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Biology Module 2 > Lipids and Proteins > Flashcards

Lipids and Proteins Flashcards

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1
Q

What are lipids?

A
  • contain elements carbon, hydrogen and oxygen
  • non-polar, not soluble in water
  • are macromolecules
  • e.g. triglycerides, phospholipids and sterols
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2
Q

What are macromolecules?

A
  • large complex molecules

- not built from repeating units or monomers like polysaccharides

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3
Q

What makes up a triglyceride?

A
  • 1 glycerol molecule (member of alcohol)

- 3 fatty acids (member of carboxylic acids that contain carboxyl group -COOH, with hydrocarbon chain attached)

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4
Q

How is a triglyceride formed?

A
  • glycerol and fatty acid both contain hydroxyl group
  • OH groups interact
  • leads to formation of 3 water molecules and bonds between molecules called ester bonds
  • reaction is esterification an example of a condensation reaction
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5
Q

How are triglycerides broken down?

A
  • 3 water molecules need to be supplied

- an example of hydrolysis reaction

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6
Q

How do the proportions of oxygen and hydrogen differ in carbohydrates and lipids?

A
  • higher proportion of hydrogen in lipids

- lower proportion of oxygen in lipids

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7
Q

What is the general formula for lipids?

A
  • CH3(CH2)nCOOH
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8
Q

What are phospholipids?

A
  • contain element phosphorus as well as hydrogen, carbon and oxygen
  • inorganic phosphate ions found in cytoplasm
  • phosphate ions have extra electrons, so negatively charged, making them soluble in water
  • one fatty acid chain in triglyceride replaced by phosphate group to make a phospholipid
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9
Q

What is the structure of a phospholipid like?

A
  • fatty acid chains are non-polar tail, repel water are hydrophobic
  • phosphate group is charged head, attract water, hydrophilic
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10
Q

How does a phospholipid interact with water due to the dual hydrophobic/hydrophilic structure?

A
  • form a layer on surface of water
  • phosphate heads in water and fatty acid tails out of the water
  • due to this called surface active agents or surfactants
  • also form bilayer (two-layered sheet formation) with hydrophobic tails toward centre of sheet, protected from water by hydrophilic heads
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11
Q

What role does the bilayer play in a phospholipid?

A
  • key role in forming cell membranes
  • able to separate an aqueous environment in which cells usually exist from the aqueous cytosol within cells
  • thought this is how cells were formed and later how membrane-bound organelles within cells
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12
Q

What are sterols?

A
  • complex alcohol molecules
  • based on a four carbon ring structure with OH group at one end
  • have dual hydrophobic/hydrophilic characteristics
  • OH group polar hydrophilic, rest of molecule is hydrophobic
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13
Q

Cholesterol is a sterol. What’s its role in the body?

A
  • in liver and intestines mostly
  • role in formation of cell membranes, becoming positioned between phospholipids with the OH group at the periphery of the membrane
  • this adds stability to cell membrane and regulates fluidity by keeping membranes at low temperatures and stopping them becoming too fluid at high temperatures
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14
Q

What substances are manufactured using cholesterol?

A
  • Vitamin D
  • steroid hormones
  • bile
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15
Q

What are the roles of lipids due to their non-polar nature?

A
  • membrane formation and creation of hydrophobic barriers
  • hormone production
  • electrical insulation necessary for impulse transmission
  • waterproofing, e.g. birds feathers and on plants leaves
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16
Q

Lipids have important role in long-term energy storage. Where are they stored? What do they provide?

A
  • stored under the skin and around vital organs
    Provide:
  • thermal insulation to reduce heat loss for example in penguins
  • cushioning to protect vital organs like the kidneys and heart
  • buoyancy for aquatic animals like whales
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17
Q

How can lipids be identified?

A
  • emulsion test
  • sample mixed with ethanol
  • then mixed with water and shaken
  • if white emulsion forms as layer on top of the solution it indicates presence of lipid
  • if it remains clear test is negative
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18
Q

What is a saturated lipid?

A
  • fatty acid chains that have no double bonds present between the carbon atoms
  • because all the carbon atoms have maximum number of bonds with hydrogen atoms
  • makes them (solid) fats
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19
Q

What is a unsaturated lipid?

A
  • fatty acid with double bonds between some of the carbon atoms
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20
Q

What is a monounsaturated lipid?

A
  • 1 double bond between carbon atoms
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21
Q

What is a polyunsaturated lipid?

A
  • 2 or more double bonds between carbon atoms
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22
Q

What do the double bonds in a lipid cause?

A
  • causes molecule to kink or bend
  • therefore cannot pack so closely together
  • makes them liquid at room temperature rather than solid
  • described as oils rather than fats
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23
Q

What type of triglyceride does plants contain and how does it affect them?

A
  • unsaturated triglycerides
  • normally occur as oils
  • more healthy in humans than saturated triglycerides
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24
Q

How do phospholipids in membranes of extremophiles withstand extremes of temperature and pH?

A
  • cross links stabilise membrane
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25
Q

How does the emulsion test work for lipids?

A
  • sample/lipid dissolved in ethanol
  • water mixed with ethanol (and lipid) solution
  • water displaces lipid from ethanol forming suspension
  • suspension forms because lipids not soluble in water
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26
Q

What is a peptide?

A
  • polymers made of amino acid molecules
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27
Q

What are proteins?

A
  • one or more polypeptides
  • arranged as complex macromolecules
  • specific biological functions
  • all proteins contain elements carbon, hydrogen, oxygen and nitrogen
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28
Q

What is the structure of an amino acid?

A
  • different R-groups in different amino acids
  • amine group
  • carboxylic acid group
  • 20 different amino acids are commonly found in cells
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29
Q

How are peptides formed?

A
  • amino acids join when H in amine group and OH in carboxylic acid group reacts
  • R-groups not involved at this point
  • peptide bond formed and water produced
  • example of condensation reaction
  • resulting compound is a dipeptide
30
Q

How is a polypeptide formed?

A
  • when many amino acids are joined together by peptide bonds
  • reaction catalysed by the enzyme peptidyl transferase present in ribosomes
31
Q

What do the R-groups in an amino acid do?

A
  • different R-groups interact with each other forming different types of bonds
  • lead to polypeptides folding into complex structures (proteins)
  • Specific shape of the proteins allow for different functions.
32
Q

What is the primary structure of proteins?

A
  • only bonds involved are peptide bonds
  • sequence in which amino acids are joined
  • directed by information carried by DNA
33
Q

How is the secondary structure of proteins formed?

A
  • oxygen, nitrogen and hydrogen atoms of basic, repeating structure of amino acids interact
34
Q

What are the two different types of secondary structure?

A
  • alpha helix

- beta pleated sheets

35
Q

How is the alpha helix secondary structure formed?

A
  • hydrogen bonds may form within the amino acid chain, pulling it into a coil shape called an alpha helix
36
Q

How is the beta pleated sheets secondary structure formed?

A
  • polypeptide chains lie parallel to one another
  • joined by hydrogen bonds, forming sheet like structures
  • pattern formed by individual amino acids cause structure to appear pleated
37
Q

How is the tertiary structure of proteins formed?

A
  • often includes sections of secondary structure
  • coiling or folding of sections of proteins into their secondary structures brings R-groups of different amino acids closer together so they are close enough to interact and further folding of these section occur to form tertiary structures
38
Q

What bonds are present in tertiary structures due to the interactions between the R-groups?

A
  • hydrophobic and hydrophilic interactions, weak interactions between polar and non-polar R-groups
  • hydrogen bonds
  • ionic bonds, form between oppositely charged R-groups
  • disulphide bridges, covalent and only form between R-groups that contain sulfur atoms
39
Q

List bonds involved in protein structures in order of strongest to weakest:

A
  • disulfide bridge
  • ionic bond
  • hydrogen bond
  • hydrophobic/hydrophilic interaction
40
Q

How is a quaternary structure formed?

A
  • results from association of two or more individual proteins called subunits
  • held by same bonds as tertiary structure, but are between different protein molecules rather than within just one
  • protein subunits can be identical or different
41
Q

How does the hydrophobic and hydrophilic interactions affect the protein?

A
  • the proteins are assembled in the aqueous cytoplasm
  • affects how the protein folds
  • hydrophilic R-groups are on outside of the protein
  • hydrophobic R-groups on the inside of the molecule shielded from the water in the cytoplasm
42
Q

How are peptides broken?

A
  • proteases are enzymes that catalyse reverse reaction
  • water molecule used to break peptide bond in hydrolysis reaction
  • reforms amine and carboxylic acid groups
43
Q

What is the biuret test?

A
  • 3cm^3 of liquid sample mixed with an equal volume of 10% sodium hydroxide solution
  • 1% copper sulphate solution added a few drops at a time till solution turns blue
  • solution mixed and left to stand for 5 mins
44
Q

What colour does the solution turn if it contains protein in the biuret test?

A
  • violet
45
Q

What colour would be expected if there was amino acids present and not proteins in the biuret test? Why?

A
  • no peptide bonds present as no protein
  • test is negative, solution remains blue
  • ac copper sulfate solution is blue
46
Q

Why is the biuret test not used quantitatively?

A
  • biuret test identifies peptide bonds
  • degree of colour change is dependent on number of said bonds
  • different proteins have different number of bonds
  • different degrees of colour change could indicate different proteins and not different quantities of protein
47
Q

How do hydrogen bonds form within the secondary structure of proteins?

A
  • oxygen slightly negative and hydrogen slightly positive

- oxygen and hydrogen attract each other

48
Q

Why does alpha keratin (primarily composed of alpha helices) have a more regular structure than the quaternary protein haemoglobin?

A
  • secondary structures are simple, repeating structures
  • globular protein, haemoglobin has a tertiary structure
  • tertiary structure formed from complex folding of secondary structure
49
Q

Compare and contrast the role of R-group interactions in the formation of a tertiary and quaternary structures of proteins

A

Tertiary structure:
- interact within a protein molecule, determines shape of molecule
Quaternary Structure:
- interact between protein molecules, holds molecules together
Both:
- involve same interactions e.g. hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic and hydrophilic interactions

50
Q

How do globular proteins form?

A
  • when proteins fold into their tertiary structure
  • so the hydrophobic R-groups on the amino acids are kept away from the aqueous environment
  • hydrophilic R-groups kept on the outside of the protein
  • means proteins soluble in water
51
Q

What are the roles of globular proteins?

A
  • compact
  • roughly spherical
  • water soluble, important for functions like regulating certain processes e.g. chemical reactions, immunity, muscle contraction and more
52
Q

What is insulin and its roles?

A
  • globular protein
  • hormone involved in regulation of blood glucose concentration
  • hormones transported in bloodstream, so need to be soluble
  • hormones also have to fit into specific receptors on cell-surface membranes to have effect so need precise shape
53
Q

What are conjugated proteins?

A
  • globular proteins
  • contain non-protein component called prosthetic group
  • e.g. haemoglobin and catalase
54
Q

What are proteins called without prosthetic groups?

A
  • simple proteins
55
Q

What are the different types of prosthetic groups?

A
  • lipids or carbohydrates can combine with proteins forming lipoproteins or glycoproteins
  • metal ions and molecules derived from vitamins also form prosthetic groups
  • haem groups, contain iron (Fe^2+)
56
Q

How does haemoglobin’s structure relate to its function?

A
  • quaternary protein
  • made from four polypeptides, two alpha and two beta subunits
  • each subunit contains harm group
  • iron present in each harm group able to combine reversibly with oxygen molecules
  • enables haemoglobin to transport oxygen around the body
57
Q

What is haemoglobin?

A
  • red
  • oxygen carrying
  • found in red blood cells
58
Q

What is catalase?

A
  • enzyme

- catalyse reactions, meaning they increase reaction rates and each enzyme is specific to a particular reaction

59
Q

How does catalase structure relate to its function?

A
  • quaternary protein, contains 4 harm groups
  • presence of iron in harm groups allow catalase to interact with hydrogen peroxide (byproduct of metabolism and damages cells and its components if its allowed to accumulate) and speed up its breakdown
60
Q

How are fibrous proteins formed?

A
  • from long insoluble molecules

- due to presence of high proportion of amino acids with hydrophobic R-groups in their primary structures

61
Q

What do fibrous proteins contain?

A
  • limited range of amino acids

- usually with small R-groups

62
Q

In a fibrous protein the amino acid primary structure is usually quite repetitive. What does this mean?

A
  • very organised structures reflected in roles of fibrous structures
63
Q

What are examples of fibrous proteins?

A
  • Keratin
  • elastin
  • collagen
64
Q

What do fibrous proteins tend to make?

A
  • strong, long molecules

- they’re not folded into complex 3D shapes like globular proteins

65
Q

How does keratin’s structure relate to its role?

A
  • large proportion of sulphur-containing amino acid, cysteine
  • results in many strong disulfide bridges forming strong, inflexible, and insoluble materials
  • more bonds makes it less flexible and vice versa
66
Q

Where is keratin present?

A
  • hair
  • skin
  • nails
67
Q

Where are elastic fibres present, containing elastin?

A
  • walls of blood vessels

- in alveoli of lungs

68
Q

How does elastin’s structure relate to its function?

A
  • quaternary structure
  • made from stretchy molecules called tropoelastin
  • give structures flexibility to expand when needed, but also return to normal size
69
Q

Where is collagen present?

A
  • skin
  • tendons
  • ligaments
  • nervous system
70
Q

How does collagen’s structure relate to its function?

A
  • number of different forms
  • all made of 3 polypeptides wound together in long and strong rope-like structure
  • gives flexibility
71
Q

Describe the differences in properties and functions of hormone insulin and keratin present in hair and nails:

A

Insulin:
- globular protein, soluble, specific shape, binds to receptor, chemical messenger
Keratin:
- fibrous protein, strong, structural function/example (e.g. hair, nails)

72
Q

Why are globular proteins soluble in water but fibrous ones aren’t?

A

globular proteins have hydrophobic R groups in centre and hydrophilic R group on outside
- fibrous proteins have all R groups on outside of molecules

Biology Module 2 (16 decks)

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