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Biology > Module 2.2 - Biological Molecules > Flashcards

Module 2.2 - Biological Molecules Flashcards

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1
Q

Define lipids

A

Dissolve in organic solvents (e.g. alcohol) but not water

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2
Q

Roles of lipids in organisms

A

Thermal insulation
Phospholipids in plasma membrane
Myelin sheath of neurones - electrical insulation
Energy source
Energy store - lipids store in adipose cells
Steroid hormones
Waxy cuticle of leaves - prevents drying out

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3
Q

2 major groups of lipids

A

Glycerolipids (energy store/source)

Glycerophospholipids (phospholipids)

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4
Q

What is a saturated fatty acid?

A

No double bonds in hydrocarbon chain

Raise cholesterol

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5
Q

What is a mono-unsaturated fatty acid?

A

One carbon double bond

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6
Q

What is a poly-unsaturated fatty acid?

A

At least two double bonded carbons

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7
Q

What is an ester bond?

A

A covalent bond between glycerol and fatty acids

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8
Q

When are atoms most stable?

A

When their outer outer energy levels/electron shells are full

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9
Q

Define covalent bond

A

A shared pair of electrons between two atoms

Forms a strong bond

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10
Q

How many covalent bonds can carbon form?

A

4

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11
Q

How are biological molecules grouped?

A

By chemical properties

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12
Q

Are lipids polymers?

A

No because even though they are made of lots of smaller molecules, they are very different to each other

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13
Q

Monomer of carbohydrates

A

Monosaccharides

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14
Q

Polymer of carbohydrates

A

Polysaccharides

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15
Q

Monomer of proteins

A

Amino acids

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16
Q

Polymer of proteins

A

Polypeptides and proteins

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17
Q

Monomer of nucleic acids

A

Nucleotides

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18
Q

Polymer of nucleic acids

A

DNA and RNA

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19
Q

Condensation reactions

A

Link biological monomers together
A water molecule is released
A covalent bond is formed
A larger molecule is formed

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20
Q

Hydrolysis reactions

A

Splits biological molecules apart
A water molecule is used
A covalent bond is broken
Smaller molecules are formed

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21
Q

Points about hydrogen bonds

A

Polymer functions often rely on their shape, and hydrogen bonds often hold them in this shape
Hydrogen bonds form when a slightly positive and slightly negative charge come close
Weak and easily broken
In polymers, thousands are strong enough to keep the shape of the molecule

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22
Q

Points about simple sugars/monosaccharides

A 
Contain 3-6 carbons
Soluble in water
Sweet tasting
Form crystals
Can be grouped based on number of carbons (e.g. triose, pentose, hexose - most common)
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23
Q

Name of covalent bond between monosaccharides

A

Glycosidic bond

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24
Q

Difference between alpha and beta glucose

A

Alpha - H above OH on carbon 1

Beta - OH above H on carbon 1

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25
Q

Three common disaccharides

A

Maltose - 2 alpha glucose
Sucrose - alpha glucose + fructose
Lactose - beta glucose + galactose

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26
Q

Why is beta glucose not used for energy storage?

A

Plant and animals only have enzymes capable of breaking down alpha glucose in respiration, not beta glucose due to the difference in structure
Therefore beta glucose can’t be respired so is not used for energy storage

27
Q

Points about amylose

A

Condensation reaction between two alpha glucose molecules to form maltose repeated thousand of times to form the polysaccharide amylose (controlled by enzymes)
Alpha glucose molecules are held together with a 1, 4 glycosidic bond
Amylose forms a spring shape (held in place by hydrogen bonds) due to the shape of glucose and the glycosidic bonds
Unbranched, compact, insoluble
Iodine can get caught in the spring shape of the amylose, making it go from orange to blue-black

28
Q

Points about amylopectin

A

Branches of alpha glucose chains with 1, 4 glycosidic bonds joined at ends to another chain by a 1, 6 glycosidic bond

29
Q

Points about starch

A

Plant energy storage
Mixture of amylose and amylopectin molecules
Stored in starch grains, chloroplasts and storage organs (grains)
Store of energy because it can be broken down into alpha glucose (for respiration) molecules by enzymes in hydrolysis reactions

30
Q

Points about glycogen

A

Animal energy storage
Polysaccharide of alpha glucose
1, 4 linked chains are shorter and more branched (more 1, 6 bonds) than starch
More branches = more ends to be broken off = faster break down = faster energy release
More compact than starch
Found in glycogen granules in animal cells (e.g. in liver and muscles)

31
Q

Starch and glycogen similarities

A

Insoluble in water so do not reduce water potential of cells

Store glucose molecules in chains so they can easily be ‘broken off’ and the glucose used in respiration

32
Q

Points about cellulose

A

Polysaccharide of thousands of beta glucose molecules formed in a condensation reaction
Forms with 1, 4 glycosidic bonds in a long, straight and unbranched chain
Every beta glucose molecule is flipped 180°from the last to form the glycosidic bond

33
Q

How are cellulose chains arranged to make cells walls?

A

Hydrogen bonds form between OH groups on neighbouring chains and cellulose chains become cross linked to form a microfibril
Microfibrils are held together by more hydrogen bonds to form macrofibrils
Macrofibrils are embedded in pectin (polysaccharide) which glues them together in a criss cross structure (held in place by H bonds) to form cell walls
Criss cross structure allows water to pass through easily but because macrofibrils are very strong, water moving into plant cells does not cause them to burst
Wall prevents bursting and in turgid cells helps to support the whole plant

34
Q

Other carbohydrate polymers used in other organisms

A

Peptidoglycan (murein) - bacterial cell walls

Chitin - exoskeleton of insects

35
Q

Functions of proteins

A 
Structural - muscle and bone
Carrier and channel proteins
Enzymes
Many hormones 
Antibodies
Crucial for growth and repair and metabolic activity
36
Q

Points about amino acids

A

20 different amino acids - each has a different R group
Different R groups have different properties (small/large, hydrophobic/hydrophilic, opposite charges)
Monomers of proteins
Joined by a condensation reaction

37
Q

Covalent bond between amino acids

A

Peptide bond

38
Q

Name for 2 amino acids joined

A

Dipeptide

39
Q

Difference between making proteins in plants and animals

A

Plants make their own (if nitrates are in the soil)
Animals need proteins in their diets - broken into amino acids in digestion and built back up to make proteins for the body

40
Q

What is transcription?

A

Taking the message from the original DNA code and making a copy into messenger RNA (mRNA)

41
Q

What is translation?

A

Taking the message from mRNA and translating it into a chain of amino acids to make a protein

42
Q

5 steps of transcription

A

1) DNA helicase unwinds the double helix of DNA
2) The two strands of DNA are separated so free nucleotides in the cytoplasm can fit in
3) Free nucleotide bases attach to the DNA by their complementary base pair rules (thymine is replaced by uracil) to form mRNA
4) The single mRNA strand moves away from the DNA helix and another enzyme zips the two strands of DNA back together
5) The single mRNA strand is small enough to leave the nucleus through a nuclear pore and enter the cytoplasm

43
Q

5 steps of translation

A

1) The mRNA enters the ribosome
2) tRNA (transfer RNA) enters the ribosome and brings a specific amino acid with it that corresponds to the codon on the mRNA strand (3 bases)
3) The tRNA has an anti-codon that matches the mRNA codon so they pair together using complementary base rules
4) The amino acid brought by the first tRNA is attached to the second amino acid by a peptide bond
5) When all the code has been read and amino acids joined together, the mRNA leaves the ribosome and a new protein has been made

44
Q

Points about the primary structure of proteins

A

The primary structure is every single different protein in an organism having a unique sequence of amino acids
This determines its structure, which in turn determines its properties and function

45
Q

Points about protease

A

Enzymes that break down peptide bonds
Used in digestion
Used to break down hormones so their effect isn’t constant

46
Q

Points about secondary structure

A

Polypeptides are stabilised as they’re formed to stop them tangling/breaking by being coiled (alpha helix) or pleated (beta pleated sheet)
Held in place by hydrogen bonds
Combined strength of lots of hydrogen bonds gives stability

47
Q

Why is the secondary structure of a protein dependent on the primary structure?

A

The primary structure is the unique sequence of amino acids in the protein
Different proteins have different combinations of amino acids which each have different R groups with different properties
These different properties mean that hydrogen bonds form in different places in the coils/pleats meaning some are more/less coiled/pleated than others

48
Q

Points about the tertiary structure

A

Overall 3D structure of the protein
Coil/pleat coils or folds into final shape
Key to protein’s function

49
Q

Bonds that maintain protein tertiary structures

A

Disulphide bonds
Ionic bonds
Hydrogen bonds
Hydrophobic/hydrophilic interactions

50
Q

Points about disulphide bonds in a protein’s tertiary structure

A

The amino acid cysteine contains sulphur

Where two cysteines are found close to each other a covalent bond can form

51
Q

Points about ionic bonds in a protein’s tertiary structure

A

R groups sometimes carry a charge, either positive or negative
Where oppositely charged amino acids are found close to each other an ionic bond forms

52
Q

Points about hydrogen bonds in a protein’s secondary/tertiary structure

A

Wherever slightly positively charged groups are found close to slightly negatively charged groups hydrogen bonds form

53
Q

Points about hydrophilic/hydrophobic interactions in a protein’s tertiary structure

A

In a water-based environment, hydrophobic amino acids will be most stable if they are held together with water excluded
Hydrophilic amino acids tend to be found on the outside in globular proteins, with hydrophobic amino acids in the centre

54
Q

Points about globular proteins

A

Spherical
Soluble - hydrophilic groups on outside
Metabolic
E.g. enzymes, plasma proteins, antibodies, haemoglobin

55
Q

Points about fibrous proteins

A

Fibres
Insoluble
Structural
E.g. collagen, keratin

56
Q

Points about haemoglobin

A 
Globular protein
Quaternary structure (range of amino acids -> mostly alpha helices -> alpha and beta chains -> 2 alpha and 2 beta chains)
57
Q

Points about collagen

A

Fibrous protein
Quaternary structure - 3 polypeptide chains tightly wound around each other, hydrogen bonds between them gives the molecule strength
Every 3rd amino acid on each polypeptide chain is a glycine, which are small and allow close packing
Covalent bonds crosslink parallel collagen molecules, forming a collagen fibril
The ends of molecules and covalent bonds are staggered to add strength
Many fibrils form a collagen fibre

58
Q

Functions of collagen

A

Lines arterial walls - prevents blood at high pressure bursting walls
Tendons - all muscles to pull bone for movement
Bones - collagen reinforced with other materials to make them hard
Cartilage and connective tissue
Cosmetic treatments - collagen injections can make lips look fuller

59
Q

Collagen and cellulose similarities

A

Both structural polymers

Both insoluble in water

60
Q

Collagen and cellulose differences

A

Cellulose is a polysaccharide, collagen is a polypeptide

Cellulose is only found in plants, collagen is not found in plants

61
Q

Chemical elements that make up biological molecules

A

C, H and O for carbohydrates
C, H and O for lipids
C, H, O, N and S for proteins
C, H, O, N and P for nucleic acids

62
Q

Points about triglycerides

A

3 fatty acids join with ester bond to a glycerol molecule in a condensation reaction
Ester bonds form at the 3 OH groups on the glycerol (3 water molecules also released)
Insoluble in water - hydrophobic as charges are evenly distributed on molecule
Soluble in organic solvents

63
Q

Points about phospholipids

A

2 fatty acids joined with an ester bond to a phosphate group and a glycerol molecule
Soluble head (hydrophilic), insoluble tails (hydrophobic) in water
Soluble in organic solvents
Involved in cell membranes

64
Q

Points about cholesterol

A

Made from 4 carbon rings
Hydrophobic - insoluble in water
Soluble in organic solvents
Involved in cell membranes

Biology (22 decks)

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