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A Level Biology > Biological Molecules > Flashcards

Biological Molecules Flashcards

1
Q

Covalent bond

A

A shared pair of electrons between atoms is called a covalent bond
- carbon forms 4 covalent bonds

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2
Q

Which of these is not a polymer:
A- Carbohydrate
B- Protein
C- Lipid
D- Nucleic acid

A

C- lipid
Because while they are made of lots of smaller molecules, they are very different to each other

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3
Q

Monomer and polymer: carbohydrates

A

Monomer
Monosaccharides- glucose (sugars)

Polymer
Polysaccharides- starch, cellulose, glycogen

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4
Q

Monomer and polymer: proteins

A

Monomer
Amino acids

Polymer
Polypeptides & proteins

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5
Q

Monomers and polymers: Nucleic acids

A

Monomer
Nucleotides

Polymer
DNA & RNA

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6
Q

Condensation reaction

A

Joins molecules together

  • a water molecule is released
  • a covalent bond is formed
  • a larger molecule is formed
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7
Q

Hydrolysis reaction

A

Splitting molecules apart

  • water molecule is used
  • covalent bond is broken
  • smaller molecule is formed
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8
Q

Hydrogen bonds

A

Form when a slightly positive and negative charge come close
- weak bonds and easily broken
- represented as a dashed line

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9
Q

General formula for carbohydrate

A

Cn(H2O)n

  • always 2 more hydrogen
  • usually same C and O
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10
Q

Simple sugars/monosaccharides properties

A
  • contains 3-6 carbons
  • soluble in water
  • sweet tasting
  • form crystals
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11
Q

Most common sugar:
- Triose sugar (3)
- Pentose sugar (5)
- Hexose sugar (6)

A

Hexose sugar (6 carbon monosaccharide)

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12
Q

What is the bond between monosaccharides called

A

Glycosidic bond

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13
Q

Alpha glucose

A

OH below
(Google picture :))

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14
Q

Beta glucose

A

OH above

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15
Q

Maltose

A

Glucose + glucose

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16
Q

Sucrose

A

Glucose + fructose

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17
Q

Lactose

A

Glucose + galactose

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18
Q

Glycosidic bonds in: maltose, lactose, sucrose

A

Maltose= alpha 1,4 glycosidic bonds

Lactose= beta 1,4 glycosidic bonds

Sucrose= alpha 1,2 glycosidic bonds

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19
Q

Starch: Amylose

A
  • unbranched
  • compact
  • insoluble

iodine makes it go from orange to blue-black

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20
Q

Starch: amylopectin

A

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

  • highly branched - can be hydrolysed quickly
  • 1,4 bonds between monomers, and 1,6 bonds at branch
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21
Q

What 2 molecules make up starch

A
  • amylose
  • amylopectin
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22
Q

Glycogen

A

Energy store in animals
- alpha glucose
- highly branched - easily hydrolysed
- very compact - good storage molecule
- 1,4 and 1,6 glycosidic bonds
- insoluble in water - do not reduce WP of cells

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23
Q

Cellulose

A

Polysaccharide found in plants
- main structural component of cell walls
- beta glucose
- joined together by 1,4 glycosidic bonds
- each molecule rotated 180° to each other
- high tensile strength due to many hydrogen bonds that form between the long chains of beta glucose molecules

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24
Q

What is the main component of cell walls in bacteria

A

Peptidoglycan

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25
Q

What molecule is found in the exoskeleton of insects

A

Chitin

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26
Q

Reducing sugar

A

One that reduces another compound and is oxidised

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27
Q

Non reducing sugar

A

Can’t donate electrons and cannot be oxidised

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28
Q

What are some reducing sugars

A
  • All monosaccharides
  • some disaccharides

E.g. glucose, fructose, ribose, maltose

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29
Q

What is not a reducing sugar

A

SUCROSE

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30
Q

Benedict’s test for reducing sugars

A
  1. Sample is placed in boiling tube. For a solid, grind/blend and place in water
  2. Add an equal volume of Benedict’s reagent
  3. Heat the mixture gently in a water bath for 5 minutes

Positive result- orange/red

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31
Q

Benedict’s test for non reducing sugars

A
  1. Negative test for reducing sugars
  2. Prepare a fresh sample with water
  3. Add acid
  4. Boil
  5. Add alkali (to neutralise the acid)
  6. Add Benedict’s reagent
  7. Heat

Positive result- orange/red

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32
Q

Colorimeters

A

An instrument that beams a specific wavelength of light through a sample and measures how much of this light is absorbed

Can measure:
- absorbance (how much light is absorbed)
- transmission (how much light is transmitted)

Must be calibrated before taking measurements
- blank placed into colorimeter- should read as 0 as no light absorbed

Results then used to plot a calibration/standard curve

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33
Q

Serial dilution

A

Created by taking a series of dilutions off a stock solution. The concentration decreases by the same quantity between each test tube

Comparison can be:
- visual
- measured through calibration curve
- measures using a colorimeter

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34
Q

Why is water important

A

• component of living organisms
• Cooling function
• Habitat
• Transport systems
• Reactant e.g. photosynthesis
• Photosynthesis

35
Q

Structure of water

A

2 hydrogen ions (+) and 1 oxygen (-)

36
Q

Why is water a good solvent

A
  • Polarity
  • Hydrogen bonding
  • Bond angle
37
Q

Polar & non polar

A

Polar- will dissolve
Non polar- won’t dissolve

38
Q

Polarity

A
  • Each hydrogen atom shares its electron with the atom of oxygen
  • Because the oxygen atom has more protons than hydrogen atoms, it pulls more strongly on these free electrons
39
Q

Hydrogen bonding

A

• when water molecules get closer together, the oppositely charged parts of the molecule attract each other, forming hydrogen bonds
• We call this cohesion
• At room temperature, water forms a lattice

40
Q

Cohesion between water molecules

A
  • at air water surface, cohesion produces surface tension
  • within a column of water, cohesion explains why the column doesn’t break
    E.g. xylem during transpiration
41
Q

Properties of water

A
  • universal solvent
  • liquid at room temperature
  • specific heat capacity
  • latent heat of vaporisation
  • latent heat of fusion
  • density
  • capillarity / cohesion
  • surface tension
42
Q

Universal solvent

A

Because it has polar molecules, water is attracted to any substance that is also polar substances that can become part of water hydrogen bonded structure and will dissolve (hydrophilic)

Triglycerides and large polymers won’t dissolve
(Also non polar)

43
Q

Liquid at room temperature

A

Helps cells transport and use substances like oxygen or nutrients

44
Q

Specific heat capacity

A

Lots of energy needed to change the temperature of water

  • therefore environment outside of organisms resist temperature changes that could cause it damage e.g. lake
45
Q

Latent heat of fusion

A

High latent heat of fusion prevents the liquid environment of cells from freezing and tearing the cells apart, as liquid water temperatures can drop to around -10°C before it begins to freeze

46
Q

Latent heat of vaporisation

A

Lots of energy is needed to evaporate
- it draws the thermal energy from the surface, cooling it as the water evaporates from it (e.g. sweating)

47
Q

Density

A
  • density decreases when freezing as molecules spread out
  • ice forms on the surface of water which means that organisms can live below
  • ice insulates the water below, meaning aquatic organisms don’t freeze and can move around
48
Q

Capillarity/cohesion

A

• adhesion makes water stick to other polar substances, effectively making it ‘wet’
• Upward movement in xylem of tall plants, such as trees, against gravity
• Also important is waters transparency
• Water being transparent and colourless transmits sunlight, enabling aquatic plants to photosynthesise, and enabling us to see, as our eyes are coated in water

49
Q

Surface tension

A

pond skaters and other in class ‘insecta’ are able to glide on surface of ponds
• Water moves up xylem tissue without breaking apart

50
Q

Basic structure of amino acid

A

Amine group
Carboxyl group

H. H. =O
N ———C ——— C
H. R. -OH

51
Q

Elastin

A

Cross linking and coiling for strength
- skin, lungs, bladder, blood vessels

52
Q

Pepsin

A

Single polypeptide chain, 327 amino acids
- symmetrical tertiary structure
- mainly acidic R groups (stable)

53
Q

Conjugated protein

A

One with a prosthetic group (non protein component)

54
Q

Function of proteins

A

• structural- muscle, bone
• Carrier and channel proteins
• All enzymes
• Many hormones
• Antibodies

55
Q

Fibrous proteins

A

• Structural role
• relatively long and thin
• Insoluble in water
• Metabolically inactive

E.g. collagen, keratin, elastin

56
Q

Globular proteins

A

• Metabolic role
• relatively spherical in shape
• Interact with water
E.g. haemoglobin, insulin, pepsin

57
Q

Collagen

A

Structural role
- fibrous protein
- high tensile strength
- not elastic
- flexible
- insoluble

58
Q

Haemoglobin

A
  • Globular protein
  • soluble
  • has a haem group
  • metabolic role
59
Q

Primary structure

A
  • sequence of amino acids bonded by covalent peptide bonds
  • specific for each protein

Only peptide bonds

60
Q

Secondary structure

A
  • occurs when the negatively charged nitrogen and oxygen atoms interact with positively charged hydrogen atoms to form hydrogen bonds

2 shapes can form:
- alpha helix- Occurs when hydrogen bonds form between every fourth peptide bond
- beta pleated sheets- forms when the protein folds so that 2 parts of the polypeptide chain are parallel to each other

Most fibrous proteins have secondary structures e.g. collagen, keratin

Has peptide and hydrogen bonds

61
Q

Tertiary structure

A

Further conformational change of secondary structure leads to additional bonds forming between the R groups
- Tertiary structure determines function

The additional bonds are:
- Hydrogen
- Disulfide
- ionic
- weak hydrophobic interactions

Most common is globular proteins

62
Q

Quaternary structure

A

Exists in proteins that have more than one polypeptide chain working together as a functional macromolecule e.g. haemoglobin

  • each polypeptide chain in the quaternary structure is referred to as a subunit of the protein
63
Q

Lipids

A
  • fats solid at room temp
  • oils liquid at room temp
  • insoluble

Triglycerides, phospholipids, sterols

64
Q

What so lipids dissolve in

A

Organic solvents e.g. alcohol
Do not dissolve in water

65
Q

Role of lipids in organisms

A

• solvent
• Storage
• Thermal insulator
• Energy source
• Waxy cuticle of leaves- prevent it drying out
• Myelin sheath of neurones- electrical insulation
• Phospholipid bilayers
• Stored as adipose tissue in cells
• Organ cushioning

66
Q

Triglycerides

A
  • non polar, hydrophobic molecules
  • made of glycerol and 3 fatty acids
67
Q

Fatty acid

A

A molecule with a hydrocarbon chain and carboxylic acid (contains carboxyl group (COOH)

Shorthand chemical formula for fatty acid is RCOOH

68
Q

Ester bond

A

the bond formed when an organic acid such as a fatty acid joined to an alcohol such as glycerol by a condensation reaction (a triglyceride with 3 fatty acids joined to a glycerol has 3 ester bonds)

69
Q

Saturated and unsaturated fatty acid

A

Saturated
Have no double bonds between carbons

Unsaturated
At least one double bond between carbons

Monounsaturated: one double carbon bond along the molecule
Polyunsaturated: multiple double carbon bonds along the molecule

Presence of a double bond causes kinks/bends - can’t be closely packed making them liquid at room temp.

70
Q

Triglycerides vs phospholipids

A

Similarities
• both contain a glycerol base
• Both contain fatty acid
• Both lipids
• Both have ester binds holding fatty acids to glycerol

Differences
• phospholipid has 2 fatty acids whereas triglyceride has 3
• Phospholipid has one phosphate ion bonded to the glycerol

71
Q

Phospholipids

A

Phosphate head is polar- soluble in water (hydrophilic)

Fatty acid tails are non polar and therefore insoluble in water (hydrophobic)

Phosphate— glycerol — 2 fatty acids

72
Q

Sterols

A

Lipid structure (not fat or oil)
- manufactured in liver and intestines
-i increases membrane stability
- regulation - fluid at low temperatures and stops them becoming too fluid at high temperatures

73
Q

Importance of sterols

A
  • cholesterol
  • vitamin D
  • steroid hormones
  • bile
74
Q

Why is data and nutritional studies often flawed

A

• people digest and metabolise food differently and usually they don’t study the long term impacts
• People have different diets
• Who’s done the study, are they biased e.g. only looking for results to back up what they want
• May only study one group of people e.g. kids

75
Q

Emulsion test- lipids

A
  1. Add 2cm3 of food sample to test tube and grind sample if solid
  2. Add 5cm3 of ethanol
  3. Add 5cm3 of water and shake

Positive = cloudy emulsion
Negative = clear

76
Q

Biuret test- proteins

A
  1. Add food sample to test tube
  2. Add Biuret solution (sodium hydroxide + copper surface)

Positive = purple
Negative = blue

77
Q

Thin layer chromatography (TLC)

A

Technique to analyse small samples via separation
- speed depends on solubility and polarity
- use UV light to see dots that are white/transparent

non polar will travel quickly
polar will stick to surface and travel slowly

78
Q

Stationary phase

A

Not moving

  • thin metal sheet coated in silica or alumina
  • molecules stick to the surface
79
Q

Mobile phase

A

Moving
- flows over the stationary phase
- polar solvents: water, alcohol
- non polar solvents: alkanes

80
Q

Rf value

A

Distance travelled by pigment divided by the disatnce travelled by the solvent

distance traveled by solute
Distance traveled by solvent

81
Q

Ways to see the chromatogram

A

Ninhydrin
- used to see amino acids
-see as brown or purple spots

UV light

Iodine
- enclose the plate with a few iodine crystals
- iodine forms a gas which binds to the molecules in each of the spots

82
Q

Advantages of TLC

A

• The mobile phase moves more quickly through the stationary phase
• The mobile phase moves more evenly through the stationary phase
• There are a range of absorbencies for the stationary phase
• Show a greater separation of components in the mixture

83
Q

Elements of carbohydrate, lipids, proteins, nucleic acids

A

Carbohydrates + lipids =C,H,O
Amino acids= C, H, O, N
Nucleic acids= C, H, O, N, S

A Level Biology (26 decks)

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