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AS Biology > Chapter 3 - Biological Molecules > Flashcards

Chapter 3 - Biological Molecules Flashcards

Water, Carbohydrates, Lipids, Proteins, Nucleic Acids

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1
Q

What is a molecule?

A

The complex formed when two or more atoms bond together

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2
Q

What are covalent bonds?

A

Bond that occur when two atoms share a pair of electrons. The electrons used to form bonds are unpaired and present in the outer orbitals of the atoms.

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3
Q

What are the bonding rules for carbon, nitrogen, oxygen and hydrogen atoms?

A
  • Carbon atoms form 4 bonds
  • Nitrogen atoms form 3 bonds
  • Oxygen atoms form 2 bonds
  • Hydrogen atoms form 1 bonds
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4
Q

What is an ion?

A

An atom or molecule with an overall electric charge because the total number of electrons is not equal to the total number of protons

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5
Q

What is an ionic bond?

A

A chemical bond that involves the donating of an electron from one atom to another, forming positive and negative ions held together by the attraction of the opposite charges

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6
Q

What is a cation?

A

An atom or molecule that loses one or more electrons giving it a net positive charge.

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7
Q

What is an anion?

A

An atom or molecule that gains one or more electrons giving it a net negative charge.

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8
Q

What are ions in solution called?

A

Electrolytes

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9
Q

List all of the important cations in living organisms

A
  • Calcium ions (Ca2+)
  • Sodium ions (Na+)
  • Potassium ions (K+)
  • Hydrogen ions (H+)
  • Ammonium ions (NH4+)
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10
Q

What are calcium ions necessary for?

A

Nerve impulse transmission and muscle contractions

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11
Q

What are sodium ions necessary for?

A

Nerve impulse transmission and kidney function

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12
Q

What are potassium ions necessary for?

A

Nerve impulse transmission and stomata opening

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13
Q

What are hydrogen ions necessary for?

A

Catalysis of reactions of pH

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14
Q

What are ammonium ions necessary for?

A

Production of nitrate ions by bacteria

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15
Q

What are nitrate ions necessary for?

A

Nitrogen supply to plants for amino acid and protein formation

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16
Q

What are hydrogen carbonate ions?

A

Maintenance of blood pH

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17
Q

What are chloride ions necessary for?

A

Balance positive charge of sodium and potassium ions in cellsW

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18
Q

What are phosphate ions necessary for?

A
  • Cell membrane formation
  • Nucleic acid and ATP formation
  • Bone formation
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19
Q

What are hydroxide ions necessary for?

A

Catalysis of reactions and pH

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20
Q

List the 4 biological molecules and the element present in each of them

A
  • Carbohydrates - carbon, hydrogen, and oxygen usually in the ration Cx(H2O)x
  • Lipids - carbon, hydrogen, and oxygen
  • Proteins - carbon, hydrogen, oxygen, nitrogen, and sulphur
  • Nucleic acids - carbon, hydrogen, oxygen, nitrogen, and phosphorus
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21
Q

What are the monomers in carbohydrates called?

A

Saccharides (sugars)

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22
Q

What are the monomers in proteins called?

A

Amino acids

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23
Q

Why are some molecules polar?

A
  • In covalent bonds the atoms are not always shared equally by the atoms of different elements
  • The atoms with the greater share of negative electrons will be slightly negative compared with the other atom in the bond, which will be slightly positive
  • Polar molecules have regions of negativity and regions of positivity
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24
Q

Why is water is polar molecule?

A
  • Oxygen always has a much greater share of electrons in an O-H bond
  • Many organic molecules contain hydroxyl (OH) groups, and so are slightly polar; water is an example
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25
Q

What are hydrogen bonds, and what causes them?

A
  • Hydrogen bonds are relatively weak interactions
  • They are caused by polar molecules interacting with each other and forming bonds - hydrogen bonds
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26
Q

List the properties of water (6)

A
  • Liquid
  • Density
  • Solvent
  • Cohesion and surface tension
  • High specific heat capacity
  • High latent heat of vaporization
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27
Q

Why is water a liquid at room temperature?

A

The hydrogen bonds between water molecules make it more difficult for them to escape to become a gas

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28
Q

What is the importance of water being a liquid at room temperature, to living organisms? (4)

A
  • Provides habitats for living things in rivers, lakes and seas
  • Forms a major component of the tissues in living organisms
  • Provides a reaction medium for chemical reactions
  • Provides an effective transport medium e.g. in blood and vascular tissue
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29
Q

Describe how the density of water changes, as H2O changes state

A

Usually the solid is more dense than the liquid form of a substance.

However ice is less dense than water because as water goes from 4C to freezing point, the water molecules form a structure that is less dense than liquid water

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30
Q

What is the importance of water’s density to living organisms? (2)

A
  • If water was less dense, aquatic organisms would find it very difficult to float

Ice floats on water so:
* Aquatic organisms have a stable environment to live through in winter
* Ponds are insulated against extreme cold because the ice layer reduces heat loss from the pond

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31
Q

Why is water a good solvent? (2)

A
  • As it is polar, the positive and negative parts of the water molecules are attracted to the oppositely charged parts of the solute
  • Water molecules cluster around the charged parts of the solute molecules or ions, which helps to separate them and keep them apart
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32
Q

What is the importance of water being a good solvent to living organisms?

A
  • Molecules andirons can move around and react together in water e.g. as in the cytoplasm of cells, which is >70% water
  • Molecules and ions can be transported around living things whilst dissolved in water
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33
Q

Describe cohesion and surface tension of water

A
  • Water molecules demonstrate cohesion because hydrogen bonding between the molecules pulls them together
  • Water molecules demonstrate surface tension because they are more attracted to the water molecules beneath them than air molecules above, so the water contacts, giving the surface of the water the ability to resist a force applied to it
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34
Q

What is the importance of cohesion and surface tension of water to living organisms? (2)

A
  • Columns of water in plant vascular tissue are pulled up the xylem tissue together from the roots due to cohesion
  • Insects like pond-skaters can walk on water due to surface tension
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35
Q

Why does water have a high specific heat capacity?

A
  • Water molecules are held together quite tightly by hydrogen bonds
  • Therefore you need to put in a lot of heat energy to increase their kinetic energy and temperature
  • This means that water doesn’t heat up or cool down easily
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36
Q

What is the importance of the high specific heat capacity of water to living organisms?

A
  • Living things need a stable temperature for enzyme-controlled reactions to happen properly
  • Aquatic organisms need a stable environment in which to live
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37
Q

Why does water have a high latent heat of vaporisation?

A

Because the water molecules are held together by hydrogen bonds, a relatively large amount of energy is needed for water molecules to evaporate

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38
Q

What is the importance of the high latent head of vaporisation of water to living organisms?

A

Water can help to cool living things and keep their temperature stable e.g.
* Mammals are cooled when sweat evaporates
* Plants are cooled when water evaporates from mesophyll cells

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39
Q

What is the importance of water’s role as a reactant to living organisms

A

It is a reactant in reactions such as photosynthesis, and in hydrolysis reactions such as digestion of starch, proteins and lipids
* Plays a very important role in the digestion and synthesis of large biological molecules

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40
Q

What are carbohydrates?

A

Organic polymers composed of the elements carbon, hydrogen and oxygen, usually in the ration Cx(H2O)y. Also known as saccharides or sugars

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41
Q

What is a monosaccharide?

A

A single sugar molecule e.g. glucose, fructose and ribose

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42
Q

What is a disaccharide?

A

A molecule comprising two monosaccharides joined together by a glycosidic bond

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43
Q

Describe glucose

A
  • C6H12O6
  • Hexose monosaccharide (because it has 6 carbons)
  • Polar and soluble in water due to the hydrogen bonds that form between the OH group and water molecules
  • Means glucose is dissolved in the cytosol of the cell
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44
Q

What are the 2 variations of glucose?

A

*⍺ glucose - OH group is below carbon 1
*ß glucose - OH group is above carbon 1

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45
Q

How do alpha glucose molecules react with each other?

A
  • The OH groups on C1 and C4 reacted forming a 1,4 glycosidic bond (covalent)
  • Condensation reaction because a water molecule is formed (lost)
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46
Q

What do the following combinations form?
1. a-glucose + a-glucose
2. a-glucose + fructose
3. B-galactose + a-glucose
4. B-glucose+ B-glucose

A
  1. Maltose
  2. Sucrose
  3. Lactose
  4. Cellobiose
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47
Q

What are pentose monosaccharides? Give examples

A
  • Sugars that contain 5 carbon atoms
  • e.g. ribose which is the sugar present in RNA nucleotides
  • e.g. deoxyribose which is the sugar present in DNA nucleotides
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48
Q

What is starch?

A

A polysaccharide formed from alpha glucose molecules either joined to form amylose or amylopectin. Found in plants

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49
Q

Describe amylose

A
  • Found in plants
  • Alpha glucose
  • Glycosidic bonds between C1 and C4
  • Coils into a spiral shape held together by hydrogen bonds
  • OH groups on C2 inside of the coil, making the molecule less soluble and allowing hydrogen bonds to form to maintain the coil’s structure
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50
Q

Describe amylopectin

A
  • Found in plants
  • Alpha glucose
  • Has glycosidic bonds between C1 and C4, and also has branches formed by glycosidic bonds between C1 and C6
  • Coils into a spiral shape held together by hydrogen bonds, but with branches coming out of the spiral
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51
Q

What is glycogen?

A

A branched polysaccharide formed from ⍺ glucose

A chemical energy store in animals

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52
Q

Describe glycogen

A
  • Found in animals
  • Like amylopectin with glycosidic bonds between C1 and C4, and branches formed by glycosidic bonds between C1 and C6
  • The C1 C4 bonded chains are smaller than in amylopectin so glycogen has less tendency to coil
  • Has more branches than amylopectin making it more compact
  • Easier to remove monomer units as there are more ends
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53
Q

How do beta-glucose molecules react with each other?

A
  • The OH groups on C1 and C4 are to far away to react, so each alternate beta glucose molecule must be turned upside down to reach
  • It is unable to could or form branches
  • A straight chain molecule called cellulose is formed
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54
Q

Describe cellulose

A
  • Cellulose molecules make hydrogen bonds with each other forming microfibrils
  • Microfibrils join together to form macrofibrils that combine to produce fibres
  • The fibres are strong and insoluble and are used to make cell walls
55
Q

Why is cellulose a good material for cell walls?

A
  • Microfibrils and macrofibrils have very high tensile strength because of the glycosidic bonds and hydrogen bonds
  • macrofibrils run in all directions, criss-crossing the wall for extra strength
  • Space between macrofibrils for water and mineral ions to pass in and out of the cell, making the cell wall full permeable
56
Q

What are lipids?

A

Non-polar macromolecules contains the elements carbon, hydrogen and oxygen. Soluble in alcohol rather than water. Include triglycerides, phospholipids and sterols.

57
Q

What are triglycerides?

A

Lipids composed of one glycerol (C3H8O3) molecule and three fatty acids. Fatty acids are carboxylic acids that consist of a carboxyl group (-COOH) which a hydrocarbon chain attached.

58
Q

How are triglycerides formed?

A
  • The hydroxyl groups in the fatty acid molecule and glycerol molecule react
  • This leads to the formation of 3 water molecules and bonds between the fatty acid and glycerol molecule
  • The bonds are called ester bonds, and the reaction is called esterification
  • Esterification is an example of a condensation reaction
59
Q

What is the difference between saturated and unsaturated triglycerides?

A
  • Fatty acid chains that have no double bonds between the carbon atoms are saturated, and vice versa
  • If there’s 1 double bond = monounsaturated
  • If there’s 2 or more double bonds = polyunsaturated
60
Q

How does the presence of double bonds in unsaturated triglycerides cause?

A
  • Changes the bond angle and causes the molecule to kink or bend
  • Therefore the molecules cannot pack so closely together
  • Makes them liquid at rtp rather than solid, so they are oils rather than fats
61
Q

What type of triglycerides do plants contain?

A

Unsaturated triglycerides, which normally occur as oils

62
Q

Which type of triglycerides are healthier?

A

Unsaturated triglycerides are healthier for human than triglycerides or (solid) fats.

63
Q

What are phospholipids?

A

Modified triglycerides, where one fatty acid has been replaced with a phosphate group. They are found in the cytoplasm of very cell.

64
Q

What are the characteristics of phospholipids?

A
  • Have a non-polar end (the fatty acid chains) which are hydrophobic and repelled by water
  • Have a charged head (the phosphate PO43-) which are hydrophilic and attracted to water
65
Q

How do phospholipids interact with water?

A
  • Form a layer on surface of water with phosphate heads (hydrophilic) in the water and fatty acid tails (hydrophobic) sticking out
  • Can form structures based n a bilayer with all the hydrophobic tails pointing towards the centre of the sheet, protected by from the water by hydrophilic heads
66
Q

How do the characteristics of phospholipids help in the formation of cell membranes?

A

The bilayer arrangement means that they can separate the aqueous environment in which cells usually exist, from the aqueous cytosol within the cells

67
Q

What are sterols?

A

Steroid alcohols. Complex alcohol molecules based on a 4 carbon ring structure with a hydroxyl (OH) group at one end.

68
Q

Describe the characteristics of sterols

A

Have a dual hydrophilic/hydrophobic characteristics. The hydroxyl group is polar and therefore hydrophilic, and the rest of the molecule is hydrophobic.

69
Q

What is cholesterol?

A
  • A type of sterol
  • The body primarily manufactures it in the liver and intestines
  • Vitamin D, steroid hormones and bile are all manufactured using cholesterol
70
Q

What is the importance of cholesterol in the formation of cell membranes?

A
  • Positioned between the phospholipids with the hydroxyl group at the periphery of the membrane
  • Adds to the stability of cell membranes
71
Q

What is the importance of cholesterol in regulating the fluidity of cell membranes?

A

Keeps membranes fluid at low temperatures and stops them becoming too fluid at high temperatures

72
Q

What are the roles of lipids? (Due to their non-polar nature) (4)

A
  • Membrane formation and the creation of hydrophobic barriers
  • Hormone production
  • Electrical insulation necessary for impulse transmission
  • Waterproofing, e.g. in birds’ feathers and on plant leaves
73
Q

What are the roles of triglycerides in particular?

A
  • Long-term energy storage

Stored under the skin and around vital organs where they provide:
* Thermal insulation to reduce heat loss, e.g. in penguins
* Cushioning to protect vital organs e.g. heart and kidneys
* Buoyancy for aquatic animals like whales

74
Q

Define the following:
1. Proteins
2. Peptides
3. Peptide bond
4. Amino acid

A
  1. One or more polypeptides arranged as a complex macromolecule
  2. Chains of two or more amino acid molecules
  3. Bond formed between two amino acids
  4. Monomer used to build polypeptides and thus proteins
75
Q

Describe what happens when two amino acids react together

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 produced (condensation reaction)
  • The resulting compound is a dipeptide
76
Q

When is a polypeptide formed?

A
  • When many amino acids are joined together by peptide bonds
  • This reaction is catalysed by the enzyme peptide transferase present in ribosomes, the sites of protein synthesis
77
Q

What happens to the R-groups of the amino acids when the amino acids react?

A
  • Different R-groups interact with each other (R-group interactions) forming different types of bond
  • These bonds lead to polypeptides folding into complex structures (proteins)
78
Q

What does the presence of different sequences of amino acids lead to?

A

Different structures with different shapes being produced

The very specific shapes of proteins are vital for the many functions proteins have within living organisms

79
Q

What is the primary structure of proteins?

A
  • The sequence in which the amino acids are joined
  • Directed by information carried within DNA
  • The amino acids in the sequence will influence how the polypeptide’s fold to give the proteins final shape, and determine its function
  • The only bonds here are peptide bonds
80
Q

What is the secondary structure of proteins?

A
  • The oxygen, hydrogen, and nitrogen atoms of the amino acids (excluding R groups) interact
  • A result of hydrogen bonds and forms at regions along long protein molecules depending on the amino sequences
81
Q

What are the two types of secondary structure?

A
  • Alpha Helix - Hydrogen bonds form within the amino acid chain, pulling it into a coil shape called an alpha-helix
  • Beta Pleated Sheet- Polypeptide bonds lie parallel to each other joined by hydrogen bonds, forming sheet-like structures.The pattern formed by individual amino acids makes the structure appear pleated
82
Q

What is tertiary structure?

A
  • The folding of a protein into its final shape
  • Often includes sections of secondary structure
  • The coiling or folding of sections of proteins into their secondary structures brings R-groups of different amino acids closer together so they can interact
83
Q

List the interactions that occur between R-groups (4)

A
  • Hydrophobic and hydrophilic interactions - weak interactions between polar and non-polar R-groups
  • Hydrogen bonds - these are the weakest of bonds formed
  • Ionic bonds - stronger than hydrogen bonds and form between oppositely charged R-groups
  • Disulfide bonds/bridges - covalent and the strongest of the bonds but only form between R-groups that contain sulphur atoms
84
Q

What is quaternary structure?

A
  • Protein structure where a protein consists of more than 1 polypeptide chain, e.g insulin has a quaternary structure
  • Results from the association of 2 or more individual proteins called subunits
  • The interaction between subunits are the same as in tertiary structure except between different protein molecules rather than within one molecule
  • The protein subunits can be identical or different
85
Q

Describe hydrophilic and hydrophobic interactions in proteins

A
  • Proteins are assembled in the aqueous environment of the cytoplasm
  • The way a protein will fold also depends on whether the R-groups are hydrophilic or hydrophobic
  • Hydrophilic groups arena the outside, whilst hydrophobic are on the inside of the molecule (away from the cytoplasm)
86
Q

List the types of proteins (3)

A
  • Globular proteins
  • Conjugated proteins
  • Fibrous proteins
87
Q

What are globular proteins?

A

Compact, spherical, water-soluble proteins
* Form when proteins fold into their tertiary structures so that the hydrophobic R-groups on the amino acid are kept away from the aqueous environment
* Hydrophilic R-groups on the outside of the protein meaning the proteins are soluble in water
* e.g. Insulin

88
Q

Describe how the structure of Insulin is suited to its function

A

**Globular protein **
* Hormone involved in regulation of blood glucose concentration
* Hormones are transported in the bloodstream so need to soluble
* Hormones have to fit into specific receptor on cell-surface membranes to work, therefore need to have precise shapes

89
Q

What are conjugated proteins?

A

Globular proteins that contain a prosthetic group

Lipids or carbohydrates can combine with proteins forming lipoproteins or glycoproteins. Metal ions and molecules derived from vitamins also form prosthetic groups

  • e.g. Haemoglobin and Catalase both contain prosthetic harm groups (Fe2+)
90
Q

Describe how the structure of haemoglobin makes it suited to its function

A
  • Red, oxygen-carrying pigment in red blood cells
  • Quaternary protein made from 4 polypeptides (2 alpha and 2 beta subunits)
  • Each subunit contains a prosthetic hem group
  • The Fe2+ ions in the haem groups are each able to combine reversibly with an oxygen molecule which enables haemoglobin to transport oxygen around the body
91
Q

Describe how the structure of catalase makes it suited to its function

A
  • An enzyme
  • A quaternary protein containing 4 prosthetic harm groups
  • The presence of Fe2+ ions in the haem groups allow catalase to interact with hydrogen peroxide and speed up its breakdown
  • Hydrogen peroxide is a common byproduct of metabolism but damaging to cells and cell components, so catalase makes sure it doesn’t accumulate
92
Q

What are fibrous proteins?

A

Long insoluble, structural proteins

  • Due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structures
  • Amino acid sequence in primary structure is usually very repetitive leading to very organised structures
  • Are NOT folded into complex 3D shapes like globular proteins
  • E.g. Keratin, Elastin and Collagen
93
Q

Describe how the structure of keratin is suited to its function

A
  • Group of fibrous proteins presenting hair, skin and nails
  • Large proportion of the sulfur-containing amino acid cysteine leading to many strong disulphide bonds forming strong, inflexible, insoluble materials
  • Hair contains fewer disulphide bonds than nails, so is more flexible
94
Q

Describe how the structure of elastin is suited to its function

A
  • Fibrous protein found in elastic fibres
  • Elastic fibres are present in the walls of blood vessels and in the alveoli of the lungs
  • Give these structures flexibility to expand when needed but also to return to their normal size
  • Quaternary protein made from many stretch molecules called tropoelastin
95
Q

Describe how the structure of collagen makes it suited to its function

A
  • Fibrous protein
  • Connective tissue found in skin, tendons, ligaments and the nervous systems
  • Many different forms but all are made up of 3 polypeptides wound together in a long and strong rope-like structure
  • Like rope, collagen has flexibility
96
Q

Describe the test for starch

A
  1. Add iodine solution (in potassium iodide) to a sample
  2. If starch is present, you will see a colour change from yellow-brown to blueback
  • When dissolved in potassium iodide, the iodine (I2) forms a triiodide I3-, which slips into the middle of the amylose helix, causing a colour change
97
Q

Describe the test for reducing sugars (all monosaccharides and some disaccharides)

A
  1. Place the sample in a boiling tube. If its not liquid, grind it up or lend it in water
  2. Add an equal volume fo Benedict’s solution
  3. Heat the mixture gently in a boiling water bath for 5 minutes

Blue > Green > Yellow > Orange > Red

  • Benedict’s reagent is an alkaline solution of copper (II) sulphate
  • The more reducing sugar present, the more brick-red precipitate formed and the less blue Cu2+ ions left in solution
98
Q

Describe the test for non-reducing sugars

A
  1. Do Benedict’s test for reducing sugars, the result will be negative
  2. Sucrose is the most common non-reducing sugar
  3. If sucrose is first boiled with dilute hydrochloric acid then it’ll give a positive result when warmed with Benedict’s solution
  • This is because the sucrose has been hydrolysed by the acid to glucose and fructose, both reducing sugars
99
Q

Describe the test for lipids

A
  1. Mix the sample with ethanol
  2. The resulting solution is mixed with water and shaken
  3. If a white emulsion forms as a layer on top the solution, this indicated the presence of a lipid
  4. If the solution remains clear, the test is negative
100
Q

Describe the test for proteins

A
  1. Add Biuret A (sodium hydroxide) and then Biuret B (copper sulphate) to the sample
  2. If a protein is present, the colour changes from light blue to lilac/ mauve
101
Q

What are nucleic acids?

A

Large polymers formed from nucleotides. Contain the elements carbon, nitrogen, hydrogen, phosphorus, and oxygen.

102
Q

Describe the composition of nucleotides

A
  • A pentose monosaccharide containing 5 carbon atoms
  • A phosphate group, (PO42-) and inorganic molecule that is acidic and negatively charged
  • A nitrogenous base - a complex organic molecule containing 1 or 2 carbon rings in its structure, as well as nitrogen
103
Q

How do nucleotides link together to form a polynucleotide?

A
  • By condensation reactions
  • Phosphate group at the 5th carbon of the pentose sugar (5’) of one nucleotide forms a covalent bond with the hydroxyl (OH) group at the 3rd carbon (3’) of the pentose sugar of another nucleotide
  • These bonds are called phosphodiester bonds
  • Forms a long, strong sugar-phosphate ‘backbone’
  • Phosphodiester bonds are broken by hydrolysis
104
Q

What is Deoxyribonucleic acid (DNA) ?

A

** The molecule responsible for the storage of genetic information **
* The sugar is deoxyribose, which has 1 less oxygen atoms than a ribose sugar
* The nucleotides each have 1 of 4 different bases: Adenide, Thymine, Guanine, or Cytosine

105
Q

What are pyrimidines?

A
  • Single-ringed, nitrogenous bases that form part of a nucleotide
  • Smaller bases
  • Thymine (T) and Cytosine (C)
106
Q

What are purines?

A
  • Double-ringed, nitrogenous bases that form part of a nucleotide
  • Larger bases
  • Adenine (A) and Guanine (G)
107
Q

Describe the double helix structure of DNA

A
  • Made up of 2 strands of polynucleotides coiled into a helix
  • The 2 strands are 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 2 parallel strands run in opposite directions - antiparallel
108
Q

What is complementary base pairing?

A

Specific hydrogen bonding between nucleic acid bases. A binds to T or U, C binds to G

  • A and T form 2 hydrogen bonds so always join with each other
  • C and G form 3 hydrogen bonds so always join with each other
109
Q

What are the consequences of complimentary base pairing?

A
  • A small pyrimidine base always binds to a larger purine base; this arrangement keeps a constant distance between the DNA backbones, resulting in parallel polynucleotide chains
  • DNA always has equal amounts of adenine and thymine, and cytosine and guanine
110
Q

What is Ribonucleic acid? (RNA)

A

Polynucleotide molecules involved in the copying and transfer of genetic information from DNA.

The monomers are nucleotides consisting of a ribose sugar and 1 of four bases: Adenine, Uracil, Cytosine, or Guanine

111
Q

What are the similarities and differences between DNA and RNA?

A

Similarities:
* RNA nucleotides form polymers in the same way as DNA nucleotides - by the formation of phosphodiester bonds

Differences:
* In RNA the pentose sugar is ribose, meanwhile in DNA it’s deoxyribose
* In RNA, the thymine base is replaced with Uracil

112
Q

What is DNA replication?

A

The semi-conservative process of the production of identical copies of DNA molecules

113
Q

What is semi-conservative replication?

A

DNA replication results in one old strand and one new strand present in each daughter DNA molecules

114
Q

Describe the process of semi-conservative replication

A
  1. The enzyme DNA helicase travels along the DNA backbone, catalysing reactions that breaks the hydrogen bonds between complimentary base pairs
  2. After the ‘unzipping’, free DNA nucleotides will then pair with their complimentary bases, which have been exposed as the strands separate
  3. Hydrogen bonds are formed between the new complimentary bases
  4. The enzyme DNA polymerase catalyses the formation of phosphodiester bonds between adjacent new nucleotides
115
Q

What is a mutation?

A

A change in the genetic material which may affect the phenotype of the organism.

Happen due to random error in the replication of DNA that lead to a change in the sequence of bases

116
Q

What is the genetic code?

A

The sequences of baes in DNA are the ‘instructions’ for the sequences of amino acids in the production of proteins

117
Q

What is a triplet code?

A

The genetic code is a sequence of three nucleic acids bases, called a codon. Each codon codes for one amino acids.

A section of DNA that contains the complete sequence of baes (codons) to ode for an entire protein is called a gene.

118
Q

Why is the genetic code a degenerate code?

A
  • There are 64 different base triplets or codons possible, but there are only 20 amino acids
  • Therefore, many amino acids can be coded for by more than one codon
119
Q

How are genes read?

A
  • There’s a start codon (ATG) that signals the start of a sequence that codes for a protein (if it’s in the middle of a gene it codes for methionine)
  • Having a start codon means that codons are read ‘in frame’, so the genetic code is non-overlapping
  • There are 3 stop codons that don’t code for any amino acids, and signal the end of the sequence
120
Q

What is transcription?

A

The process of copying smaller sections of DNA base sequence to produce smaller molecules of mRNA, which can be transported out of the nucleus via the nuclear pores, to the site of protein synthesis

121
Q

Describe the process of transcription

A
  1. A gene unwinds and unzips, aided by DNA helicase, and the hydrogen bonds between complimentary nucleotide bases break
  2. The sense strand (5’ to 3’) codes for the protein, whilst the antisense strand (3’ to 5’)acts as the template strand during transcription
  3. RNA polymerase catalyses the formation of temporary hydrogen bonds between RNA nucleotides and their complimentary DNA bases on the template strand
  4. The strand of RNA produced is complimentary to the template strand, so is a copy of the sense/ coding strand
  5. Messenger RNA (mRNA) passes out of the nucleus, through the nuclear envelope, whilst the DNA double helix reforms
122
Q

What are ribosomes made up of? (eukaryotic cells)

A
  • 2 subunits, one large and one small
  • Almost equal amounts of protein and ribosomal RNA (rRNA)
123
Q

What is the role of rRNA?

A
  • Maintaining the structural stability of the protein synthesis sequence
  • Biochemical role in catalysing the reaction
124
Q

What happens to mRNA after it has left the nucleus?

A
  • Binds to a specific site on the small subunit of a ribosome
  • The ribosome holds mRNA in position while it is translated into a sequence of amino acids
  • This process is called translation
125
Q

What is translation?

A

The process by which the complementary code carried by mRNA is decoded by tRNA into sequence of amino acids. This occurs at a ribosome

126
Q

What is transfer RNA (tRNA)?

A

Form of RNA that carries an amino acid specific to its anticodon to the correct position along mRNA during translation

  • Single stranded polynucleotides, but can twist into a hairpin shape
  • At one end is a trio of nucleotide bases that recognises and attaches to a specific amino acid
  • At the loop is another triplet of bases called an anticodon that is complementary to a specific codon of bases on the mRNA
127
Q

Describe how translation happens at a ribosome

A
  1. mRNA binds to the small subunit of the ribosome at its start codon (AUG)
  2. A tRNA with the complementary anticodon (UAC) binds to the mRNA start codon. This tRNA carries the amino acid methionine
  3. Another tRNA with the complementary anticodon, and carrying an amino acid, binds to the next codon on the mRNA. A maximum of 2 tRNAs can be bound at the same time
  4. The 1st amino acid (methionine) is transferred to the amino acid on the 2nd tRNA by the formation of a peptide bond. This is catalysed by the enzyme peptidyl transferase, which is an rRNA component of the ribosome
  5. The ribosome then moves along the mRNA, releasing the 1st tRNA. The 2nd tRNA becomes the 1st
  6. Stages 3-5 are repeated until the ribosome reaches the end of the mRNA at a stop codon, and the polypeptide is released
128
Q

What is ATP?

A

Adenosine triphosphate

A nucleotide composed of a nitrogenous adenine base, a pentose sugar, and 3 phosphate groups. The ‘universal energy currency’ for cells, because it is used for energy transfer in all cells.

129
Q

What are the 3 main types of activity cells require energy for?

A
  • Synthesis - e.g. of large molecules such as proteins
  • Transport - e.g. pumping molecules or ions across cell membranes by active transport
  • Movement - e.g. protein fibres in muscle cells that cause muscle contraction
130
Q

What is ADP?

A

Adenosine diphosphate

A nucleotide composed of a nitrogenous adenine base, a pentose sugar and 2 phosphate groups

Formed by the hydrolysis of ATP, releasing a phosphate ion and energy

131
Q

Why is ATP not a good long-term energy store? (4)

A
  • The instability of the phosphate bonds
  • Fats and carbohydrates are better long-term energy stores
  • Energy released in the breakdown of these molecules (a process called cellular respiration) is used to create ATP
  • A phosphate group is reattached to an ADP molecule (phosphorylation which is an example of a condensation reaction)
132
Q

Why do cells not store large amounts of ATP? (4)

A
  • Due to the instability of ATP
  • Instead ATP is rapidly reformed by the phosphorylation of ADP
  • Interconversion of ATP and ADP is happening constantly in all living cells, so cells don’t need a large store of ATP
  • ATPis a good immediate energy store
133
Q

How does ATP carry energy?

A
  1. When a cell needs energy, ATP is broken down to ADP and Pi
  2. In the hydrolysis reaction, a phosphate bond is broken and energy released to be catalysed by the enzyme ATP hydrolase
  3. ATP hydrolysis can be couple to other reactions in the cell - the energy can be used directly to make the coupled reaction happen (instead of being lost as heat)
  4. The released phosphate can be added to another compound (phosphorylation) which often makes the compound more reactive
  5. ATP can be re-synthesised in a condensation reaction between ADP and Pi. The enzyme ATP synthase catalyses it during both respiration and photosynthesis
134
Q

What are the properties of ATP that make it suited to carry out its function in energy transfer?

A
  • Small - moves easily into, out of, and within cells
  • Water soluble - energy requiring processes happen in aqueous environments
  • Contains bonds between phosphates with immediate energy: large enough to be useful for cellular reactions, but not so large that energy is wasted as heat
  • Releases energy in small quantities - quantities are suitable to most cellular needs, so that energy is not wasted as heat
  • Easily regenerated - can be recharged with energy

AS Biology (5 decks)

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