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AS biology unit 1 > molecules > Flashcards

molecules Flashcards

1
Q

what is the importance of water as a solvent?

A
  1. The majority of the cell’s reactions take place
    in aqueous solutions e.g cytoplasm.
  2. Water’s solvent properties also mean
    that it acts as a transport medium, as in
    the blood plasma, urine, xylem and
    phloem vessels.
  3. Has different effects on hydrophilic (‘water
    loving’) and hydrophobic (‘water hating’)
    molecules. E.g lipids are hydrophobic (non-
    polar) and do not dissolve in water
  4. Has an important role in temperature
    regulation since evaporation of water from
    a surface cools it down
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2
Q

explain how water acts as a solvent

A

Water molecules are polar (charged) and so form
clusters around ions, glucose and amino acids
separating them in solution

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3
Q

what type of molecules will not dissolve in water?

A

non-polar molecules (hydrophobic) e.g lipids will
not dissolve in water

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4
Q

define the term buffer

A

chemicals
that resist changes in pH and ensure that a
particular environment maintains a particular
pH

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5
Q

give 2 examples of a buffer

A
  1. hydrogencarbonate ions
    2.blood proteins e.g. albumin (the presence of dissolved
    albumin stops too much water leaving the blood through
    the capillaries by osmosis - regulates water potential).
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6
Q

explain the difference of the role of an acidic vs alkaline buffer

A

A buffer can act as both a base and an acid:
• Act as bases by mopping up hydrogen ions to help
neutralise an acidic solution.
• Act as acids by donating hydrogen ions to help
neutralise an alkali solution.

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7
Q

function of potassium

A

Is important in maintaining electrical gradients across neurones.

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8
Q

functions of calcium

A
  1. Calcium pectate is an essential component of the middle lamella of
    plant cell walls.
  2. Calcium is an essential component of bones and teeth in animals
  3. Calcium is essential in blood clotting and muscle contraction in
    animals.
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9
Q

function of magnesium

A

. Essential in giving chlorophyll its light absorbing properties.

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10
Q

functions of iron

A
  1. Is part of the haem group in haemoglobin
  2. Important constituent of electron carriers in respiration.
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11
Q

function of nitrate

A

Is a component of amino acids, nucleic acids and chlorophyll.

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12
Q

functions of phosphate

A
  1. As phospholipids, phosphate is an important component of cell
    membranes.
  2. It is also a major component of other important biological molecules
    including ATP and nucleic acids (DNA).
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13
Q

function of hydrogen carbonate

A

Important as a natural buffer

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14
Q

define macromolecules

A

large molecules e.g sucrose, maltose,
starch, cellulose, glycogen, proteins, triglycerides (lipid),
phospholipids and nucleic acids

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15
Q

define polymers

A

A large molecule formed of repeating similar
subunits (monomers) – joins by polymerisation

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16
Q

what 3 elements do carbohydrates contain

A

• Carbon
• Hydrogen
• Oxygen

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17
Q

general formula of carbohydrates

A

(CH2O)n.

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18
Q

what are monosaccharides

A

are the basic carbohydrate monomers i.e single (simple) sugars.

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19
Q

what are disaccharides?

A

are DOUBLE sugars formed form 2 monosaccharides monomers in a condensation reaction

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20
Q

what are polysaccharides?

A

are complex molecules usually containing of MANY monosaccharide monomers formed in condensation reactions

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21
Q

why is glucose an important monosaccharide

A

All green leaves make glucose using light energy (photosynthesis).

Our bodies transport glucose in the blood as all cells use it in respiration to release energy (produce ATP) – so are important ENERGY stores in living organisms (‘blood sugar’)

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22
Q

define the term isomer

A

the same molecular
formula but different structural formula

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23
Q

what is the difference between a- glucose and b- glucose

A

a- glucose is the basic subunit of complex polysaccharides such as starch and glycogen,
• b- glucose (different functional properties to a- glucose) is the constituent monomer of cellulose

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24
Q

describe formation of disaccharides

A

The chemical reaction when this happens is called a condensation reaction – one molecule of water is lost
This is a reversible reaction as a disaccharide molecule can be broken down into its constituent monosaccharide monomers in a hydrolysis reaction – one molecule of water is gained. (Hydrolysis reaction is important in the digestion of food)

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25
Q

what is the bond formed in condensation reaction of carbohydrates called?

A

glycosidic bond

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26
Q

what is general formula of disaccharides

A

All disaccharides have the general formula
C12H22O11.

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27
Q

name the important disaccharides and how they are formed

A

• Maltose – formed when two a- glucose molecules are linked through a condensation reaction
maltose is formed when starch is digested and requires further digestion to form monomer glucose
• Sucrose – formed when an a- glucose molecule condenses with a fructose molecule
sucrose is the form in which carbohydrates are transported in phloem of plants
• (Lactose – formed when an a- glucose molecule condenses with a galactose molecule)

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28
Q

why is starch such a good storage molecule?

A

• The molecules of both amylose and amylopectin are very COMPACT (aided by the coiled configuration) and, therefore, they contain a rich store of glucose in a small space.
• As it is INSOLUBLE, it will not affect the water relations of the cell – if significant quantities of carbohydrate were stored as glucose this would cause a lot of water to enter by osmosis.
• Being a LARGE MOLECULE it can be retained in the cell and will not easily pass through the cell membrane.
• The BRANCHING nature of amylopectin creates MANY TERMINAL ENDS that are EASILY HYDROLYSED. This aids in the rapid enzymatic breakdown of starch into its constituent glucose molecules at time of high respiratory demand.

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29
Q

the dlipping of 2 adjacent monomers have 2 effects, what are they?

A
  1. The unbranched chains are straighter, as the bulky –CH2OH side groups alternate between being above and below the chain.
  2. Hydrogen bonds can form cross-linkages between adjacent chains (due to the oxygen and the side groups being available on both sides of the chain following the inversion of alternate β- glucose molecules).
30
Q

how is high tensile strength created in cellulose?

A

The cellulose chains (molecules) are grouped together in microfibrils, with each microfibril consisting of many cellulose molecules. Plant cell walls are formed of the cellulose microfibrils orientated into many planes in a lattice structure to further increase its tensile strength.

31
Q

lipids contain what 3 elements?

A

carbon, hydrogen and oxygen

32
Q

describe properties of lipids

A

• Lipids are macromolecules but are not
polymers.
• Lipids are insoluble in water, they are
hydrophobic molecules but are soluble in
organic solvents e.g. ethanol and ether.

33
Q

why are triglycerides hydrophobic?

A

It is because of the long
hydrocarbon tails that triglycerides are
hydrophobic.

34
Q

what are triglycerides made up of?

A

• are made up from 3 fatty acid molecules joined
to a glycerol molecule.

• are formed from 3 condensation reactions
between the fatty acids and the glycerol i.e.
*water is removed.

35
Q

what are bonds formed by condensation reaction of lipids called?

A

ESTER BONDS

36
Q

how can fatty acids vary?

A
  1. The length of the chain, and,
    • 2. Whether there are any double
    bonds present in the hydrocarbon
    chain
37
Q

what is the difference between fats and oils?

A

• Fats are solid (usually animal product) (saturated)
• Oils are liquid (usually plant product) (unsaturated)

38
Q

Triglycerides are macromolecules but
are not polymers. Explain why they are
not polymers

A

A triglyceride is not composed of
repeating sub-units – it has three fatty
acids attached to a glycerol

39
Q

what are the functions of lipids?

A

energy store, thermal insulation, protection, waterproofing (waxy cuticle) and buoyancy

40
Q

what are phospholipids?

A

Phospholipids are similar to triglycerides
but one of the fatty acids molecules is
replaced by a phosphate group (PO4
3-).

41
Q

what are micelles?

A

When phospholipids are mixed with water
they can form surface layers and
spherical structures called micelles

42
Q

Distinguish between a triglyceride and
a phospholipid

A

A triglyceride consists of 3 fatty acids
bonded to a glycerol, while a
phospholipid consists of 2 fatty acids
and a phosphate bonded to a glycerol
i.e one fatty acid is replaced by a
phosphate

43
Q

what elements do proteins contain?

A

C H O N S

44
Q

what are functions of proteins?

A

as enzymes, carrier proteins, antibodies, structural proteins, hormones or contractile proteins

45
Q

how is function of proteins determined?

A

The specific function of a protein depends upon its shape. In turn the shape of the protein is determined by the specific sequence of amino acids in the protein chain.

46
Q

amino acids differ by R groups, what are their effects?

A

Some residues carry a charge and so may be involved in hydrogen bonding, some are hydrophobic
• Influence solubility
• may act as buffers
• Role with forming tertiary structure of proteins
• forming active sites (enzymes)
• interactions with hormones
• forming receptor site

47
Q

what are prions

A

Prions are a particular type of protein found in
mammals and some other animal groups.

48
Q

what is the difference between normal vs disease causing prion?

A

• The secondary structure of normal protein PrP
is composed mainly of a- helixes
• The disease causing form (PrPSc ) has a
higher proportion of beta-sheets (compared to
a helixes)

49
Q

properties of prions

A

Prions are stable, being resistant to extreme temperature and
radiation .

50
Q

3 prion diseases

A

Scrapie that affects sheep
Bovine spongiform encephalopathy (BSE) or’mad
cow disease’ normally cattle are affected through
eating contaminated food products
Variant Creutzfeldt-Jakob disease (vCJD), a human
version of BSE that is normally acquired though eating
contaminated beef products containing the PrPSc
form. Humans lose memory and physical coordination.

51
Q

how can prions arrise

A

spontaneously, by mutations or by eating contaminated food

52
Q

primary structure of proteins

A

The primary structure of a polypeptide(protein) is the sequence of amino acids joined together by peptide bonds in the polypeptide chain.

53
Q

secondary structure a-helix

A

Themostcommonshapesare formed either by coiling to form an a-helix
Hydrogen bonds formed between amino acids at regular intervals)
Thebondstwistthechainof amino acids into a spiral or helical shape.

54
Q

Secondary Structure b - pleated-sheets

A

• Another secondary structure is the folding into b - pleated- sheets
• These are more rigid and less flexible than a-helix
• They are formed by sections of the polypeptide chain
oriented in opposite directions, lying adjacent to each other
• Hydrogen bonds form between the C=O and NH groups

55
Q

tertiary structure

A

This additional folding gives each protein its unique 3D shape and is a consequence of the range of bonds formed between the R-groups of amino acids in the chain.

56
Q

quaternary structure

A

The quaternary structure of a protein arises when two or more polypeptides are bonded together (largely by disulphide bonds), forming a complex, biologically active molecule.

57
Q

conjugated proteins

A

Have a non protein part attached .
• The non protein component is called the
prosthetic group.
• These conjugated proteins include glycoprotein which is important in the cell membrane

58
Q

fibrous protein

A

consistofpolypeptidesarrangedinparallel chains, linked together to form long fibres
- Theparallelchainsarelinkedbycross-bridges to form very strong and stable molecules.
- Theyhaveastructuralfunction
Examples of fibrous proteins are:-
• fibrin - This is a blood protein involved in blood clotting.
• collagen-acomponentofbloodandtendons.
• keratin-foundinhair,hornandnails. .

• E.g. Collagen - a single collagen fibre

59
Q

globular proteins

A

• Otherproteinstakeupatertiarystructurethatis more spherical. These are called globular proteins.
• Theirveryspecific3Dshapeiscrucialtotheir metabolic role
• Mostenzymes,haemoglobinantibodiesand some hormones are globular proteins.

60
Q

Describe the similarities and differences between haemoglobin and collagen

A

Similarities–both are quaternary structures and are found in animals
• Differences–haemoglobin 4 polypeptides, collagen has 3
• 2 types of polypeptide occur in haemoglobin while collagen they are identical
• haemoglobinisglobular,collagenisfibrous

61
Q

what are sub units of nucleic acids

A

The sub unit of nucleic acids is the nucleotide
• Each nucleotide consists of three components
• Pentose sugar (5 carbon) (deoxyribose - DNA, ribose- RNA)
• Phosphate group
• nitrogenous base (always contains nitrogen)

62
Q

how are components combined in nucleotide?

A

•The three components are combined as a consequence of condensation reactions to form the nucleotide.
•Phosphodiester bonds link pentose sugar molecules to phosphate in a nucleic acid strand.

63
Q

what are two types of nucleic acid

A

DNA
RNA

64
Q

describe a molecule of DNA

A

•A molecule of DNA consists of 2 anti-parallel strands with the two strands being held together by hydrogen bonds between adjacent bases

65
Q

what does anti parallel mean

A

Anti-parallel means the two strands a running in opposite directions

66
Q

what is the base pairing rule?

A

•Adenine only pairs with thymine (by 2 hydrogen bonds)
•Guanine only pairs with cytosine (by 3 hydrogen bonds)

67
Q

how is dna arranged?

A

•The DNA molecule is organised as a double helix
•Each strand of the DNA is wound round each other like a twisted ladder, linked together by the bases, following base pairing rules.
•The organization of the DNA is very regular, with there being 10 base pairs for each complete turn of the helix

68
Q

explain semi conservative replication

A
  1. 2.
  2. 4.
    TheenzymeDNAhelicase‘unzips’thetwostrandsoftheDNAbybreakingthe HYDROGEN BONDS between the bases. This allows EACH of the ORIGINAL STRANDS to become a TEMPLATE for the formation of TWO DNA molecules.
    FREE NUCLEOTIDES are linked to the template strands in the correct sequence as a consequence of bases on the ‘free’ nucleotides following BASE PAIRING RULES with the bases on the template strands.
    The nucleotides of each strand are joined together by the enzyme DNA POLYMERASE
    Each of the new DNA molecules contains one original (template) strand and one new DNA strand. This is why the process of DNA replication described is called SEMI- CONSERVATIVE REPLICATION.
69
Q

what is evidence for semi conservative replication

A
  1. THE CONSERVATIVE MODEL – this proposed that the parental DNA remained intact but copied the new DNA molecule (analogous to a photocopier).
  2. THE SEMI-CONSERVATIVE – as described at earlier and in the previous diagram.
    One of the most famous experiments in the history of Biology was carried out by Meselson and Stahl, who proved that the SEMI-CONSERVATIVE model is the process involved.
    Meselson and Stahl cultured the bacterium E.Coli using the ‘heavy’ isotope of Nitrogen, 15N. The 15N was incorporated into the bases of the DNA in all the bacteria over time, as older bacteria (containing the normal 14N) died and were replaced.
    The bacteria were then transferred to a medium containing the lighter (normal) 14N.
70
Q

what were the key stages of Meselson and Stahls experiments

A
  1. Bacteria growing in 14N (before transfer to 15N).
  2. Bacteria growing in 15N (many generations after transfer from 14N)
  3. One generation after transfer to 14N 4. Two generations after transfer to 14N.
71
Q

Explanation of Meselson and Stahl’s results

A

• After one generation – The intermediate position of the DNA can be explained by ALL the DNA consisting of ONE STRAND that has the bases containing 15N and ONE STRAND having bases containing 14N.
• After two generations- About half the DNA consisted of ‘mixed’ DNA of both 14N and 15N but the other half was DNA that only contained 14N.

AS biology unit 1 (5 decks)

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