Biological Molecules Flashcards
1
Q
What are different types of atoms called?
A
Elements.
2
Q
What are the four key elements?
A
Carbon, hydrogen, oxygen and nitrogen.
3
Q
Other than carbon, hydrogen, oxygen and nitrogen, name two more key elements in biochemistry.
A
Phosphorus and sulfur.
4
Q
What is the name given when two or more atoms bond together?
A
A molecule.
5
Q
How many bonds can carbon atoms form?
A
Four bonds.
6
Q
How many bonds can nitrogen atoms form?
A
Three bonds.
7
Q
How many bonds can oxygen atoms form?
A
Two bonds.
8
Q
How many bonds can hydrogen atoms form?
A
One bond.
9
Q
What is the name given to ions in solution?
A
Electrolytes.
10
Q
Which elements do carbohydrates contain?
A
Carbon, hydrogen and oxygen.
11
Q
What ratio of elements are often found in carbohydrates?
A
Cn(H2O)n
12
Q
Which elements do lipids contain?
A
Carbon, hydrogen and oxygen
13
Q
Which elements do proteins contain?
A
Carbon, hydrogen, oxygen, nitrogen and sulfur.
14
Q
Which elements do nucleic acids contain?
A
Carbon, hydrogen, oxygen, nitrogen and phosphorus.
15
Q
Explain the slight charges in polar molecules.
A
In many covalent bonds, the electrons will spend more time closer to one of the atoms than to the other. The atoms with the greater share of negative electrons will be slightly negative compared with the other atom in the bond which will therefore be slightly positive.
16
Q
Describe the way in which oxygen and hydrogen share electrons in a covalent bond.
A
Oxygen has a much greater share of the electrons in an O—H bond. Organic molecules that contain an OH group are slightly polar.
17
Q
How do polar molecules interact with one another?
A
The positive and negative regions of the molecule attract each other and from bonds called hydrogen bonds.
18
Q
True or false, hydrogen bonds are weak interactions which break and reform between the constantly moving water molecules.
A
True
19
Q
Explain why water has an unusually high boiling point.
A
The hydrogen bonding between molecules is responsible. It takes a lot of energy to increase the temperature of water and cause water to become gaseous.
20
Q
Explain why when water turns to ice, it becomes less dense.
A
As water is cooled below 4 degrees 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, with every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms.
21
Q
Why does water have cohesive properties? Give an example of where this is important.
A
It moves as one mass because the molecules are attracted to each other. Plants can draw water up their roots as a result of this.
22
Q
Explain what is meant by water having adhesive properties.
A
This is where water molecules are attracted to other materials.
23
Q
What is meant by surface tension in relation to water?
A
Water molecules are more strongly cohesive to each other than they are to the air which results in a ‘skin’ of surface tension.
24
Q
What is meant by the term ‘capillary action’?
A
This is the process by which water can rise up a narrow tube against the force of gravity due to adhesion and cohesion.
25
What is the significance for life of water having low viscosity?
Water is able to flow easily through very small spaces.
26
What is the significance for life of water remaining liquid over a wide temperature range?
It provides a liquid medium for aquatic life and for inside cells.
27
What is the significance for life of water being colourless with a high transmission of visible light?
Light is able to penetrate tissue and aquatic environments.
28
What is the significance for life of water having the property of cohesion?
It makes it an excellent transport medium. Water is not easily compressed so it provides good support.
29
What is the significance for life of water being a good solvent for other polar species?
All reactions of metabolism occur in water and water is one of the main transport mediums in organisms.
30
What is the significance for life of water having high latent heat of fusion?
Significant amounts of energy are required before water will change state meaning cell contents are unlikely to freeze.
31
What is the significance for life of water having high latent heat of vaporisation?
Water must absorb a large amount of energy in order to evaporate. Heat is easily lost by evaporation. Sweating in animals and transpiration in plants causes rapid cooling.
32
What is the significance for life of water having high specific heat capacity?
Water can absorb a lot of energy for only a small rise in temperature. Aquatic environments are thermally stable. Organisms can maintain stable internal temperatures despite fluctuations in external temperature.
33
What is the name given to the monomers in carbohydrates?
Monosaccharides
34
What is the name given to the monomers in proteins (polypeptides)?
Amino acids
35
What is the name given to the monomers in RNA/DNA?
Nucleotides
36
What are the two components that make up lipids?
Glycerol and fatty acids
37
What are polymers?
Polymers are large complex molecules composed of long chains of monomers joined together.
38
What are monomers?
Monomers are small, basic molecular units that can form a polymer.
39
What type of reaction builds up polymers from monomers?
Condensation reaction.
40
What is released as a product of condensation reactions?
A molecule of water.
41
What type of reaction breaks down polymers in to their individual monomers?
Hydrolysis reactions.
42
What does hydrolysis mean?
Hydrolysis means splitting up with water.
43
Where is the energy supplied from in order to join monomers to form disaccharides and polysaccharides?
Energy is supplied by a nucleotide sugar such as ADP-glucose.
44
In a hydrolysis reaction, what does the water molecule provide?
It provides the hydrogen and hydroxyl groups.
45
What can hydrolysis reactions be catalysed by?
Enzymes.
46
Give two important roles of carbohydrates.
Carbohydrates are important as energy storage molecules and as the structural elements in cells and tissues.
47
What are monosaccharides? How are they classified?
Single sugar units, classified according to the number of carbon atoms that they contain.
48
What is the name of this monosaccharide?
Hexose (glucose)
49
True or false? Monosaccharides can be joined together in enzyme controlled reactions to form disaccharides and polysaccharides.
True
50
What are disaccharides?
Two monosaccharides bonded together
51
Is this a monosaccharide, disaccharide or a polysaccharide? How do you know?
Disaccharide because it contains two monosaccharides joined together.
52
Explain what is meant by the term isomer.
Compounds that have the same chemical formula but a different arrangement of atoms
53
True or false? Glucose only has one ring-structural isomer.
False. It has two; alpha glucose and beta glucose
54
Is this a (alpha) glucose or ß (beta) gluccose? How do you know?
Alpha because the hydrogen attached to C1 is above carbon.
55
Describe the difference in structure between an alpha and a beta glucose.
Alpha glucose has the hydrogen atom bonded to C1 above it whereas beta glucose has it below.
56
True or false? Both structural isomers of glucose have the same molecular formula of C6H12O6.
True
57
What does the reaction in the picture show?
Condensation reaction
58
Explain the process of condensation reactions and hydrolysis reactions of two alpha glucose molecules including what type of glycosidic bonds form.
* two a-glucose molecules (C1 and C4) meet
* OH groups from C1 and the H from C4 react
* water is expelled
* this can be reversed by adding water
* the OH and H groups separate back out again.
59
Fill in the blanks. Starch is a ______ of glucose, made up of long ______ of ______ molecules. Starch is made up of ______ and \_\_\_\_\_\_
polymer, chains, a-glucose, amlose, amylopectin
60
Describe the structure of amylose.
Amylose- long unbranched chains of many hundreds of a-glucose linked by 1-4 glycosidic bonds. Forms a helix structure held together by intra molecular hydrogen bonds.
61
Describe the structure of amylopectin.
Amylopectin- branched chains of a-glucose with 1-6 glycosidic bonds every 23-30 glucose units.
62
Describe the role of starch and where it is found.
Starch is an energy store in plants found concentrated in insoluble starch granules within plant cells, seeds and tubers.
63
True or false? Starch can be easily hydrolysed to maltose by the enzyme amylase when required so glucose can be made available rapidly.
True
64
What are the benefits of starch being insoluble?
1. It won't diffuse out of the cell
2. It won't affect the water potential of a cell
65
Describe the structure of cellulose.
Cellulose- a polymer of B-glucose linked together by 1-4 glycosidic bonds. Every second molecule is flipped 180° to allow C1 and C4 to react.
66
Why is cellulose mechanically very strong?
Cellulose is mechanically very strong due to intermolecular hydrogen bonds between chains. Hundreds of these chains are linked together by hydrogen bonds to form cellulose microfibrils
67
Describe the structure of glycogen.
Extensively branched a-glucose molecules with 1,4 and 1,6 glycosidic links.
68
Why is glycogen mostly found in liver and muscle cells?
Because they are both centres of high metabolic activity.
69
Why is it a good thing that amylopectin and glycogen are branched?
Becauase it means that there are more ends that can liberate glucose monomers by hydrolysis.
70
Why are lipids suitable for storage?
Lipids are non-polar molecules and so are insoluble in water
71
Why are lipids a high energy store?
They have a high proportion of H atoms relative to O atoms and so yield more energy than the same mass of carbohydrates.
72
Why are fats suitable for thermal insulation?
Fat conducts heat very slowly so having a layer under the skin keeps metabolic heat in.
73
Why are fats suitable for waterproofing?
Waxy cuticles are useful to prevent excess evaporation from the surface of a leaf.
74
Why are lipids suitable for buoyancy?
Lipids float on water so can have a role in maintaining buoyancy in organisms.
75
True or false? One function of lipids is an energy store in seeds.
True
76
How can lipids exist? (three forms)
Waxes, fats or oils
77
What is this picture showing?
A triglyceride
78
What is the function of triglycerides?
Mainly used as energy storage molecules.
79
Where in a cell would you find phospholipids?
In membranes
80
Describe the molecular structure of lipids.
A glyceride molecule bonded to three fatty acid molecules
81
What is the general structure of a fatty acid?
82
What is the general structure of glycerol?
83
True or false? The long hydrocarbon tails of the fatty acids contain lots of chemical energy.
True.
84
Why do triglycerides form droplets inside cells?
The triglycerides bundle together as insoluble droplets in cells because the fatty actids tails are hydrophobic. The tails face inwards shielding themselves from water with their glycerol heads.
85
Fill in the blanks. Glycerol is a member of a group of molecules called \_\_\_\_\_\_. Fatty acids belong to a group of molecules called ______ acids.
Alcohols, carboxylic.
86
What do fatty acids consist of?
A carboxyl group (-COOH) with a hydrocarbon
87
Describe how a triglyceride molecule is formed.
Both the glycerol and fatty acid contain hydroxyl (OH) groups. These hydroxyl groups interact, leading to the formation of three water molecules and bonds between the fatty acids and the glycerol molecule.
88
What are the bonds called between the glycerol and fatty acid chains?
Ester link
89
What is the type of reaction where triglyceride molecules are formed?
Condensation
90
If the fatty acid chains within the lipid contain single carbon bonds only, is the lipid saturated or unsaturated?
Saturated
91
What is one general property of saturated lipids?
Solid at room temperature.
92
If one or more bonds between the carbon atoms are double bonds, is the lipid said to be saturated or unsaturated?
Unsaturated
93
What is a general property of unsaturated lipds?
Liquid at room temperature.
94
Why are unsaturated fatty acids more liquid at room temperature?
The chains are kinked and so do not pack closely together making them more fluid
95
Are fats solid or liquid at 20°C?
Solid.
96
Are oils solid or liquid at 20°C?
Liquid
97
True or false? The difference in the physical properties of fats and oils are as a result of the type of fatty acid attached to the glycerol molecule.
True.
98
What does polyunsaturated mean?
Many double bonds
99
True or false? Three separate condensation reactions are involved in producing a triglyceride. The process is called esterification.
True
100
What is the difference between the structure of triglycerides and phospholipids?
In phospholipids, one of the fatty acids is substituted by a phosphate group.
101
What are sterols?
A subgroup of the steroids
102
What type of structure are sterols based on?
Based upon the four-carbon ring structure and have both a hydrophilic end and a hydrophobic end.
103
Give three roles of lipids.
1. biological fuels
2. hormones
3. structural componants of membranes
104
What elements do polymers of amino acids contain?
C,H,N,O and sometimes S
105
What does the order of amino acids determine?
The order of amino acids determine the proteins structure and hence their function.
106
What is the sequence of amino acids determined by?
The sequence of amino acids is determined by base sequence found in DNA.
107
Give as many functions of proteins that you can think of.
* cell signalling
* enzymes
* respiration
* cell structure
* immune responses
* membrane bound transport
108
What is the general structure of an amino acid?
109
What is the H2N in an amino acid?
An amine group
110
What does the COOH (carboxyl group) do in an amino acid?
Makes the molecule behave like a weak acid.
111
What is the 'R' in the general structure of amino acids representitive of?
The 'R' group is a variable which means that it is different in each amino acid.
112
Describe the formation of dipeptides and polypeptides.
113
Give one location within the cell where you might find condensation reactions of amino acids.
In the ribosomes
114
Can a polypeptide chain contain several hundred amino acids?
Yes.
115
True or false? A polypeptide chain may be functional by itself or may need to be joined to other polypeptide chains to be functional.
True
116
What is the conformation a protein takes dependent upon? Why?
The conformation a protein takes is dependent upon the proteins amino acid structure. The R groups of each amino acid react and interact with eachother. These interactions determine the final conformation of the protein.
117
True or false? If the shape of a protein is altered then the protein may no longer be able to perform its biological role.
True
118
What are the four levels of protein structure? What does each one involve?
1. Primary (sequence of amino acids)
2. Secondary (shape of the polypeptide chain)
3. Tertiary (the way in which the proteins are folded)
4. Quaternary (the combination of chains)
119
What are the two common types of secondary structure?
Alpha helix coil and beta pleated sheets.
120
What are secondary structures the result of?
Secondary structures are the result of many hydrogen bond interactions between neighbouring CO and NH groups of the polypeptide backbone.
121
Are hydrogen bonds weak or strong individually?
They are weak individually.
122
What affects a proteins tertiary structure (the way it folds)?
Interactions between the 'R' groups or side chains on the amino acids.
123
Name five bonds (interactions) that you might find in a proteins tertiary structure.
Disulfide bonds, hydrogen bonds, hydrophobic interactions, hydrophilic interactions and ionic bonds.
124
Put the following bonds in order of strength from strongest to weakest. Disulfide bonds, hydrophilic interactions, hydrophobic interactions, hydrogen bonds and ionic bonds.
1. Disulfide bonds
2. Ionic bonds
3. Hydrophilic interactions
4. Hydrogen bonding
5. Hydrophobic reactions
125
What can disulfide bonds be broken by?
Strong reducing agents
126
What can hydrogen bonds be broken by?
pH extremes and very high temperatures.
127
What is another name for hydrophobic interactions?
Van de waals forces.
128
What can ionic bonds broken by?
pH extremes.
129
Where would you find disulfide bonds within a protein?
Between two cysteine amino acids.
130
Where would you find hydrogen bonds in a protein?
Between polar R-groups.
131
Where would you find hydrophobic interactions within a protein?
Between non-polar R-groups.
132
Where would you find hydrophilic interactions within a protein?
Between polar R-groups
133
Where would you find ionic bonds within a protein?
Between ionised amine and carboxylic groups.
134
True or false? Hydrophobic interactions are often found on the inside of the folds of proteins.
True.
135
What is a conjugated protein?
A conjugated protein is a globular protein with a prosthetic group
136
Describe the structure of haemoglobin.
Haemoglobin is a globular protein with four polypeptide chains, each with an associated haem group. Two identical alpha chains and two identical beta chains.
137
Why is haemoglobin highly soluble?
Hydrophilic R groups point into the molecule and hydrophobic R groups point out of the molecule.
138
How many oxygen atoms can each haemoglobin carry?
8.
139
Describe the structure of insulin.
Made of two polypeptide chains, two disulfide bridges and an internal disulfide bridge.
140
In insulin, how many amino acids does chain A and chain B have?
Chain A has 21 amino acids and chain B has 30 amino acids.
141
What type of protein is catalase?
A globular protein.
142
What is the role of catalase?
Catalase catalyzes the decomposition of hydrogen peroxide to water and oxygen which protects the cell from oxidative damage.
143
Describe the test for proteins including what a positive result looks like.
* add solutions to test tubes
* add water to another test tube as a control
* add biuret reagent A (sodium hydroxide solution)
* shake
* add biuret reagent B (copper sulfate solution)
* shake
* observe colour
* positive result = solution is purple
144
Describe the test for starch including what a positive result looks like.
* add solutions to test tubes
* add water to a separate test tube to act as a control
* add 5 drops of iodine solution to each test tube
* positive result = solution turns blue black
145
Describe the test for reducing sugars including what a positive result looks like.
* add solutions to test tubes
* add water to a separate test tube to act as a control
* and benedicts solution to each test tube
* place in a boiling water bath
* look to see if there is a colour change
* positive result = benedicts solution changes from blue to green to yellow to orange to red.
146
What is a reducing sugar?
A reducing sugar is any sugar that when in solution has an aldehyde or a ketone group.
147
Describe the test for non-reducing sugars.
* add solutions to test tubes
* add water to a separate test tube to act as a control
* add hydrochloric acid to each test tube
* put test tubes in to a water bath
* remove from water bath
* add solid sodium hydrogen carbonate
* add benedicts solution
* put test tubes in to a water bath
* remove
* look for colour change
* positive result = benedicts solution changes from blue to green to yellow to orange to red
148
Describe the test for lipids including what a positive result looks like.
* add solutions to test tubes
* add ethanol to each test tube
* add ethanol to a separate test tube to act as a control
* shake each test tube
* pour test tube in to a test tube of cold water
* positive result = a white emulsion forms
149
What is colourimetry?
Colourimetry is a method of measuring the amount of a substance in a solution.
150
How does colourimetry work?
A beam of light is passed through a sample of the solution. The machine then measures the amount of light passing through the solution or the amount of light absorbed.
151
In colourimetry, what is the amount of light passing through called?
the transmission of the solution.
152
In colourimetry, what is the amount of light absorbed called?
The absorbance of the solution
153
In colourimetry, what is absorbance proportional to?
The concentration of the solution
154
True or false? Colourimetry only works with colourless solutions?
False, it only works with coloured solutions.
155
What is thin layer chromatography?
Thin layer chromatography is a technique used to separate the individual components of a mixture.
156
What are the two phases of thin layer chromatography?
The mobile phase and the stationary phase.
157
Describe how thin layer chromatography works.
* a thin layer of silica gel is applied to a rigid surface
* amino acids are then added to one end of the gel
* this end is then submerged in organic solvent
* the organic solvent then moves through the silica gel
158
What does the rate at which the different amino acids in the organic solvent move through the silica gel depend upon?
It depends on the interactions (hydrogen bonds) they have with the silica in the stationary phase and their solubility in the mobile phase.
159
In thin layer chromatography, what is the mobile phase?
The mobile phase is the organic solvent moving through the silica gel.
160
In thin layer chromatography, why does the final result have dots at different places up the page?
Because the different amino acids can travel different distances in the same time period.
161
Which elements do nucleic acids contain?
Carbon, hydrogen, oxygen, nitrogen and phosphorus.
162
What is the name of the monomer that makes up a nucleic acid?
Nucleotides.
163
What is the structure of an individual nucleotide?
A pentose monosaccharide, a phosphate group and a nitrogenous base
164
What is the name of the type of reaction that joins nucleotides together to form a nucleic acid?
Condensation reactions
165
What is the name given to the bond whereby the fifth carbon of the pentose sugar forms a covalent bond with the hydroxyl group at the third carbon of the pentose sugar of an adjacent nucleotide?
Phosphodiester bonds
166
What do the phosphodiester bonds form?
A long, strong sugar-phosphate 'backbone' with a base attached to each sugar.
167
What does DNA stand for?
Deoxyribo nucleic acid
168
What is the difference in structure between deoxyribose and ribose?
Deoxyribose has a H group rather than an OH so has one less O than ribose.
169
How many different DNA nucleotides are there? Why?
Four different DNA nucleotides due to there being four different bases.
170
What are pyrimidines?
The two smaller bases which contain single carbon ring structures
171
What are purines?
The larger bases which contain double carbon ring structures
172
Name each base and whether it is a purine or a pyrimidine.
Thymine (T) = pyrimidine
Cytosine (C) = pyrimidine
Adenine (A) = purine
Guanine (G) = purine
173
True or false? Pyramidines always pair with purines.
True
174
Fill in the gaps. The complementary pair thymine and adenine form ______ hydrogen bonds and the complementary pair cytosine and guanine form ______ hydrogen bonds.
Two, three
175
What is a DNA double helix?
Two strands of polynucleotides coiled in to a helix
176
Describe how the two strands of the double helix are arranged.
The two strands of the double helix are held together by hydrogen bonds between the bases. Each strand has a phosphate group at one end and a hydroxyl group at the other end.
177
True or false? The two strands of DNA are antiparallel, meaning that they run in opposite directions.
True
178
Why is the pairing between the bases so important?
The pairing between bases allows DNA to be copied and transcribed- key properties required of the molecule of heredity.
179
A small pyrimidine base always binds to a larger purine base. What does this arrangement mean?
It maintains a constant distance between the DNA backbones resuting in parellel polynucleotide chains.
180
Complementary base pairing means that DNA always has......
.......equal amounts of adenine and thymine and equal amounts of cytosine and guanine
181
True or false? It is the sequence of bases along a DNA strand that carries the genetic information of an organism in the form of a code.
True
182
What does RNA stand for?
Ribonucleic acid
183
What is the role of RNA?
RNA plays an essential role in the transfer of genetic information from DNA to the proteins that make up the enzymes and tissues of the body
184
True of false? The DNA of each eukaryotic chromosome is a very long molecule that is able to leave the nucleus in order to supply the information directly to the sites of protein synthesis.
False
185
Fill the gaps. The relatively short section of the long DNA molecule corresponding to a single gene is transcribed into a similarly short ______ molecule which is able to \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Fill the gaps. The relatively short section of the long DNA molecule corresponding to a single gene is transcribed into a similarly short **mRNA** molecule which is able to **leave the nucleus in order to take part in protein synthesis.**
186
Give one difference between DNA nucleotides and RNA nucleotides.
The pentose sugar in RNA is ribose as oppose to in DNA where it is deoxyribose.
187
True or False? The four bases found in DNA are the same in RNA. Explain your answer.
False. The thymine (T) base is replaced by the base uracil (U)
188
Fill in the gaps. Uracil is a ________ that forms ______ hydrogn bonds with \_\_\_\_\_\_\_.
Pyramidine, two, adenine.
189
Describe the way that RNA nucleotides form polymers. Is it the same or different to the way that DNA nucleotides form polymers?
The RNA nucleotides form polymers in the same way as DNA nucleotides by the formation of phosphodiester bonds in condensation reactions.
190
What happens to RNA molecules after protein synthesis?
RNA molecules are degraded in the cytoplasm. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.
191
Briefly describe the process of DNA extraction.
* Grind a sample to break down cell walls
* Mix the smaple with detergent to break down the cell membranes
* Add salt to break hydrogen bonds between DNA and water molecules
* Add protease enzyme
* Add ethanol
* DNA will form a white precipitate
192
Why do cells divide?
For growth and repair of tissues.
193
What is DNA replication?
When the two strands of DNA double helix separate and each strand serves as a template for the creation of a new double stranded DNA molecule
194
Describe the process of semi-conservative replication.
* The double helix structure has to unwind and then separate into two strands so the hydrogen bonds holding the complementary bases together must be broken.
* Free DNA nucleotides will then pair with their complementary bases and hydrogen bonds are formed between them
* The new nucleotides join to their adjacent nucleotides with phosphodiester bonds
195
What is meant by the term semi-conservative replication?
Where two new molecules of DNA are produced. Each one consisting of one old strand of DNA and one new strand.
196
Which enzyme unwinds and separates the two strands of the DNA double helix?
DNA helicase.
197
How does DNA helicase carry out its role?
It travels along the DNA backbone catalysing reactions that break the hydrogen bonds between complementary base pairs as it reaches them.
198
What is the role of DNA polymerase?
It catalyses the formation of phosphodiester bonds between the free nucleotides.
199
Describe what is meant by replication errors, when they occur and what they can lead to.
Replication errors are where sequences of bases are matched incorrectly. It occurs randomly and spontaneously which can lead to a change in the sequence of bases, known as a mutation.
200
Fill in the gaps. Proteins are the foundation for the different physical and biochemical characteristics of living things. They are made up of a _______ of amino acids, folded into _______ structures. Therefore ______ must code for a _________ of amino acids. This is called the genetic \_\_\_\_\_\_.
sequence, complex, DNA, sequence, code.
201
What is a codon?
A codon is a triplet of bases that code for an amino acid.
202
What is a gene?
A section of DNA that contains the complete sequence of bases (codons) to code for an entire protein.
203
True or false? The genetic code is universal.
True
204
The genetic code is a ______ code
Triplet
205
How many different base triplets (codons) are there?
64
206
How many codons code for the start of a protein sequence?
One
207
How many stop codons are there?
Three
208
Why is it important to have only one start codon?
Having a single codon to signal the start of a sequence ensures that the codons are read in order. This means that the genetic code is non-overlapping.
209
Why can many amino acids be coded for by more than one codon?
There are only 20 amino acids that regularly occur. There are a lot more codons than amino acids, therefore, many amino acids can be coded for by more than one codon
210
What is meant by the term degenerate?
Many amino acids can be coded for by more than one codon
211
What is transcription?
Transcription is when the base sequences of genes have to be copied and transported to the site of protein synthesis
212
Although transcription results in a different polynucleotide, it has many similarities with DNA replication. Decribe some of these similarities.
The section of DNA that contains the gene unwinds and unzips under the control of a DNA helicase begining a start codon. This involves the breaking of hydrogen bonds between the bases.
213
What is the sense strand?
The sense strand is the strand of DNA that contains the code for the protein to be synthesised.
214
What is the antisense strand and what is its role?
The antisense strand is complementary to the sense strand and acts as the template strand during transcription so that the complementary RNA strand carries the same base sequence as the sense strand.
215
During transcription, what happens to the free RNA nucleotides?
Free RNA nucleotides will base pair with complementary bases exposed on the antisense strand when the DNA unzips.
216
What happens once transcription ends?
The mRNA detatches from the DNA template and leaves the nucleus through a nuclear pore. The DNA double helix reforms.
217
How many subunits are ribosomes made up of?
Two, one large and one small.
218
What are the subunits of ribosomes made up of?
Protein and (r)RNA
219
What is the function of (r)RNA
rRNA is important in maintaining the structural stability of the protein synthesis sequence and plays a biochemical role in catalysing the reaction
220
What is translation?
Translation is when the mRNA is decoded, or translated, into a sequence of amino acids
221
What is (t) RNA and what does it do?
tRNA is necessary for the translation of the mRNA. It is composed of a strand of RNA folded in a way so that there is the anticodon at one end of the molecule. This anticodon will bind to a complementary codon on mRNA following the normal base pairing rules. The tRNA molecules carry an amino acid corresponding to that codon.
222
Fill in the gaps. As the amino acids are joined together to form the _______ structure of the protein, they _____ into ________ and tertiary structures. This folding and the ______ that are formed are determined by the sequence of ______ \_\_\_\_\_\_\_ in the primary structure.
As the amino acids are joined together to form the **primary** structure of the protein, they **fold** into **secondary** and tertiary structures. This folding and the **bonds** that are formed are determined by the sequence of **amino acids** in the primary structure.
223
True or false? The protein may undergo further modifications at the Golgi apparatus before it is fully functional and ready to carry out the specific role for which it has been synthesised.
True
224
Name three processes in the body that require energy.
1. Muscle contraction
2. Cell division
3. Transmission of nerve impulses
4. Memory formation
225
What are the three main types of activity that cells require energy for? Give an example of each one
* SYNTHESIS- for example of large molecules such as proteins
* TRANSPORT- for example pumping molecules or ions across cell membrnes by active transport
* MOVEMENT- for example protein fibres in muscle cells that cause muscle contraction
226
What does ATP stand for?
Adenosine triphosphate
227
Describe the structure of an ATP molecule.
An ATP molecule is composed of a nitrogenous base, a pentose sugar and three phosphate groups. It is a nucleotide.
228
Why is ATP known as the universal energy currency?
Because ATP is used for energy transfer in all cells of all living things.
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How does ATP release energy?
Energy is needed to break bonds and is released when bonds are formed. A small amount of energy is needed to break the weak bond holding the last phosphate group in ATP. However, a large amount of energy is then released when the liberated phosphate undergoes other reactions involving bond formation.
230
Overall, a lot more energy is released by ATP than is used. Approximately how much?
30.6KJmol-1
231
Here is the reaction for the removal of the phosphate group from an ATP molecule. What type of reaction is it? How do you know?
Hydrolysis. A molecule of water is needed to split up the ATP.
232
Why are the reactions involving ATP said to be 'coupled'?
The hydrolysis of ATP does not happen in isolation but in association with energy-requiring reactions. They happen simultaneously.
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What is ATP hydrolysed into?
ATP is hydrolysed into adenosine diphosphate (ADP) and a phosphate ion, releasing energy.
234
Why is ATP not a good long term energy store?
Due to the instability of the phosphate bonds in ATP.
235
Fats and carbohydrates are better than ATP for long term storage. Explain why.
The energy released in the breakdown of these molecules is used to create ATP. This occurs by reattaching a phosphate group to an ADP molecule and is an example of a condensation reaction.
236
Fill in the gaps. Due to the __________ of ATP, cells do not store _______ amounts of it. However, ATP is rapidly reformed by the ______________ of ADP. This interconversion of ATP and ADP is happening \_\_\_\_\_\_\_\_in all living cells, meaning cells do not need a large store of \_\_\_\_\_\_.
Due to the **instability** of ATP, cells do not store **large** amounts of it. However, ATP is rapidly reformed by the **phosphorylation** of ADP. This interconversion of ATP and ADP is happening **constantly** in all living cells, meaning cells do not need a large store of ATP.
237
What is the meaning of *phosphorylation*?
When a phosphate group is attached to an ADP molecule.
238
Give five properties of ATP that make it ideal to carry out its function in energy transfer.
* Small- moves easily into, out of and within cells
* Water soluble- energy-requiring processes happen in aqueous environments
* Contains bonds between phosphates with intermediate energy: most cellular needs, so that energy is not wasted as heat
* Releases energy in small quantities- quantities are suitable to most cellular needs so that energy is not wasted as heat
* Energy regenerated- can be recharged with energy
