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A level Biology > Biological molecules > Flashcards

Biological molecules Flashcards

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1
Q

Why does water have a high boiling point?

A

This is because of the hydrogen bonding between water molecules. it takes a lot of energy to increase the temperature of water and cause water to become gaseous.

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2
Q

Why is water less dense as a solid?

A

As water is cooled the hydrogen bonds fix the positions of the polar molecules slightly further apart than the average distance in the liquid state. this produces a giant, rigid but open structure, resulting in a solid that is less dense than liquid water.

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3
Q

Cohesion in water

A

Water has cohesive properties. it moves as one mass because the molecules are attracted to each other (cohesion).

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4
Q

Adhesion in water

A

Water has adhesive properties - this is where water molecules are attracted to other materials.

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5
Q

Surface tension in water

A

Water molecules are more strongly cohesive to each other than they are to air, this results in water having a ‘skin’ of surface tension

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6
Q

Why is water important for life?

A
  • acts as a solvent in which many of the solutes in an organism can be dissolved
  • water makes a very efficient transport medium within living things
  • water acts as a coolant
  • water is a constant environment
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7
Q

what are the only elements carbohydrates contain?

A

Carbon, Hydrogen and Oxygen

CHO

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8
Q

what is a single sugar unit known as?

A

A monosaccharide. examples include glucose, fructose and ribose

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9
Q

what do 2 monosaccharides form when they’re linked together?

A

A disaccharide, for example lactose and sucrose

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10
Q

what do 2 or more monosaccharides form?

A

A polymer called a polysaccharide. Examples include glycogen, cellulose and starch

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11
Q

what is the formula of glucose?

A

glucose molecules have the chemical formula C6H12O6.

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12
Q

What type of monosaccharide is glucose?

A

glucose is a monosaccharide composed of 6 carbons and therefore is a hexose monosaccharide

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13
Q

Structure of glucose?

A

there are 2 structural variations of the glucose molecule, alpha and beta glucose.

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14
Q

solubility of glucose

A

glucose molecules are polar and soluble in water. this is due to the hydrogen bonds that form between the hydroxyl groups and water molecules. this solubility in water is important, because it means glucose is dissolved in the cytosol of the cell.

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15
Q

what happens in a condensation reaction?

A

bonds are broken and new bonds reformed in different places producing new molecules. water is formed.

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16
Q

what are pentose monosaccharides?

A

pentose monosaccharides are sugars that contain 5 carbon atoms. examples are ribose and deoxyribose.

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17
Q

what is starch made of?

A

many alpha glucose molecules joined by glycosidic bonds to form 2 slightly different polysaccharides known collectively as starch

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18
Q

what is amylose?

A

one of the polysaccharides in starch is called amylose. amylose is formed by alpha glucose molecules joined together only by 1-4 glycosidic bonds.

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19
Q

what is amylopectin?

A

the other starch polysaccharide is called amylopectin. amylopectin is made by 1-4 glycosidic bonds between alpha glucose molecules but also glycosidic bonds between carbon 1 and carbon 6 on 2 glucose molecules

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20
Q

what are the key properties of amylopectin and glycogen?

A

they are insoluble, branched and compact. these properties mean they are ideally suited to the storage roles that they carry out.

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21
Q

what are hydrolysis reactions?

A

to release glucose for respiration, starch or glycogen undergo hydrolysis reactions, requiring the addition of water molecules. the reactions are catalysed by enzymes.

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22
Q

how is cellulose formed??

A

The only way beta glucose molecules can join together and for a polymer is if alternate beta glucose molecules are turned upside down. when a polysaccharide is formed from glucose in this way it is unable to coil or form branches. a straight chain molecule is formed called cellulose.

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23
Q

what molecules are reducing sugars?

A

all monosaccharides and some disaccharides (for example maltose and lactose) are reducing sugars

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24
Q

what happens when reducing sugars are mixed with Benedicts reagent and warmed?

A

a brick red precipitate forms indicating a positive result

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25
Q

what happens in a Benedicts test for non-reducing sugars?

A

non reducing sugars do not react with Benedicts solution and the solution will remain blue after warming, indicating a negative result.

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26
Q

how can a non reducing sugar such as sucrose give a positive result?

A

if sucrose is first boiled with dilute hydrochloric acid it will give a positive result as the sucrose has been hydrolysed by the acid

27
Q

why are lipids not soluble in water?

A

lipids are not soluble in water as they are non-polar molecules. the even distribution of electrons in the outer shell mean that there are no positive or negative areas within the molecules and for this reason lipids are not soluble in water

28
Q

what type of complex molecules are lipids?

A

lipids are large complex molecules known as macromolecules, which are built from repeating units, or monomers, like polysaccharides.

29
Q

what is a triglyceride?

A

a triglyceride is made by combining one glycerol molecule with 3 fatty acids

30
Q

how are triglycerides formed?

A

the hydroxyl (OH) groups interact, leading to the formation of 3 water molecules and bonds between the fatty acids and the glycerol. these are called ester bonds and their reaction is called esterification

31
Q

what needs to happen when triglycerides are broken down

A

when triglycerides are broken down, 3 water molecules need to be supplied to reverse the reaction. this an example of a hydrolysis reaction

32
Q

why are some fatty acids called ‘saturated’

A

fatty acids that have no double bonds present between the carbon atoms are called saturated, because all the carbon atoms form the maximum number of bonds with hydrogen bonds

33
Q

why are some fatty acids called ‘unsaturated’

A

a fatty acid with double bonds between some of the carbon atoms is called unsaturated

34
Q

what are phospholipids?

A

phospholipids are modified triglycerides and contain the element phosphorus

35
Q

properties of phospholipid tail

A

the non-polar tails are repelled by water. they are hydrophobic.

36
Q

properties of phospholipid head

A

the charged heads will interact with, and are attracted to, water. they are hydrophilic

37
Q

role of cholesterol

A

it is positioned between the phospholipids with the hydroxyl group at the periphery of the membrane. this adds stability to cell membranes and regulates their fluidity by keeping membranes fluid at low temperatures and stopping them becoming too fluid at high temperatures

38
Q

roles of lipids

A
  • membrane formation and the creation of hydrophobic barriers
  • hormone production
  • electrical insulation necessary for impulse transmission
  • waterproofing, for example in bird’s feathers on plant leaves
  • thermal insulation to reduce heat loss for example, in penguins
  • cushioning to protect vital organs such as the heart and kidneys
  • buoyancy for aquatic animals like whales
39
Q

what test is used to identify lipids?

A

emulsion test

40
Q

what are peptides?

A

peptides are short chains of amino acid molecules bonded by peptide bonds

41
Q

synthesis of dipeptides

A
  • the hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid
  • a peptide bond is formed between the amino acids and water is produces (this is an example of a condensation reaction)
  • the resulting compound is a dipeptide
42
Q

structure of amino acids

A

all amino have the same basic structure. Different R-groups result in different amino acids

43
Q

how is a polypeptide formed?

A

when many amino acids are joined together by peptide bonds a polypeptide is formed

44
Q

levels of protein structure

A

see goodnotes

45
Q

how are peptides broken down?

A

proteases are enzymes that catalyse the reverse reaction - turning peptides back into their constituent amino acids. a water molecule is used to break the peptide bond in a hydrolysis reaction, reforming the amine and carboxylic acid groups

46
Q

types of proteins

A

see goodnotes

47
Q

what are the 2 types of nucleic acid?

A

DNA and RNA

48
Q

how are nucleotides linked?

A

nucleotides are linked together by condensation reactions to form a polymer called a polynucleotide

49
Q

what is a nucleotide made up of?

A
  • a pentose monosaccharide containing 5 carbon atoms
  • a phosphate
  • a nitrogenous base
50
Q

what are nucleic acids?

A

they are large polymers formed from many nucleotides

51
Q

how are phosphodiester bonds formed?

A

the phosphate group at the fifth carbon of the pentose sugar (5’) of one nucleotide forms a covalent bond with the hydroxyl (OH) group at the third carbon (3’) of the pentose sugar of an adjacent nucleotide. these bonds are called phosphodiester bonds.

52
Q

what do these phosphodiester bonds form?

A

they form a long, strong sugar phosphate ‘backbone’ with a base attached to each sugar

53
Q

how are phoshodiester bonds broken

A

the phosphodiester bonds are broken by hydrolyse, releasing the individual nucleotides

54
Q

what is the sugar in deoxyribonucleic acid (DNA)

A

deoxyribose - a sugar with one fewer oxygen atoms than ribose

55
Q

structure of DNA

A

it is made up of 2 strands of polynucleotides coiled into a helix, known as the DNA double helix

56
Q

structure of strands

A
  • held together by hydrogen bonds between the bases
  • each strand has a phosphate group (5’) at one end and a hydroxyl group (3’) at the other end
  • the strands are antiparallel
57
Q

base pairing rules

A

-A + T form 2 hydrogen bonds
-G + C form 3 hydrogen bonds
this is known as complementary base pairing

58
Q

what is RNA?

A

Ribonucleic acid (RNA) plays an essential role in the transfer of genetic information from DNA to the proteins

59
Q

how are RNA nucleotides different to DNA nucleotides?

A
  • the pentose sugar is ribose rather than deoxyribose
  • T is replaced with U
  • U forms 2 hydrogen bonds with A
60
Q

how do RNA nucleotides form polymers?

A

formation of phosphodiester bonds in condensation reactions

61
Q

what happens to RNA molecules after protein synthesis?

A

the phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused

62
Q

DNA replication

A

see goodnotes

63
Q

protein synthesis

A

see goodnotes

A level Biology (3 decks)

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