm³ of the sample to a test tube
  • Add an equal volume of Benedict’s reagent
  • Heat in a gently boiling water bath for 5 minutes
  • If a reducing sugar is present, a colour change of blue to brick red will be observed

The colour change is caused by the copper (II) sulphate of the Benedict’s solution being reduced and forming copper (I) oxide
Colours other than red (semi-quantitative results) may also be observed

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21
Q

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

A
  • After the Benedict’s test was carried out and resulted in no change, take 2cm³ of the food sample and add 2cm³ of HCl
  • Place in a gently boiling water bath for 5 minutes - the dilute HCl will hydrolyse the disaccharide into its constituent monosaccharides
  • Slowly add sodium hydrogencarbonate to neutralise the HCl
  • Retest the resulting solution with 2cm³ of Benedict’s solution
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22
Q

What is the test for starch and how is it carried out?

A

The iodine test:

  • Add 2 drops of iodine to 2cm³ of a sample in a test tube
  • Shake or stir the solution
  • In the presence of starch, the solution will turn from orange to blue/black
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23
Q

What are the two types of lipids?

A

Triglycerides and phospholipids

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24
Q

Explain how triglycerides are formed

A

3 fatty acids each form an ester bond with glycerol (draw!) via. condensation reactions

25
Q

How is the structure of triglycerides related to its properties?

A
  • They are an excellent source of energy due to the high ratio of carbon-hydrogen bonds - when oxidised, they provide more than twice the amount of energy as the same amount of carbohydrate
  • Being large and non-polar, triglycerides are insoluble in water and therefore their storage doesn’t affect water potential in cells or osmosis
26
Q

Explain the structure of phospholipids

A

Phospholipids have a similar structure to triglycerides, except that one of the fatty acids is substituted by a phosphate group
A phospholipid is made up of 2 parts:
- hydrophilic head - interacts with water, not fats/organic solvents
- hydrophobic tail - interacts with fats/organic solvents, but orients themselves away from water
This makes a phospholipid polar

27
Q

What is the role of phospholipids?

A
  • Contributing to the flexibility of cell membranes and the transfer of lipid-soluble substances across membranes
  • Phospholipids either group to form micelles or a phospholipid bilayer due to their structure
  • Useful in waterproofing due to the majority being hydrophobic/insoluble in water
28
Q

Describe a saturated fatty acid

A
  • Only contain C-C bonds - linear hydrocarbon chain
  • Pack closely together
  • Strong attractions between the chains, leading to a higher melting point (solids at room temperature)
29
Q

Describe an unsaturated fatty acid

A
  • One or more C=C bond, causing the hydrocarbon chains to bend
  • Fatty acid molecules therefore cannot pack closely together
  • Weaker and fewer attractions between chains, leading to a lower melting point (liquids at room temperature)
30
Q

What is the test for lipids and how is it carried out?

A

The emulsion test:

  • Mix 2cm³ of the sample being tested with 5cm³ of alcohol (eg. ethanol) in a test tube
  • Shake the tube thoroughly
  • Add 5cm³ of cold water and shake gently
  • If a lipid is present, the solution will change from colourless to cloudy white
  • As a control, repeat the procedure with water instead of the sample and the solution will remain colourless
31
Q

Describe the structure of an amino acid

+ draw

A

Amino acids are the smaller molecules from which a protein is made
Each amino acid has a central carbon atom attached to 4 different chemical groups:
- Amino group (NH2)
- Carboxyl group (COOH)
- Hydrogen atom
- R group (variety of different R groups, each unique to the different amino acid)

32
Q

How is a peptide bond formed?

A

Through a condensation reaction in which the OH group from the carboxyl group of one amino acid is combined with a hydrogen from the amino group of another amino acid
A protein can be made up of one or more polypeptide chain

33
Q

What is the process of forming a polypeptide chain called?

A

Polymerisation

34
Q

State and explain the 4 types of R groups

A
  • Thiol (containing sulphur)
  • Ionic (charged)
  • Hydrophilic (OH groups)
  • Hydrophobic (not polar or charged)
35
Q

Primary structure

A

The sequence of amino acids within a polypeptide chain
The protein’s primary structure is what determines its final shape and therefore its function - therefore a protein’s shape is very specific to its structure

36
Q

Secondary structure

A

Weak hydrogen bonds form between the slight positive hydrogen in the N-H group of one amino acid and the slight negative oxygen in the C=O group of another (due to their polarity)
This pulls the polypeptide chain into either an alpha helix coil or beta pleated sheets - both can be found in one polypeptide chain

37
Q

Tertiary structure

A

Further twisting and folding of the polypeptide chain to give the complex and very specific structure of the protein
This structure is maintained by different bonds between the R groups (therefore where these bonds occur depends on the protein’s primary structure):
- Disulphide bridges
- Ionic bonds
- Hydrogen bonds
- Hydrophobic interactions

38
Q

Quaternary structure

A

The association between more than one polypeptide chain - held together by the same 4 types of bonds as in the tertiary structure
There may also be non-protein groups, called prosthetic groups, associated with the polypeptide chains, ultimately forming the protein

39
Q

Describe what a globular protein is and their functions/properties

A

A protein folded into a ball shape with a compact structure - they carry out metabolic functions
The hydrophobic R groups are found on the inside of the structure meaning they can form hydrophobic interactions with one another to hold the structure
The hydrophilic R groups are found on the outside, therefore globular proteins are soluble in water

40
Q

Give/describe an example of a globular protein

A

Haemoglobin

  • 4 chains (one pair of alpha, one of beta)
  • The prosthetic ring structure has an iron ion in the centre - one associated with each polypeptide chain)
41
Q

Describe what a fibrous protein is and their functions/properties

A

Long chains/strands running parallel to one another
They are linked by cross-bridges so are very strong and stable
The R groups all stick out, making them insoluble in water
They are fibre-like and have structural functions

42
Q

Give/describe an example of a fibrous protein

A

Collagen

  • 3 polypeptide chains wound together in an alpha helix coil
  • Found in fibrous tissue eg. tendons
  • Very strong (when muscle contracts, it pills the bone in the same direction
  • Has a little bit of stretch
43
Q

What is the test for proteins and how is it carried out?

A

Biuret test:

  • Mix your sample with the Biuret’s reagent (sodium hydroxide and a few drops of dilute copper (II) sulphate solution)
  • A colour change of blue to purple/violet indicates the presence of peptide bonds and hence, a protein
  • The darker the colour, the more peptide bonds present, because the N atoms in the peptide bonds form a purple complex with the copper (II) sulphate
44
Q

What is an enzyme and how does it work?

A

Enzymes are globular proteins that act as catalysts

They work by lowering the activation energy level (amount of energy required to initiate a reaction)

45
Q

What does a catalyst do?

A

Alters the rate of a chemical reaction without undergoing any permanent change themselves
They can be used repeatedly and are effective in small amounts

46
Q

What is an active site and how does an enzyme-substrate complex form?

A

An active site is the functional region of an enzyme forming a small hollow/depression
It is lined with R groups which stick off the polypeptide chain and so the substrate can form temporary bonds between the R groups to form an enzyme-substrate complex

47
Q

Why is binding specific?

A

Because the place of the R groups is specific to each enzyme and so a substrate will only fit to the active site of a specific enzyme
This is why enzymes are so specific to the reactions they catalyse

48
Q

What conditions are needed for an enzyme to work? (3)

A
  • must come into physical contact with a substrate
  • must collide with enough energy
  • must have an active site which fits the substrate
49
Q

Describe the earlier lock and key method of enzyme action

A

This model was based on the idea that each substrate has a specific shape that exactly fits the active site of an enzyme (a rigid structure)
This was supported by observations that enzymes are specific in the reactions they catalyse, however a later limitation was discovered - an enzyme’s structure is flexible rather than rigid

50
Q

Describe the induced fit model of enzyme action

A

This model suggests that as the substrate comes into close proximity of the enzyme’s active site, the active changes shape slightly (conformational change) to mould around and bind to the substrate - this is still specific
When the active site changes shape, the enzyme puts a strain on the substrate molecule, which distorts bonds in the substrate and as a result, lowers the activation energy
When the product is formed/leaves, the enzyme resumes its original shape

51
Q

Describe and explain the time vs formation of product/decrease of substrate graph
(beginning, during reaction and end)

A
  • At first, there is a lot of substrate but no product, therefore it is very easy for substrate molecules to come into contact with empty active sites
  • The amount of substrate decreases as it is broken down by the enzyme, resulting in an increase in product
  • As the reaction proceeds, the amount of substrate will continue to decrease and the amount of product will increase
  • This means it becomes more difficult for the substrate to come into contact with empty/free active sites
  • The rate of reaction therefore slows down and the graph will plateau, until the reaction completely stops due to all of the substrate being used up and therefore no new product can be formed
52
Q

How to measure rate of change of a reaction from a graph

A

Work out the gradient of a tangent drawn to the curve at that point (difference in Y over difference in X)

53
Q

Effect of temperature on the rate of enzyme-controlled reactions

A

A rise in temperature increases the kinetic energy of the molecules, resulting in a higher frequency of successful collisions and therefore there is an increased number of enzyme-substrate complexes forming and the rate of reaction increases
Past a certain temperature, bonds in the enzyme begin to break, causing the active site to change shape and eventually denature

54
Q

Effect of pH on the rate of enzyme-controlled reactions

A

Beyond a certain pH either way, the enzyme will denature
Changing the pH will alter the charges on the amino acids/R groups lining the active site, preventing enzyme-substrate complexes from forming

55
Q

Effect of enzyme concentration on the rate of enzyme-controlled reactions

A

As long as there is an excess of substrate, increasing the enzyme concentration will increase the rate of reaction because there are more active sites available for the reaction to occur in - therefore there will be more successful collisions and more ESCs formed
If the substrate concentration was limiting, increasing enzyme concentration any further would have no effect and the graph would level off

56
Q

Effect of substrate concentration on the rate of enzyme-controlled reactions

A

If enzyme concentration is fixed, increasing substrate concentration will increase the rate of reaction as there are more opportunities to fill the active sites
The rate is at its Vmax when all of the enzymes are full and working as fast as they can
After this, the addition of any more substrates will have no effect and the graph will level off

57
Q

How do competitive inhibitors work?

A

These have a similar shape to the substrate, which allows them to bind to and occupy the active site of an enzyme
Binding of a competitive inhibitor to an active site is non permanent and so when it leaves, another molecule can enter

58
Q

How do non-competitive inhibitors work?

A

These inhibitors bind to a site on the enzyme that is not the active site (allosteric site)
Binding of this inhibitor causes a shape change in the enzyme and its active site, meaning the substrate can no longer bind and therefore the enzyme cannot function
This effectively denatures the enzyme and it is mainly irreversible, however there are some exceptions

Biology (4 decks)

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