Module 2.2 - Biological Molecules Flashcards
1
Q
Define lipids
A
Dissolve in organic solvents (e.g. alcohol) but not water
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
3
Q
2 major groups of lipids
A
Glycerolipids (energy store/source)
Glycerophospholipids (phospholipids)
4
Q
What is a saturated fatty acid?
A
No double bonds in hydrocarbon chain
Raise cholesterol
5
Q
What is a mono-unsaturated fatty acid?
A
One carbon double bond
6
Q
What is a poly-unsaturated fatty acid?
A
At least two double bonded carbons
7
Q
What is an ester bond?
A
A covalent bond between glycerol and fatty acids
8
Q
When are atoms most stable?
A
When their outer outer energy levels/electron shells are full
9
Q
Define covalent bond
A
A shared pair of electrons between two atoms
Forms a strong bond
10
Q
How many covalent bonds can carbon form?
A
4
11
Q
How are biological molecules grouped?
A
By chemical properties
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
13
Q
Monomer of carbohydrates
A
Monosaccharides
14
Q
Polymer of carbohydrates
A
Polysaccharides
15
Q
Monomer of proteins
A
Amino acids
16
Q
Polymer of proteins
A
Polypeptides and proteins
17
Q
Monomer of nucleic acids
A
Nucleotides
18
Q
Polymer of nucleic acids
A
DNA and RNA
19
Q
Condensation reactions
A
Link biological monomers together
A water molecule is released
A covalent bond is formed
A larger molecule is formed
20
Q
Hydrolysis reactions
A
Splits biological molecules apart
A water molecule is used
A covalent bond is broken
Smaller molecules are formed
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
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)
23
Q
Name of covalent bond between monosaccharides
A
Glycosidic bond
24
Q
Difference between alpha and beta glucose
A
Alpha - H above OH on carbon 1
Beta - OH above H on carbon 1
25
Three common disaccharides
Maltose - 2 alpha glucose
Sucrose - alpha glucose + fructose
Lactose - beta glucose + galactose
26
Why is beta glucose not used for energy storage?
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
Points about amylose
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
Points about amylopectin
Branches of alpha glucose chains with 1, 4 glycosidic bonds joined at ends to another chain by a 1, 6 glycosidic bond
29
Points about starch
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
Points about glycogen
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
Starch and glycogen similarities
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
Points about cellulose
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
How are cellulose chains arranged to make cells walls?
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
Other carbohydrate polymers used in other organisms
Peptidoglycan (murein) - bacterial cell walls
| Chitin - exoskeleton of insects
35
Functions of proteins
```
Structural - muscle and bone
Carrier and channel proteins
Enzymes
Many hormones
Antibodies
Crucial for growth and repair and metabolic activity
```
36
Points about amino acids
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
Covalent bond between amino acids
Peptide bond
38
Name for 2 amino acids joined
Dipeptide
39
Difference between making proteins in plants and animals
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
What is transcription?
Taking the message from the original DNA code and making a copy into messenger RNA (mRNA)
41
What is translation?
Taking the message from mRNA and translating it into a chain of amino acids to make a protein
42
5 steps of transcription
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
5 steps of translation
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
Points about the primary structure of proteins
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
Points about protease
Enzymes that break down peptide bonds
Used in digestion
Used to break down hormones so their effect isn’t constant
46
Points about secondary structure
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
Why is the secondary structure of a protein dependent on the primary structure?
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
Points about the tertiary structure
Overall 3D structure of the protein
Coil/pleat coils or folds into final shape
Key to protein’s function
49
Bonds that maintain protein tertiary structures
Disulphide bonds
Ionic bonds
Hydrogen bonds
Hydrophobic/hydrophilic interactions
50
Points about disulphide bonds in a protein’s tertiary structure
The amino acid cysteine contains sulphur
| Where two cysteines are found close to each other a covalent bond can form
51
Points about ionic bonds in a protein’s tertiary structure
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
Points about hydrogen bonds in a protein’s secondary/tertiary structure
Wherever slightly positively charged groups are found close to slightly negatively charged groups hydrogen bonds form
53
Points about hydrophilic/hydrophobic interactions in a protein’s tertiary structure
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
Points about globular proteins
Spherical
Soluble - hydrophilic groups on outside
Metabolic
E.g. enzymes, plasma proteins, antibodies, haemoglobin
55
Points about fibrous proteins
Fibres
Insoluble
Structural
E.g. collagen, keratin
56
Points about haemoglobin
```
Globular protein
Quaternary structure (range of amino acids -> mostly alpha helices -> alpha and beta chains -> 2 alpha and 2 beta chains)
```
57
Points about collagen
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
Functions of collagen
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
Collagen and cellulose similarities
Both structural polymers
| Both insoluble in water
60
Collagen and cellulose differences
Cellulose is a polysaccharide, collagen is a polypeptide
| Cellulose is only found in plants, collagen is not found in plants
61
Chemical elements that make up biological molecules
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
Points about triglycerides
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
Points about phospholipids
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
Points about cholesterol
Made from 4 carbon rings
Hydrophobic - insoluble in water
Soluble in organic solvents
Involved in cell membranes
