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alevel bio > Chap 2:Biological Molecules (proteins+lipids+nucelic acids) > Flashcards

Chap 2:Biological Molecules (proteins+lipids+nucelic acids) Flashcards

1
Q

What are the monomers of proteins and how many different types are there

A

Amino acids,
20 different types
(So trillions of combinations of polypeptides)

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2
Q

Describe the structure of an amino acid

A

Has on carboxylic group, one amine group, one hydrogen atom and one R group

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3
Q

What is meant by amino acids being amphoteric

A

They contain both acidic (amine) and basic(carboxyl) groups

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4
Q

What is an R group and how can they differ

A

A variable chain in an amino acid which is how each amino acid differs,
The can vary in size and polarity

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5
Q

How is a polypeptide chain formed

A

2 amino acids react together in condensation reaction to form a dipeptide and releasing water. The dipeptide is held together by a peptide bond.
This occurs when ther hydroxyl from the carboxyl group reacts with a H from the amine group of another amino acid.

Polypeptides only form however when multiple amino acids are bonded together by peptide bonds

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6
Q

Explain how to test for the presence of a protein

A

1)add 5% sodium hydroxide to the food solution to make it alkaline
2)add a few drops of copper (ii) sulfate
And now biuret reagent is formed
-3)add biuret reagent to the sample
-colour change of blue to lilac/purple shows that a protein is present

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7
Q

Why may a biuret test still be negative even if amino acids are present in the solution

A

-because atleast 2 dipeptides are needed to be present (so a polypeptide chain)
-so amino acids and a dipeptide alone will not work

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8
Q

What occurs in a hydrolysis reaction with a polypeptide chain

A

Water is added and so the peptide bond is broken , and amino acids are formed as products

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9
Q

What is the primary structure of a protein

A

The specific sequence of amino acids, bonded by covalent peptide bonds

-the primary structure is what determines the shape and function of the protein and is specific for each protein

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10
Q

What is the secondary structure of a protein

A

The folding of the polypeptide chain by hydrogen bonds to form either an alpha helix or a beta pleated sheet

This occurs when weak negatively charged oxygen atoms interact with weak positively charged hydrogen atoms to form hydrogen bonds.

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11
Q

Describe how an alpha helix forms

A

The Oxygen on the carbonyl of one amino acid forms a hydrogen bond with the hydrogen on the amino acid that is 4 down to chain (so on amino acid 5)

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12
Q

Describe the structure of an alpha helix

A

-has a helical structure
-each turn has 3.6amino acids
-each amino acid is hydrogen bonded to an amino acid 4 down the chain
-r groups stick outwards

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13
Q

Describe the structure of a beta pleated sheet

A

-pleated sheet
-hydrogen bonds form between parralel amino acids on the backbone
-r groups extend upwards and outwards

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14
Q

Explain how a beta pleated sheet forms

A

A single polypeptide chain folds so that 2 or more segments of the polypeptide chain are parrale to ecah other,
where hydrogen bonds will now form between amino acids that are parrallel to each other. Between oxygen on carbonyl of one amino acid and hydrogen on amine group in another amino acid

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15
Q

Describe properties of the hydrogen bonding in the secondary structure of a protein

A

Hydrogen bonding keeps it stable and in shape
howver high temperatures and ph changes can damage the shape

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16
Q

Describe the tertiary structure of a protein

A

The overall 3D structure of a single polypeptide chain (which bends and fold extensively into a compact structure), and is determined by the interactions between r groups and the properties of r groups

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17
Q

State the different types of bonding that can occur in the tertiary structure of a protein in order from strongest to weakest and then give a description of each

A

-disulfide bridges, between sulfur atoms in r group ( but can only occur between cysteine amino acids)
-ionic bonds, between oppositely charged r groups
-weak hydrophobic interactions, between non polar r groups
-hydrogen bonds, between polar r groups

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18
Q

In terms of the different types of bonds that can be present in the tertiary structure, explain how ph changes and temperature can affect each

A

-for disulfide bridges, they have increased stability to temperature and ph change
-ionic bonds can be broken by changes in ph
-hydrogen bonds can be broken by both temperature changes and ph changes

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19
Q

Explain what is meant by the quaternary structure of a protein

A

The specific 3D shape of a protein, determined by the multiple polypeptide chains and or the prosthetic groups bonded together

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20
Q

Give an example of two protiens which have a quaternary structure in them

A

Haemoglobin and collagen

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21
Q

Describe the structure of haemoglobin

A

-Made up of 4 polypeptide chains in total, so 2 a globins and 2 beta globins
-it has 4 prosthetic groups, called haem which has Fe2+ in it
-hydrophobic r groups face inwards and hydrophilic r groups faces outwards which is why it is soluble
-it is held together by disulfide bonds

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22
Q

Describe the primary structure of collagen

A

-it has a repetitive structure, where every 3rd amino acid is glyceine(which is the smallest amino acid as its r group is a h atom which allows the polypeptide chains to wrap tightly around each other)
-it also has proline and hydroxyproline amino acids present

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23
Q

Describe the secondary and tertiary structure of collagen

A

-a helix shape (secondary structure)
-but does not have a tertiary structure

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24
Q

Describe the quaternary structure of collagen

A

-three polypeptide chains of collagen are held tightly together by hydrogen bonds to form a collagen molecule
-the ends of each molecule is staggered so that weak spot do not occur between them
-covalent bonds also form between r groups on amino acids on interacting triple helices
-these covalent bonds can therfore form cross linkages
-cross linkages can hold them together into r fibrils
Fibrils can form strong fibres

25
Q

Give an example of a globular protein and then give the general properties of globular proteins

A

-haemoglobin

compact and roughly spherical
-irregular and wide range of r groups
-hydrophobic r groups inwards and hydrophilic r groups outwards so soluble
-so plays a physiological role , eg involved in metabolic reactions

26
Q

Give an example of a fibrous protein and then give the properties of them

A

Collagen

-long strands, with cross linkages due to hydrogen bonds
-repetitive pattern of r groups with a limited range of
-many hydrophobic groups so generally not soluble in water
-plays a structural role, because repetive sequence makes them strong and organized

27
Q

Give and describe 4 functions of collagen

A

-structurally flexible so can from connective tissue (eg in tendons and ligaments)
-high tensile strength so can withstand large pulling forces without breaking due to hydrogen bonds present
-stable due to large number of hydroxyproline and proline groups which repel each other
-insoluble due to long length, bc takes a while to dissolve

28
Q

What is a lipid

A

A macromolecules which contains carbon hydrogen and oxygen,(but has a lower proption of oxygen than carbs)
-they are non polar and hydrophobic

29
Q

Give 2 reasons why lipids are usueful as a storage molecule

A

-non polar and hydrophobic so are insoluble in water, therfore do not effect the osmotic effect of cells
-upon oxidation they release more energy per gram than carbohydrates because the many C-H bonds release large mount of energy when broken down

30
Q

What is a triglyceride made up of and explain how they are formed

A

One glycerol monomer, bonded to three fatty acid chains
-occurs through esterfication reactions which is where the H from the hydroxyl of the glycerol molecule bonds to the OH of the carboxyl of the fatty acid, forming an ester bond
-one ester bond releases one water molecule
-therefore to form one triglyceride, 3 water molecules are released

31
Q

Name two groups present in a fatty acid

A

Carboxyl group
Methyl group

32
Q

Explain the three ways in which fatty acids can vary

A

-by the length of the hydrocarbon chain
—can be saturated so have no double bond present between carbon atoms
-can be unsaturated, so has 1 or more double bonds present between carbon atoms

33
Q

Explain the types of unsaturated fatty acids, and the differences between them

A

-can be a cis fatty acid,
so has hydrogen atoms on the same side of the double bond,
-this causes it to be bent. ( so it has a kink, which makes it difficult to pack and therfore is a liquid at room temperature)
-these are metabolized by enzymes

-can be a trans fatty acid
So has hydrogen atoms on both sides of the double bond
-these are not metabolized by enzymes as it is difficult to form enzyme substrate complexes

34
Q

Explain the differences between saturated and unsaturated fatty acids

A

-saturated, have no double bonds between carbon atoms
-so they are straight, and this causes them to pack tightly together
-which results in solids at room temperature
-they therfore have higher melting point than unsaturated fatty acids

-unsaturated have d1 or more double bonds between carbon atoms,
-so unstayrtd cis fatty acids, which have h atoms on one side of the double bond, are bent and so form kinks
-this makes it difficult for them to pack tightly with ecah other
-so they form liquids at room temperature
-they have lower melting points than saturated fatty acids

35
Q

Explain the four functions of triglycerides

A

-good energy stores
Because they store more energy per gram than carbohydrates due to the presence of many C-H bonds, so upon oxidation, these bonds release large Amun ts of energy used to make atp

-used for insulation
Triglycerides form part of the myelin sheath that surrounds nerve impulses which therfore increases the transmission of nerve impulses
-they also form part of the adipose layer below the skin in mammals

-buoyancy
-triglycerides have low density which increases the ability for mammals to float on water

Protection
-forms part of the adipose tissue in mammals under the skin which protects organs from damage

36
Q

State how triglycerides are stored in plants and then how they are stored in mammals

A

-stored as oils in seeds and fruits in plants, bc of the kink in the cis unstarted fatty acid, which makes it difficult to pack together

-stored as adipose tissue under the skin in mammals

37
Q

Explain how phospholipids are formed

A

The hydroxyl group of one glycerol molecule binds to a hydrogen on a phosphate group
during a condensation reaction, to produce a phosphate hed,
which releases one water molecule
The phosphate group and glycerol are bonded together through phosphodiester bonds

-the OH group of tw fatty acids bond to the H on a glycerol molecule
thro a condensation reaction
therfore two molecules of water are released
And so the fatty acid and glycerol are bonded together though ester bonds

38
Q

Explain the composition of a phospholipid

A

-polar, hydrophilic, phosphate head(consisting of one glcvyerol bonded to one phosphate group through phosphodiester bonds)

-bonded to two fatty acids which are
Non polar and hydrophobic

(Where the glycerol form the phosphate group is bond to the two fatty acids through 2 ester bonds)

39
Q

Why can a phospholipid be described as ampiphatic

A

Because it contains both hydrophobic and hydrophilic parts

40
Q

If a phospholipid is placed in a Drop of water, what does it form and what dos this mean

A

Forms a micelle
So has hydrophilic heads on the outside and hydrophobic heads on the inside

41
Q

Explain how phopsholipds control membrane orientation

A

-because they control membrane orientation, because the weak hydrophobic interactions between the fatty acid tails and the membrane proteins holds the proteins together but also allows movement between the layer

42
Q

Explain how phospholipid contribute to the fluidity of the membrane

A

-saturated fatty acid tails are straight and so can easily pack together
So they make the membrane less fluid

-unstaturated fatty acids can have kinks so makes it difficult to pack together
So they make the membrane more fluid

43
Q

Describe how to conduct the lipid emulsion test

A

-solid food sample should be ground up using s pestle and mortar
-add ethanol and food sample to a test tube and mix together
-add this ethanol and food sample to cold distilled water
-if a lipid is present then a milky emulsion will form, but if no lipid is present then the solution remains clear

-

44
Q

Explain why during the lipid emulsion test, the food sample must first be added to ethanol

A

-It cant be added to water because lipids are non polar so will not dissolve in the water
-however lipids can dissolve in organic solvent such as ethanol

45
Q

Explain fully what a nucleic acid is

A

Macromolecules that are polymers

-they are macromolecules because they are large molecules with a large molecular mass
-they are polymers because they are made up of many monomer (nucleotides) in a long chain

46
Q

What components are nucleic acids made up of

A

-carbon, hydrogen and oxygen
-nitrogen and phosphorus

47
Q

Explain how a polynucleotide is formed

A

In the 5’ to 3’ direction, the hydroxyl on carbon three of the pentose sugar of one nulceotde, forms a phosphodiester bond with the phosphate group on the next nucleotide,
This occurs through a condensation reaction because a water molecule is released whilst doing so

In the 3’ to 5’ direction, the hydroxyl on carbon 5 of the pentose sugar of one nucleotide, forms a phosphodiester bond with the phohate group on the next nucleotide,
Through a condensation reaction because a water meoclue is released whilst doing so

48
Q

Give 6 differences between dna and rna

A

-dna has two strands
-rna has one strand

-dna has a deoxyribose sugar
-rna only has a ribose sugar

-dna contains, adenine, thymine, cytosine and guanine
RNA contains adenine, uracilm cytosine and guanine

-dna is a longer molecule than rna
-rna is a shorter molecule than rna

-dna forms a double helix
-rna forms a straight chain

-ratio of purines to pyramides in dna is 1;1. Because of the double stranded structure and because a purine always bins ot a pyramide
-but ratio of purines tp pyramides in rna varies

49
Q

Gicle the differences between a purine and a pyramide and give examples of each

A

Purines have a double ring structure
Pyramides have a single ring structure

Purines are adenine and guanine
Pyramidunes are thymine, cytosine and uracil

50
Q

Explain what atp is

A

Adenosine triphosphate is an energy carrying molecule which is a type of nucleotide,
And contains three phosphate groups

51
Q

Explain how ther number of phosphate groups on a nucleotide can vary

A

Before a nucleotide has been added to a nucleotide chain it exists with three phosphate groups

But once it is added ti the polynucltide chain, it loses two of these phohate groups (which eg is why in a chain of dna or rna, each nucleotide only has one phosphate group)

52
Q

What is adenosine

A

The sugar base formed When the pentose sugar ribose is attached to the nitgrenous base adenine

53
Q

What are the three components if a nucleotide

A

Pentose sugar, ntorgienous base and phosphate groups

54
Q

State the names of three types of nucleotides (which have the sugar base adenosine in them) and give the corresponding number of phosphate groups

A

AMP, one phohate group
ADP, two phosphate groups
ATP, three phosphate groups

55
Q

Why is atp described as phosphorylated

A

Due to the presence of 3 phosphate groups added to the ribose sugar

56
Q

How are complimentary bases held together

A

Joint together by hydrogen bonds

57
Q

How many base pairs are there in one turn of a double helix

A

10 base pairs

58
Q

State where nucleic acids are found in for eukaryotes and for prokaryotes

A

Eukaryotes- inside the nucleus
Prokatote- fudn in plasmids(rings of dna)

alevel bio (11 decks)

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