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Biology AS level Paper 1 > Chapter 1 Biological molecules > Flashcards

Chapter 1 Biological molecules Flashcards

1
Q

1.1 What are the features of Carbon?

A
  • Each C atom make 4 bonds
  • They form a tetrahedral shape
  • Very readily form bonds with other C atoms
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2
Q

1.1 How are molecules based on carbon constructed/formed?

A

Carbon atoms very readily form bonds with other carbon atoms= allows sequence of carbon atoms (of various lengths) to be built up= which form a backbone by which other atoms can be attached to (in living organisms only a few other atoms can be attached to carbon) = permitting an immense no. of diff. types and sizes of molecules to be constructed all based on carbon

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3
Q

1.1 What are carbon-containing molecules known as? And what elements do most of them contain?

A

They are known as organic- molecules/compounds. All of them contain the elements carbon, hydrogen and oxygen (Less frequently they contain nitrogen, sulphur and phosphorus).

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4
Q

1.1 What is a monomer? And give an example.

A

A monomer refers to smaller units which may be joined to form polymers. E.g. Amino acids and simple sugars

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5
Q

1.1 What is a polymer? And give an example.

A

A polymer refers to a long-chain molecule made up of several monomers linked toegther by chemical bonds. E.g. proteins and carbohydrates

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6
Q

1.1 What is the basic monomer unit in carbohydrates? And what is a single monomer in carbohydrates called?

A

A sugar, otherwise known as a saccharide. A single monomer is therefore called monosaccharide.

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7
Q

1.1 What is pair of these monomers in carbohydrates called?

A

Disaccharide.

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8
Q

1.1 What are many of these monomers in carbohydrates called?

A

Polysaccharide.

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9
Q

1.1What are the characteristics of monosaccharides

A

-Sweet tasting
-Soluble
- Have a general formula (CH2O)n’ (n can be any no. from 3-7)
-All sugars end with -ose

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10
Q

1.1 What are the Greek terms used when referring to chemicals?

A

mono-one
di-two
tri-three
tetra-four
penta-five
hexa-six
poly-many

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11
Q

1.1 What are the characteristics of glucose?

A
  • Glucose is perhaps the best-known monosaccharide
  • It is a hexose (6-carbon) sugar
  • Has formula C6H12O6
  • It has two isomers; (alpha) α-glucose and (beta) β-glucose
  • Chain of C atoms long enough to close up on itself and form a ring
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12
Q

1.1 What are isomers?

A

Isomers refer to organic molecules /compounds that have the same chemical formula but diff. structural/molecular formula

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13
Q

1.1 What is the difference between (alpha) α-glucose and (beta) β-glucose

A

Alpha glucose= OH group falls below carbon 1
Beta glucose= OH group falls above carbon 1
(Each line represents a covalent bond)

https://byjus.com/question-answer/the-difference-between-alpha-and-beta-glucose/

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14
Q

1.1 What is reduction? And what are reducing sugars? (include which carbohydrates are reducing sugars)

A

Reduction refers to a chemical reaction involving the gain of electrons. Reducing sugars are sugars which donate electrons to / reduce another chemical (in this case Benedict’s reagent). All monosaccharides and some disaccharides (e.g. maltose) are reducing sugars.

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15
Q

1.1 What happens when a reducing sugar is heated with Benedict’s reagent?

A

Benedict’s reagent (alkaline solution of copper (ll) sulfate ) is heated with a reducing sugar to form copper (l) oxide (orange-brown precipitate)

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16
Q

1.1 What is the Benedict’s test? (include a positive result)

A
  1. Add 2cm^3 of the food sample to the test tube (if not in liquid state already, grind it in water first)
  2. Add an equal volume of Benedict’s reagent
  3. Heat the mixture in a gently boiling water bath for 5 minutes

The presence of a reducing sugar is indicated by the change of Benedict’s reagent colour from a blue to an orange-brown colour

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17
Q

1.1 What are the results of the benedict’s test according to the concentration of the reducing sugars

A

None - Blue
Very low- Green
Low- Yellow
Medium- Brown
High- Red

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18
Q

1.2 What are some examples of monosaccharides?

A

Glucose, fructose and galactose

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19
Q

1.2 What are some examples of disaccharides?

A

Maltose= Alpha glucose +Alpha glucose
Sucrose= Alpha glucose +fructose
Lactose= Alpha glucose+ galactose

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20
Q

1.2 What are some examples of polysaccharides?

A

Cellulose = provides structural support in plants (made from β-glucose molecules)
Starch = storage molecule in plants (made from α-glucose)
Glycogen - storage molecule in animals (made from α-glucose)

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21
Q

1.2 Explain and identify the process which leads to the joining of monosaccharides?
(include the bond formed)

A

Monosaccharides can be joined together to form disaccharides and polysaccharides through a condensation reaction (the reaction in which a water molecule is removed between the reacting molecules and a bond is formed).
-An oxygen bridge, called a glycosidic bond, is formed between the two monosaccharides = Water is released as a product.
-Reaction is controlled by enzymes.

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.khanacademy.org%2Fscience%2Fap-biology%2Fchemistry-of-life%2Fintroduction-to-biological-macromolecules%2Fa%2Fintroduction-to-macromolecules&psig=AOvVaw1cEAGGxM8a5mMacq_PCYeY&ust=1672156495663000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCJizv8HSl_wCFQAAAAAdAAAAABAE

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22
Q

1.2What is a glycosidic bond?

A

A covalent bond formed between two monosaccharides in a condensation reaction, which can be broken by a hydrolysis reaction, to release the monosaccharide units.

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23
Q

1.2 Explain and identify the process which leads to the breakdown of these joined monosaccharides?

A

Polysaccharides and disaccharides can be broken down to form monosaccharides through hydrolysis
-Under suitable conditions, when a water molecule is added, the glycosidic bond joining the monosaccharides break= releasing the constituent monosaccharides

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.khanacademy.org%2Fscience%2Fap-biology%2Fchemistry-of-life%2Fintroduction-to-biological-macromolecules%2Fa%2Fintroduction-to-macromolecules&psig=AOvVaw0rJYvOMRZNLW54FZYJkkY8&ust=1672156425437000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCJio_5_Sl_wCFQAAAAAdAAAAABAE

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24
Q

1.2 What are non-reducing sugars?

A

Non-reducing sugars are sugars that don’t react with Benedict’s reagent. And need to be broken down into its monosaccharide constituents by hydrolysis in order to be identified

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25
Q

1.2What is the test of non-reducing sugars

A
  1. Add 2cm^3 of the food sample to the test tube (if not in liquid state already, grind it in water first)
  2. Add an equal volume of Benedict’s reagent
  3. Heat the mixture in a gently boiling water bath for 5 minutes (If the Benedict’s reagent remains blue then a reducing sugar isn’t present)
  4. Add another 2cm^3 of the food sample to 2cm^3 of dilute hydrochloric acid in a test tube and place the test tube in gently boiling water for 5 minutes (the dilute HCL will hydrolyse any disaccharide present into its constituent monosaccharides)
  5. Slowly add some sodium hydrogencarbonate solution to the test tube (in order to neutralise the HCL (Benedict’s reagent won’t work in acidic conditions) Then test with pH paper to make sure the solution is alkaline
  6. Retest the resulting soltion by heating it with 2cm^3 of Benedict’s reagent in a gently boiling water bath for 5 minutes
  7. If non-reducing sugar is present in og. sample, the Benedict’s reagent would now trun orange-brown (due to the reducing sugars produced from the hydrolysis of the non-reducing sugar)
26
Q

1.2What is the test for starch? (include the positive result)

A
  1. Place 2cm^3 of the sample being tested into a test tube/ add two drops of the sample into a depression on a spotting tile
  2. Add 2 drops of iodine solution and shake/stir
    - The presence of starch is indicated by its ability to change the colour of iodine in iodine solution from yellow to a blue black colour
27
Q

1.3 What is starch? And what is it made up of?

A

Starch is a ploysaccharide found in several parts of a plant in the form of small grains such as, potato tubers.
It is made up of two polysaccharides; amylose and amylopectin (both made up of chains of alpha-gluocse monosaccharides)

https://www.google.com/url?sa=i&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTuber&psig=AOvVaw26-mOsLhwXyO6xfCiEC3PE&ust=1672162814457000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCICH04bql_wCFQAAAAAdAAAAABAE

28
Q

1.3 What is amylose? (include its structure)

A

Amylose is a polysaccharide made up of unbranched chains of alpha glucose monosaccharides bonded together by glycosidic bonds through several condensation reactions and is one of the two components of starch.
- Alpha glucose molecules are unbranched and is wound into a tight coil= making it compact= so it is an ideal storage molecule
- The alpha glucose is arranged in helix
- There are only 1-4 glycosidic bonds present

https://futurefoodchemist.weebly.com/amylose-or-amylopectin.html

29
Q

1.3 What is amylopectin? (include its structure)

A

Amylopectin is a ploysaccharide made up of branched chains of alpha glucose monosaccharides bonded by glycosidic bonds through several condensation reactions and is one of the two components of starch.
- Alpha-glucose molecules are branched
- Contains both 1,4 and 1,6 glycosidic bonds
- It is more globular in shape

https://futurefoodchemist.weebly.com/amylose-or-amylopectin.html

30
Q

1.3 What is starch’s structure?

A

Starch is suited for its function (energy storage) because:
- It is a ploysaccharide= Large molecule= insoluble = doesn’t affect WP of cell + osmosis (doesn’t tend to draw in water by osmosis)
- Made up of amylose which has an unbranched structure, leading it to coil and form a helix= means that starch is compact= can fit a lot of glucose molecules in a small space
- Made up of amylopectin which has a branched structure= increases SA for rapid hydrolysis of starch back into glucose= can then be readily transported for respiration and photosynthesis

31
Q

1.3 What is glycogen? (include its structure)

A

Glycogen is a ploysaccharide made up of highly branched chains of alpha-glucose monosaccharides and is stored as small granules mainly in the liver and muscle cells.
It is suited for its functions (enegry storage) because:
- It is a polymer made from repeating alpha-glucose subunits/monosaccharides that branch
- There are also 1-4 and 1-6 glycosidic bonds
- It is a ploysaccharide= Large molecule= insoluble = doesn’t affect WP of cell + osmosis (doesn’t tend to draw in water by osmosis)
- 1-6 glycosidic bonds= Highly branched structure= increases SA for rapid hydrolysis of glycogen back to glucose= can be readily transported for respiration= therefore enable movement

32
Q

1.3 What is cellulose?
(include its structure)

A

Cellulose is a ploysaccharide made up of beta-glucose monosaccharides and is a major component of plant cell walls.
It is suited for its function (structure and strength) because:
- It is a polysaccharide made up of beta-glucose
- Has 1,4 glycosisdic bonds
- It is a ploysaccharide= Large molecule= insoluble = doesn’t affect WP of cell + osmosis (doesn’t tend to draw in water by osmosis)
- Cellulose has straight unbranched chains= allows the chains of beta-glucose to get close together= hydrogen bonds form cross-linkages with adjacent chains= the overall number of hydrogen bonds, contributes considerably to the strength of the cellulose molcule and thus the cellulose cell wall
- Cellulose molecules are grouped together to form microfibirls= microfibrils group together to form macrofibrils= macrofibrils group together to form fibrils = give a great amount of strength to the cellulose cell wall= prevents the plant cell from bursting as water enters by osomosis= does this by exterting an inwards pressure which stops any further influx of water

33
Q

1.4 What characteristics to lipids have?

A
  • Contain carbon, hydrogen and oxygen
  • The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
  • Insoluble in water
  • Soluble in organic solvents (e.g. alcohols, acetons)
34
Q

1.4 What are the three main types of lipids?

A
  • Triglycerides (fats and oils )
  • Phospholipids
  • Waxes
35
Q

1.4 What are the roles of lipids?

A

Phospholipids:
- Main role is a structural role (e.g. in building up cell membranes)
- They allow the membrane to be flexible
- They allow the transfer of lipid soluble molecules
Triglycerides:
– Good source of energy (when oxidised lipids provide more than twice the energy as carbohydrates)
Other roles are:
- Waterproofing (plants and insects have waxy cuticles that conserve water and mammals produce an oily secretion from sebaceous glands in skin)
- Insulation (fats are slow conductors of heat and when stored beneath the body surface, it helps to retain body heat)
- Protection (Fat often stored around delicate organs such as, kidneys)

36
Q

1.4 How do fats and oils vary in terms of their characteristics?

A

Fats:
- Solid at room temperature (10-20 celcius)
- Generally made of saturated fatty acids
Oils
- Liquid at room temperature (10-20 celcius)
- Made of unsaturated fatty acids

37
Q

1.4 How are triglycerides formed? (include bond formed, type of reaction and whether it can be reversed or not)

A

Each of the three fatty acids (can all be the same- simple triglyceride- or different - mixed triglyceride-) form a bond with each of glycerol’s three carbons in a codensation reaction which releases three molecules of water. The bond is known as an ester bond (type of covalent bond). This reaction can also be reversed through a hydrolysis reaction.

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.shutterstock.com%2Fsearch%2Ftriglycerides&psig=AOvVaw2YvLLOguaXXfb5cSSE4ZVa&ust=1672339430783000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCPjb4__7nPwCFQAAAAAdAAAAABAR

38
Q

1.4 What is the structure of a fatty acid? And how do fatty acids vary?

A

A fatty acid has a carboxyl group/ carboxylic acid (-COOH) with a hydrocarbon chain attached to it (represented by R). So fatty acids can be represented by the formula RCOOH.
All triglycerides have the same glycerol molecule but different fatty acids. The hydrocarbon chain attached to the carboxylic acid in a fatty acid may be saturated or unsaturated (this causes variations in fatty acids and therefore triglycerides)

39
Q

1.4 What is the difference between saturated and unsaturated fatty acids? And what are the types of unsaturated fatty acids? (include the impact of unsaturated fatty acids)

A

Saturated fatty acids have no carbon-carbon double bonds (meaning all their carbon atoms are bonded to the max. no of hydrogen atoms)
Unsaturated fatty acids do have carbon-carbon double bonds. Mono-unsturated fatty acids have one carbon-carbon double bonds whereas, polyunsaturated fatty acids have more than one carbon-carbon double bonds.
The carbon-carbon double bonds cause the molecule to have a bend/kink. Therefore, the fatty acid molecules can’t pack together so closely, making them liquid (oils) at room temp.

https://www.google.com/url?sa=i&url=https%3A%2F%2Fbyjus.com%2Fbiology%2Fdifference-between-saturated-and-unsaturated-fats%2F&psig=AOvVaw004Xn5d3hdLmO-Av6ZN5DX&ust=1672340431499000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCNicid3_nPwCFQAAAAAdAAAAABAE

40
Q

1.4 How do phospholipids form? (include bond formed and resulting structure)

A

Two fatty acids and a phosphate molecule each bond with each of glycerol’s three carbon atoms. The bond formed is an ester bond. This also results in hydrophobic/non-polar tails (fatty acids) and a hydrophillic/polar head (phosphate group)

https://www.google.com/url?sa=i&url=https%3A%2F%2Fstudymind.co.uk%2Fnotes%2Fphospholipids-introduction%2F&psig=AOvVaw3cfS5nEmTpoZpDqIqow9I_&ust=1672340951768000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCOjgvNWBnfwCFQAAAAAdAAAAABAE

41
Q

1.4 What is the difference betweem the hydrophobic/non-polar ‘tail’ and hydrophillic/polar’ head’?

A

The hydrophobic/non-polar ‘tail’ faces orients itself away from water but mixes readily with fat
The hydrophillic/polar ‘head’ attracts /interacts with water but not with fat.

42
Q

1.4 What are the two arrangements of phospholipids when in water?

A

A monolayer and a bilayered sheet

https://www.nature.com/scitable/topicpage/discovering-the-lipid-bilayer-14225438/

43
Q

1.4 What is the emergant property of phospholipids?

A

When phospholipid molecules are in water, the heads position themselves so they are as close to the water as possible and the tails position themselves so they are as far away from water as possible

44
Q

1.4 What is the test for lipids? (include positive result + control)

A

The test is known as the emulsion test and is carried out as follows;
1. Take a completely dry and grease-free test tube
2. To 2cm^3 of the sample being tested, add 5cm^3 of ethanol
3. Shake the tube thoroughly to dissolve any lipid in the sample
4. Add 5cm^3 of water and shake gently
A cloudly white emulsion indicates the presence of a lipid. And as a control, repeat the procedures using water instead of the sample; the result should be that the final solution remain clear.

45
Q

1.4 Why does the final solution turn cloudy?

A

The cloudiness is due to the lipid in the sample being disperesed in the water to form an emulsion.The light refracting from water to oil droplets, makes it appear cloudy.

46
Q

1.5 What are amino acids? And what are they made up?

A

Amino acids are the basic monomer units that combine to make a protien.
Amino acids are made up of the following:
- Amino/Amine group (-NH2)- a basic group
- Carboxyl group (-COOH)- an acidic group
- Hydrogen atom (-H)
- R group - a variety of different chemical groups (each amino acid has a diff. R group)

https://www.google.com/url?sa=i&url=https%3A%2F%2Falevelnotes.com%2Fnotes%2Fbiology%2Fbiological-molecules%2Fbiological-molecules%2Famino-acids&psig=AOvVaw2rRwRlfUycTAMiBv98UG5h&ust=1672342928368000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCMiG14OJnfwCFQAAAAAdAAAAABAE

47
Q

1.5 Why is the R group important?

A

The R group isn’t involved in the condensation reactions of amino acids but the structure of the R group dicatates the properties and nature of the amino acid

48
Q

1.5 What is a pair of amio acids called?

A

dipeptide

49
Q

1.5 What are more than two amino acid monomers called?

A

polypeptide

50
Q

1.5 How are polypeptides and dipeptides formed? (include the bond formed, the name of the reaction and if the reaction can be reversed)

A

A condensation reaction takes place. The removal of water is as a result of the -OH from the carboxyl group on one of the amino acids combining with an -H from the amine group of another amino acid. The carbon atom of the first amino acid and the nitrogen atom of the other amino acid are linked by a peptide bond resulting, in a dipeptide (further condensation reactions lead to the formation of polypeptides).This reaction can be reversed through a hydrolysis reaction; the addition of water breaks down the peptide bond giving its two constituent amino acids.

https://alevelnotes.com/notes/biology/biological-molecules/biological-molecules/amino-acids

51
Q

1.5 What is the primary structure of proteins? And how is it formed?

A

The primary structure of proteins refers to the sequence of amino acids in a polypeptide chain held together by peptide bonds.
This structure is formed as a result of a process known as polymerisation; the joining of monomers ,in this case amino acids, through a chemical reaction , in this case condensation reaction.

52
Q

1.5 Why is the primary structure important?

A

The primary structure of a protein determines the protein’s ultimate shape and function.

53
Q

1.5 How many polypeptide chains are proteins commonly made up of?

A

Some proteins are made up of just one polypetide chains. More commmonly however, a protein is made up of several polypeptide chains.

54
Q

1.5 What is the secondary structure of protein? And how is it formed? (include examples)

A

The secondary structure describes how the polypeptide chain can fold or curl into a regular, repeating 3D structure due to hydrogen bonding.
The hydrogen of the -NH group has an overall positive charge while the O of the C=O group has an overall negative charge. These two groups therfore, form weak hydrogen bonds, causing the shape to bend (Although hydrogen bonds are weak, hundreds of them keep the secondary structure stable).
The two main examples are:
α-helix - A spiral coil, held toegther by hydrogen bonds
ß-pleated – a sheet where the polypeptide chain folds into regular pleats held together by hydrogen bonds

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.shutterstock.com%2Fsearch%2Falpha-helix-protein&psig=AOvVaw34pkcmz8s2MwwMBgpEedk7&ust=1672395006229000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCLjUpITLnvwCFQAAAAAdAAAAABAE

55
Q

1.5Why is the 3-D shape of a protein important?

A

The 3-D shape of a protein is important when it comes to how it functions however it is the primary structure that determines the 3-D shape in the first place

56
Q

1.5 What is the teritiary structure? And how is it formed? (include how this structure is maintained)

A

A teritiary structure refers to the amino acid chain being twisted and folded further to give the polypeptide chain a unique 3D structure
It is maintained by a no. of different bonds:
- Disulfide bonds- Not common, fairly strong covalent bonds that are therefore not easily broken. It occurs between the two sulfur-containing R groups.
- Ionic bonds- Not common,strong bonds (weaker than disulfide bonds), which are formed between any carboxyl and amine group that aren’t involved in the formation of peptide bonds. They are easily broken by changes in pH.
- Hydrogen bonds- numerous but are easily broken by changes in pH and temperature

57
Q

1.5 What is the quaternary structure of proteins? And how is it formed? (include the definition of conjugated proteins and examples)

A

The quarternary structure of proteins describes to the combinatio of a no. of different polypeptide chains linked in various ways and associtaed non-protein (prosthetic) groups into a large, complex protein molecule.
Conjugated proteins refer to protein molecules that are joined with a prosthetic group. This structural feature affects the performance and functions of the molecules
An example of a quarternary structure is Heamglobin (contains iron)

58
Q

1.5 What is the test for protiens? (include positive result)

A

The biuret test is the test for proteins and is carried out as follows:
1. Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydrooxide soltion at room temperature
2. Add a few drops of dilute (0.05%) copper(II) sulfate soltion and mix gently
A positive result is the change in colour from blue to purple (indicating a protein is present)
OR
Simply refer to adding biuret reagent to test for a protein and if there is a purple colouration a protein is present, if not the solution should remain blue

59
Q

1.5 What are the two types of molecular shapes for proteins? (include examples and functions of each)

A
  • Fibrous proteins (e.g. collagen) have structural functions
  • Globular proetins (e.g. enzymes and heamoglobin) carry out metabollic functions
60
Q

1.5 What are fibrous proteins?

A

Fibrous proteins form long chains that run parallel to one another and are linked by cross-bridges, making them very stable molecules.

Biology AS level Paper 1 (3 decks)

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