Unit 1 - Cells and Proteins Flashcards
1
Q
Name 2 things which can be intrinsically harmful when working in a lab.
A
Chemicals
Organisms
2
Q
Who, or what, is at risk when working in a lab?
A
People working in the lab
Other organisms
The environment
3
Q
In reference to control measures, what is elimination?
A
Replace the hazardous substance with a less harmful equivalent or remove a step
4
Q
In reference to control measures, what is substitution?
A
Some hazards may be very particular to the chemical/organism involved and it may be possible to use alternatives
5
Q
In reference to control measures, what is isolation?
A
Carry out the procedure in a contained environment
6
Q
In reference to control measures, what is education?
A
Train people to follow standard methods of practise which reduce risk
7
Q
In reference to control measures, what is personal protective equipment?
A
Safety equipment
8
Q
Which control method is most preferred and which is least preferred?
A
Most preferred- elimination
Least preferred- personal protective equipment
9
Q
What is the purpose of a risk assessment?
A
Risk assessments are used to keep workers, other organisms and the environment safe, through the use of control methods.
10
Q
What is the use of a burette?
A
Used for titrations. Can make accurate measurements of small volumes (1-100 cm^3)
11
Q
What is the use of a Pipette?
A
Best used to measure volumes from 30 micro-litres to 2 cm^3. Less accurate.
12
Q
What is the use of an Auto Pipette?
A
Allows small volumes of liquid to be measured very accurately.
13
Q
What is the use of a syringe?
A
Can be used to measure from 0.5 micro-litres to 50 cm^3, very accurate If used correctly
14
Q
What is dilution?
A
Decreasing the concentration of a solution while adding another substance.
15
Q
What is the formula for calculating concentration in dilution?
A
C1V1 = C2V2
16
Q
What is Log Dilution and when is it used?
A
Involves dilution by 1/10th each time, useful when culturing microbes.
17
Q
What is a standard curve?
A
A graph of known concentrations that allows you to determine unknown concentrations.
18
Q
How can pH be controlled in an experiment?
A
pH can be controlled in an experiment by adding a buffer solution.
19
Q
How can pH be tested?
A
pH can be tested with a pH metre or universal indicator and a colour chart.
20
Q
What is centrifugation?
A
Centrifugation is a process used to separate substances by their density. As the machine spins, a solid pellet forms at the bottom of the vessel.
21
Q
What is the supernatant?
A
The supernatant is the remaining liquid left during the process of centrifugation.
22
Q
Name 3 types of chromatography.
A
Paper Chromatography
Thin-layer Chromatography
Affinity Chromatography
23
Q
What can chromatography be used to separate?
A
Chromatography can be used to separate:
- Amino acids
- Proteins
24
Q
What is responsible for the separation of molecules in chromatography?
A
Solubility is responsible for the separation of molecules in paper and thin-layer chromatography. While Affinity is responsible for separation in affinity chromatography.
25
What is electrophoresis?
In electrophoresis, proteins are put in a gel with different charges at either end, the resulting movement of the proteins differ (due to their different charges).
26
What is the main factor affecting the movement of proteins in electrophoresis?
Molecular size is the main factor affecting the movement of proteins.
27
What is the isoelectric point?
The isoelectric point of a protein is the pH at which it has an overall neutral charge.
28
What happens to a protein when it reaches its isoelectric point?
At the isoelectric point, the overall neutral charge of the protein allows it to form a solid and precipitate out of solution.
29
What are antibody techniques used to detect?
Antibody techniques are used for the detection of specific proteins.
30
What is immunoassay?
Immunoassay is a biochemical test based on antigen binding principals, that is used for detecting specific proteins.
31
What is meant by antigen binding principals?
The specificity of antibodies and their ability to recognize and bind with only one antigen.
32
What is ELISA?
ELISA (enzyme-linked immunosorbent assay) is an analytical technique which uses antibodies to detect the presence of an antigen within a solution.
33
What are the three forms of ELISA?
Direct, Indirect and Sandwich.
34
How can antibodies be labelled for detection?
Reporter enzymes catalyse a colour change reaction that is used to detect and quantify the presence of a specific antigen.
35
How does Protein Blotting work?
A mixture of proteins is extracted.
The protein mix is separated using Gel Electrophoresis.
The Gel is placed underneath a membrane filter and overlaid with absorbent paper.
A current is applied and the proteins migrate onto the filter.
A label for the protein of interest is added.
The protein of interest can now be visualised.
36
What is immunohistochemical staining used for?
Immunohistochemical staining is a technique that is used to visualise the distribution of specific cellular components in live cells.
37
What is a monoclonal antibody?
A monoclonal antibody is a supply of antibodies that are identical and will bind to exactly the same feature of the antigen.
38
What are the two types of cells fused when producing monoclonal antibodies?
B Lymphocytes and Myeloma cells are fused when producing monoclonal antibodies.
39
Why are B Lymphocytes used when producing monoclonal antibodies?
B Lymphocytes are used as they allow a specific antigen to be targeted.
40
Why are Myeloma cells used when producing monoclonal antibodies?
Myeloma cells are used since B Lymphocytes do not divide in culture, they allow duplicate cells to be produced.
41
What is the name of the cell produced when B Lymphocytes and Myeloma cells are fused?
A Hybridoma.
42
What is the technique used to fuse B Lymphocytes and Myeloma cells?
The technique used for the fusion of the two cells is Polyethylene Glycol (PEG).
43
What is a Bright Field Microscope?
A microscope used to examine whole organisms, parts of organisms or thin sections of tissue.
44
What is a Fluorescence Microscope?
A microscope used to detect specific proteins that have been fluorescently labelled antibodies.
45
What is Aseptic technique?
Aseptic technique is the procedure carried out to ensure sterile conditions.
46
What is an Inoculum?
The inoculum is the original stack of cells.
47
What is an explant?
Explants are small cuttings of whole tissue.
48
What is the piece of equipment used to calculate cell counts?
A haemocytometer is used to calculate cell counts.
49
What is the purpose of staining when making cell counts?
The purpose of staining when making cell counts is so you can see the cells.
50
What is vital staining and how does it work?
Vital staining is a method of staining where only the dead cells change colour. This allows you to distinguish between dead and living cells. Both types of cells would take up the dye but the living cells would pump it back out.
51
What is the viable cell count?
The total number of living cells in the sample.
52
What is the Non-viable cell count?
The total number of dead cells in the sample
53
What is the total cell count?
The total number of cells both living and dead in the sample.
54
How would you perform a cell count using a haemocytometer?
Work out the volume under the grid.
Divide 1 by the volume to find the number of times the volume goes into 1cm^3.
Count the cells under the grid.
Multiply the number of cells by the times the volume goes into 1cm^3 to find the cells concentration.
55
What does a Simple culture medium contain?
A simple culture medium allows conditions for gas exchange, has a suitable pH and temperature and has a suitable growing surface.
56
What is the purpose of a simple culture medium?
The purpose of a simple culture/growth medium is to provide the basic requirements for cell growth.
57
What does a complex growth medium contain?
Growth factors - stimulate proliferation (division) of cells.
Serum - Source of growth factors
Food source e.g. Glucose - Provides energy for proliferation.
pH buffer - Prevents changes in pH.
Auxins - Plant growth regulator.
58
Why is serum added to media when culturing animal cells?
Serum is added to media when culturing animal cells as it is a source of growth factors meaning it stimulates proliferation of cells.
59
What is a monolayer?
A monolayer is a single-cell, thick confluent layer of cells.
60
Why is the lifetime of primary cells shorter than that of cancer cells?
Cancer cells divide infinitely as they don't have normal controls.
61
Why are auxins added to media when culturing plant cells?
Auxins regulate plant growth, this allows the plants to grow in the most energy absorbing way.
62
What is the proteome?
The proteome is the entire set of proteins expressed by the genome.
63
What is the genome?
The genome is the entire hereditary information encoded in DNA.
64
What are the two processes responsible for the proteome being much larger than the genome?
Alternative RNA splicing and post-translational modification are responsible for the proteome being much larger than the genome.
65
Why is the entire proteome not expressed in all cells?
The entire proteome is not expressed in all cells due to regulation of gene expression.
66
Name the monomer that forms the basic structure of a protein.
Amino acids are the monomers that form the basic structure of a protein.
67
What is the polymer formed by amino acids when making proteins?
The polymer formed is a polypeptide, this is the primary level of protein structure.
68
What are the bonds involved in the basic structure of a protein and how are they formed?
Peptide bonds are involved in the basic structure of a protein.
These are formed by dehydration reactions (between a carboxyl group and an amide group.
69
What are the four main classes of amino acid side chains (R groups)?
Acidic
Basic
Polar
Non-Polar
70
For Acidic R groups;
Give an example of an amino acid
Name the type of bonding
Give a common feature
Acidic R groups are negatively charged.
Example of an amino acid is Aspartic acid.
Contains hydrophilic bonding.
Have a carboxyl group which ionises to make them acidic.
71
For Basic R groups;
Give an example of an amino acid
Name the type of bonding
Give a common feature
Basic R groups are positively charged.
Example of an amino acid is Arginine.
Contains hydrophilic bonding.
Have an additional amino group which ionises to NH3+.
72
For Polar R groups;
Give an example of an amino acid
Name the type of bonding
Give a common feature
Example of an amino acid is Glutamine.
Contains hydrophilic bonding.
Different functional groups which contain -OH, -SH or =O.
73
For Non-Polar R groups;
Give an example of an amino acid
Name the type of bonding
Give a common feature
Example of an amino acid is Glycine.
Contains hydrophobic bonding.
R-group is a hydrocarbon.
74
What is the secondary structure of a protein?
The secondary structure of protein contains three regular Sub-Structures; Alpha Helix, Beta Sheets, and turns.
75
What is an Alpha Helix?
The protein is a helix shape held together by hydrogen bonds between amino acids.
76
What are Beta sheets?
Parts of the polypeptide chain run alongside each other to form a corrugated sheet.
Antiparallel sheets have horizontal hydrogen bonds.
Parallel beta sheets have diagonal hydrogen bonds.
77
What are turns?
Reverses the direction of the polypeptide.
78
What is the type of bond involved in holding the secondary structure of proteins in place?
Hydrogen bond.
79
What is the tertiary structure of a protein?
The tertiary structure is the three-dimensional shape of a protein. This further folding is due to the interactions between R-Groups.
80
Name the types of bonds that can hold the tertiary structure in place.
```
Hydrophobic interactions
Ionic Bonds
Hydrogen Bonds
Van Der Waals interactions
Disulfide bridges.
```
81
What are Non-protein parts added to a protein?
Prosthetic groups.
82
Give two examples of prosthetic groups.
Carbohydrates
| Nucleic acid.
83
Describe a proteins quaternary structure.
Quaternary structure exists in proteins that have two or more tertiary sub-units joined together. The bonding between sub-units means that changes to the conformational shape of one polypeptide chain can affect the properties of another sub-unit in the protein.
84
Name two factors that can influence the interaction of R-groups.
pH
| Temperature.
85
How can temperature affect R-group interactions?
An increase in temperature means the kinetic energy of a protein will increase, placing stress on the bonds and breaking them.
86
How can pH affect R-group interactions?
Changes in pH affect the concentrations of H+ and OH- ions in a solution. This changes the relative charges of the protein and places stress on polar interactions such as hydrogen bonding and ionic bonding.
87
What does hydrophobic mean?
To repel or fail to mix with water.
88
What does hydrophilic mean?
To dissolve or mix with water.
89
What is the Fluid mosaic model?
The Fluid mosaic model is the currently accepted model of the plasma membrane structure.
90
What are the main components of the plasma membrane structure?
Phospholipids
| Proteins
91
Why are hydrophobic interactions significant in membrane structure?
Hydrophobic interactions between lipid tails hold the double membrane together.
92
Why are hydrophilic interactions significant in membrane structure?
Hydrophilic heads of phospholipids allow the outer layers of the membrane to be surrounded by aqueous solutions.
93
What are integral proteins?
Integral (or intrinsic) Proteins penetrate the hydrophobic interior of the membrane. They contain a stretch of non-polar amino acids in the hydrophobic region, which holds them in place.
94
What are Peripheral proteins?
Peripheral (or extrinsic) Proteins are not embedded in the lipid layer but have loose associations with the surface of the membrane.
95
Give three examples of integral proteins.
Channels
Transporters
Receptors.
96
What is a ligand?
A ligand is a substance that binds to a protein.
97
Which regions of proteins are involved in ligand binding?
Free R-groups are the regions of proteins that are involved in ligand binding.
98
What are the similarities between ligand and protein binding sites?
Ligand and protein binding sites have complementary shape and chemistry.
99
Name the type of proteins that DNA is bound around.
Histones are the type of proteins that DNA is bound around.
100
How are the charges of the DNA backbone the proteins bound around it complementary?
The DNA Backbone is negatively charged and the proteins it is bound around are positively charged.
101
What is the structure formed by the DNA Backbone being bound around Proteins?
The structure formed is called a nucleosome.
102
What is the name of the linear structure that results from the tight packaging of DNA in eukaryotes?
A chromosome.
103
What are transcripting factor proteins?
Transcripting factor proteins are proteins that bind to specific sequences of double-stranded DNA and can initiate and halt transcription by recruiting DNA polymerase.
104
What happens when a ligand binds to a protein?
The binding of a ligand to a protein results in a conformational change, which alters the behaviour of the protein.
105
What is the name of the site where a ligand binds to an enzyme?
Active Site.
106
What is the function of Phosphatase?
Removal of phosphate by hydrolysis.
107
What is the function of ATPase?
Hydrolyis of ATP.
108
What is the function of Kinase?
Transfer of phosphate group to another molecule.
109
What is the function of Synthase?
The joining of two molecules together by dehydration synthesis reaction.
110
What is the function of nuclease?
Break down of nucleic acid by hydrolysis.
111
What is the function of Polymerase?
Reaction where molecules are added in sequence to a chain (e.g. DNA or RNA synthesis)
112
What is the function of Protease?
Hydrolysis of peptide bonds, breaking down proteins.
113
What is induced fit?
The active site of an enzyme has a similar shape to the substrate that it reacts with and when the substrate joins with the enzyme, the active site changes shape to fit properly.
114
What happens to the chemical environment when binding of an enzyme and substrate occurs?
The chemical environment changes to lower the activation energy of the reaction.
115
What is an enzymes affinity for its corresponding substrate?
Enzymes have a high affinity for their corresponding substrates.
116
What is an enzymes affinity for the products of a reaction between it and its substrate?
Enzymes have a low affinity for their products.
117
What happens to the conformation of an enzyme after catalysis?
After catalysis, the products are released from the active site and the enzyme reverts to its original conformation.
118
What is an allosteric enzyme?
An allosteric enzyme is an enzyme that can have its activity altered by a ligand called a modulator.
119
What is a modulator?
A modulator is a ligand which binds to a secondary binding site away from the active site (the allosteric site) leading toa conformational change to the enzyme.
120
What are positive and negative modulators?
Negative modulators switch off enzymes.
| Positive modulators switch on enzymes.
121
Name the level of protein structure which can show co-operativity.
Quaternary protein structure can show co-operativity.
122
What is co-operativity?
Co-operativity is when changes in one protein binding site, changes the affinity of all other sub-groups.
123
How does pH affect co-operativity?
Low pH reduces co-operativity.
124
How does temperature affect co-operativity?
High temperature reduces co-operativity.
125
What is phosphorylation?
Phosphorylation is the addition or removal of a phosphate group.
126
What is the effect of adding or removing a phosphate group from a protein?
Addition or removal of phosphate groups results in a conformational change, as the position of charged bonding is altered.
127
What is dephosphorylation?
The removal of a phosphate from a molecule.
128
Name two types of protein that cane be regulated using post-translational addition of phosphate.
Enzymes
| Receptors
129
Name the group of proteins that use ATP for their phosphorylation.
ATPase's are the group of proteins that use ATP for their phosphorylation.
130
What is a sarcomere?
The basic unit of a muscle.
131
What do sacromere's contain?
Fibrous proteins called actin and myosin.
132
Describe the steps of muscle contraction.
Muscle contraction occurs when the muscles receive an impulse from a nerve cell.
The impulse causes myosin binding sites on actin to be exposed.
The myosin heads form a flexed shape and bind to the actin.
ADP and Pi are released from the myosin, causing it to return to its relaxed shape; this moves the actin filament to the centre of the sarcomere.
ATP binds to the myosin head, which causes it to release the actin.
The myosin head acts as an ATPase; it breaks down the ATP to ADP+Pi, causing the head of the myosin to flex again.
133
Name two small molecules which can diffuse directly across the phospholipid bi-layer.
Oxygen
| Carbon Dioxide.
134
Why does the bi-layer act as a barrier to most other ions and molecules.
Because molecules that are too large or too polar cannot diffuse directly across the phospholipid bi-layer, so require to be transported.
135
What do channel proteins do?
Allow passive transport down concentration gradients.
136
What do transporter proteins do?
Actively moves molecules across the membrane against concentration gradients.
137
What do receptor proteins do?
Receives signals and brings about responses.
138
What is the membrane protein involved in the passive transport of water?
Aquaporin 2.
139
What are the two types of gated channels?
Ligand-gated channels
| Voltage-gated channels.
140
How do Ligand-gated channels operate?
Ligand-gated channels open (or close) following the binding of a ligand.
141
How do Voltage-gated channels operate?
Voltage-gated channels respond to changes in ion concentration.
142
What is facilitated transport?
Facilitated transport is a passive process, meaning that it does not require energy. It involves a conformational change in the protein.
143
What does intracellular mean?
Intracellular means inside the cell.
144
What does extracellular mean?
Extracellular means outside the cell.
145
What is the name of the membrane protein that binds to signal molecules?
Receptor protein.
146
What is the type of pathway activated when a signal molecule is received?
Signal transduction pathway.
147
State four potential responses of a cell to a signal molecule.
Activation of special enzymes or G-Proteins.
Changes in molecule uptake or release.
Rearrangement of the cytoskeleton.
Activation of proteins that regulate gene expression.
148
What is the Sodium-Potassium pump also known as?
Na/KATPase
149
How does the Sodium-Potassium pump work?
Ions are pumped against a steep concentration gradient.
The action of the sodium-potassium pump has significant energy requirements.
The pump will have a high affinity for the Na+ inside the cell, three Na+ ions bind to the pump, this allows ATP to bind to the pump, changing its shape, then releasing the Na+ outside the cell. This allows K+ to bind which changes the shape so the K+ is released inside the cell. The process then repeats.
150
What are the functions of NA/KATPase?
Maintenance of osmotic balance in cells.
Generation of ion gradient for glucose symport.
Generation and long term maintenance of ion gradient for resting potential in neurons.
Generation of ion gradient in Kidney tube.
151
Why is the Sodium-Potassium pump important in mammalian metabolism?
The generation of ion gradient by NA/KATPase accounts to a significant part of the basal metabolic rate in mammals. (25% in humans).
152
what does de-polarisation mean?
Neurons become more positive as less negative.
153
What is nerve transmission?
Caused by a wave of depolarisation, and is how electrical impulses are passed from one neuron to the next.
154
What does resting potential mean?
Difference in voltage across the membrane when there is no signal being sent or received.
155
Describe the process of nerve transmission.
Resting potential of membrane is stable - slightly negative inside neuron.
Neurotransmitter binds to Ligand-gated channel.
Ligand-gated channels open and Na+ enters neuron.
Neuron becomes less negative.
If threshold is reached, voltage changes and voltage-gated ion channels open, Na+ floods into neuron.
Increased Na+ causes a wave of depolarisation through the neuron.
156
Name the three domains photoreceptor systems are found across.
Archaea
Bacteria
Eukaryotes
157
What is the function of Bacteriarhodopsin in the photoreceptor system?
Bacteriarhodopsin generates potential differences by absorbing light to pump protons across membranes.
158
What is the name of the pigment that absorbs light energy in light cells?
Chlorophyll.
159
How does light absorption effect the movement of hydrogen ions in the chloroplast.
When a chlorophyll absorbs light, an electron is passed/boosted to a higher energy level. This passes along a series of protein carriers.
160
How do hydrogen ions drive ATP synthase?
Hydrogen ins are pumped across the membrane. The hydrogen ions pumped across diffuse through ATP synthase, resulting in the production of ATP.
161
What is the plant membrane called?
A thylakoid membrane.
162
What is the membrane protein that is important in the animal photoreceptor system?
Opsin membrane protein.
163
How does the opsin membrane protein form the photoreceptor proteins of the eye.
When opsin binds with retinal, rhodopsin is formed. Different forms of opsin that combine with retinal give sensitivity to specific wavelengths of light; red, green, blue, UV.
164
What are the two types of cells found in animal eye structures that are involved in light absorption?
Rod cells
| Cone cells.
165
What are cone cells?
Cone cells are not as sensitive to light as rod cells, but have the ability to distinguish colour.
166
What are rod cells?
Rod cells enable us to see at night but only in black and white as they do not allow us to distinguish colour.
167
What must happen to give rod cells sensitivity at low light intensities?
In rod cells, the rhodopsin absorbs a wide range of wavelengths, and a greater degree of amplification from a single photon of light results in sensitivity at low light intensities.
168
What happens when rhodopsin is stimulated by a photon of light?
A nerve impulse can be generated.
169
Describe the process of a nerve impulse being generated by a photon of light stimulating rhodopsin.
One photon of light stimulates rhodopsin.
Active rhodopsin activates hundreds of G-Protein molecules and transducin.
Transducin activates enzyme phosphodiesterase.
Phosophodiesterase stimulates conversion of cyclic GMP into GMP which closes Na+channels.
Less Na+ means rod cell is hyperpolarised.
Nerve impulse is generated.
170
Name 3 things that allow co-ordination to be achieved in multi-cellular organisms.
Signalling molecules.
Receptors
Responses.
171
What happens when a signal molecule binds to a receptor?
A conformational change.
172
What is the Sodium-Potassium pump also known as?
Na/K-ATPase.
173
What are the energy requirements for Na/K-ATPase?
Na/K-ATPase has significant energy requirements.
174
How does the Sodium-Potassium pump work?
Ions are pumped against a steep concentration gradient.
The pump has a high affinity for the Na+ inside the cell. Three Na+ ions bind to the pump, this allows ATP to also bind to the pump causing a conformational change which changes its shape and release the Na+ outside the cell. This allows two K+ to bind which changes the shape again, releasing K+ inside the cell. This process then repeats.
175
What are the functions of Na/K-ATPase?
Maintenance of osmotic balance in cells.
Generation of the ion gradient for glucose symport.
Generation and long-term maintenance of ion gradient for resting potential in neurons.
Generation of ion gradient in Kidney Tube.
176
Why is the Sodium-Potassium pump so important in mammalian metabolism?
The generation of ion gradient by Na/K-ATPase accounts to a significant part of the basal metabolic rate. (25% in humans)
177
What is De-polarisation?
Neurons become more positive and less negative.
178
What is nerve transmission?
How electrical impulses are passed from one neuron to the next. Caused by a wave of de-polarisation.
179
What is resting potential?
The difference in voltage across the membrane when there is no signal being sent or received.
180
Describe the process of transmission of nerve impulses.
Resting potential of membrane stable - Slight negative inside the neuron.
Neurotransmitter (ligand) bins to Ligand-gated channel.
Ligand-gated channels open and Na+ enters the neuron, which becomes less negative.
If the threshold is reached, voltage changes and Voltage-gated ion channels open.
Na+ floods into the neuron.
Increased Na+ causes a wave of de-polarisation.
181
What are the three domains in which photoreceptors are found?
Archaea
Bacteria
Eukaryotes
182
What is the role of Bacteriorhodopsin in the photoreceptor system?
Bacteriorhodopsin generates potential differences by absorbing light to pump proteins across membranes.
183
What is the name of the pigment that absorbs light energy in plant cells?
Chlorophyll.
184
How does light absorption affect the movement of hydrogen ions in the chloroplast?
When chlorophyll absorbs light, an electron is passed/boosted to a higher energy level. This passes along a series of protein carriers.
185
How do hydrogen ions drive ATP synthase?
The hydrogen ions pumped across the membrane diffuse through ATP synthase, resulting in the production of ATP.
186
What is the plant membrane called?
A thylakoid membrane.
187
What is the name of the membrane protein that is important in the animal photoreceptor system?
Opsin membrane protein.
188
How does the opsin membrane protein form the photoreceptor proteins of the eye?
When opsin binds with retinal, rhodopsin is formed. Different forms of opsin that combine with retinal give sensitivity to specific wavelengths of light; red, green, blue, UV.
189
What are the two cell types found in animal eye structures that are involved in light absorption?
Rod cells
| Cone cells.
190
What are cone cells?
Cone cells are not as senstive to light as rod cells, but have the ability to distinguish colour.
191
What are rod cells?
Rod cells enable us to see at night but only in black and white as they do not allow us to distinguish colour.
192
How do rod cells gain sensitivity at low light intensities?
A greater degree of amplification from a single photon of light results in sensitivity at low light intensities.
193
Describe the process of a nerve impulse being generated in photoreceptors.
One photon of light stimulates rhodopsin.
Active rhodopsin activates hundreds of G-Protein molecules and transducin.
Transducin activates enzyme phosphodiesterase.
Phosphodiesterase stimulates conversion of cyclic GMP into GMP which closes Na+ channels.
Less Na+ means rod cell is hyperpolarised.
Nerve impulse is generated.
194
Name 3 things that allow co-ordination to be achieved in multi cellular organisms.
Signalling molecules
Receptors
Responses
195
What happens when a signal molecule binds to a receptor?
A conformational change
196
Where are receptors for hydrophobic signals found?
In the nucleus of cells
197
How do hydrophobic signals cross the membrane?
Hydrophobic signals diffuse through the membrane due to hydrophobic nature.
198
Give two examples of hydrophobic signalling molecules.
Throxyine
| Testosterone
199
What is a transcription factor?
Transcription factors directly influence the transcription in genes.
200
How are thyroid hormones used to control the transcription of the Sodium-Potassium pump?
Thyroid receptor binds to DNA in absence of thyroxine, preventing transcription of the gene for Na/K-ATPase.
Thyroxine binds to receptor causing a conformational change, leading to de-binding of DNA, allowing transcription of Na/K-ATPase.
201
Where are the receptors for hydrophilic signals found?
On the cell surface.
202
Give two examples of hydrophilic signalling molecules/
Peptide Hormones
| Neurotransmitters
203
What are the three stages of communication?
Reception - Signal molecule binds to a receptor protein.
Transduction - Conformation change of protein followed by the activation of other molecules and the amplification of a signal.
Response - Activation of other cellular action e.g. Transcription or movement of the cytoskeleton
204
Do hydrophilic signals enter the cell?
Only the signals are transduced across the membrane, the molecule is not.
205
State two possible outcomes of hydrophilic signals.
Cascades of G-Proteins
| Phosphorylation by Kinases
206
How are signals transduced using G-protein linked receptors?
Signal molecule binds to the receptor protein, causing a conformational change. This causes GDP to be displaced by GTP which activates the G-protein. This G-protein then activates an enzyme, causing a cellular response.
207
How are signals transduced using Phosphorylation?
When a signal molecule binds to a receptor tyrosine kinase (RTK), this causes a conformational change. This is due to the tyrosine amino acids becoming phosphorylated. This then activates the kinase domains in the RTK, causing various cellular responses.
208
What is insulin?
Insulin is a peptide hormone. Its receptor is found outside the cell membrane. When these two bind, a cascade of phosphorylation occurs, recruiting GLUT4 (glucose transporter). GLUT4 can be found in fat and muscle cells. This molecule allows the passage of glucose.
209
What is Diabetes Mellitus?
A condition in which insulin is not produced. Know as type 1 diabetes.
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What is type 2 diabetes?
The loss of receptor function.
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What is the structure responsible for maintaining the shape and structure of all organelles, and what is it composed of?
Cytoskeleton and is composed of microtubules.
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What happens to the cytoskeleton during cell division?
The cytoskeleton is re-organised.
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What are microtubules made up of?
Microtubules are made up of a globular protein called tubulin.
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Where are microtubules found?
Microtubules are found within eukaryotic cells, radiating from the centrosome.
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What do microtubules do during cell division?
Microtubules form spindle fibres during cell division.
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What is the function of the cell cycle?
To regulate the growth and replacement of genetically identical cells.
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What is the name of the condition that could result from the uncontrolled decrease in the rate of the cell cycle?
Degenerate diseases such as Parkinson's.
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How may a tumour form?
Uncontrolled increase in the rate of the cell cycle.
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What are the three stages of interphase?
G1- first gap phase where proteins and organelles are synthesised.
S- Synthesis phase for continued growth and DNA replication.
G2- 2nd gap phase where proteins and organelles are synthesised.
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What are the stages of mitosis?
```
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
```
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What is prophase?
Chromatin condenses into sister chromatids and mitotic spindles form between centrosomes.
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What is metaphase?
Nuclear membrane breaks up and centrosomes are now at opposite poles. Chromosomes line up at the metaphase plate. Microtubules attach to the kinetochore.
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What is anaphase?
Microtubules shorten, pulling sister chromatids apart to opposite poles.
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What is telophase?
Cell lengthens and nuclear membrane reforms around chromosomes at each pole. Chromosomes begin to uncoil.
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What is cytokinesis?
Cytoplasm divides, creating 2 new identical cells.
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What are the 3 checkpoints that occur during the cell cycle?
G1 checkpoint - Checks cell size as sufficient growth must have occurred to enter the 'S' phase.
G2 checkpoint - DNA replication must be complete for the cell cycle to continue past this checkpoint.
Metaphase checkpoint - Controls entry to anaphase, ensures that chromosomes are correctly aligned on the metaphase plate.
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What is the most significant checkpoint?
G1 checkpoint.
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What happens if a cell does not pass the G1 checkpoint?
Cell enters G0 (non-proliferating stage).
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What happens to cell size at G1?
Cell size increases and cyclic cells also accumulate.
230
What is the role of Cdks in the control of the cell cycle?
The activation of Cdk's (Cyclic dependant kinases) causes phosphorylation of proteins that stimulates the cell cycle.
231
What happens if a cell does not reach the threshold of a checkpoint?
The cell is held at that checkpoint.
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What protein is activated when DNA is damaged?
p53
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Name 3 things that may happen if DNA is damaged during 'S' phase.
Stimulation of DNA repair
Arrests the cell cycle
Causes the cell to die.
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What is apoptosis?
The programmed death of a cell.
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What are the two enzymes involved in Apoptosis?
Caspases (proteinases but Not DNAases)
| DNAases
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How may Apoptosis be triggered from out with the cell?
By a lymphocyte.
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How does p53 activate Apoptosis?
Once activated p53 activates a caspase cascade which causes cell death when there are no growth factors present.
