Unit 1 Flashcards
1
Q
What is a hazard?
A
A hazard is anything that poses a potential threat to an individual or the environment.
2
Q
What is a risk?
A
A risk is the likelihood of harm arising from exposure to a hazard.
3
Q
What are examples of hazards in the lab?
A
Toxic and corrosive chemicals, heat or flammable substances, pathogen organisms and mechanical equipment.
4
Q
When should a risk assessment be carried out?
A
Before any practical work in the lab.
5
Q
What do risk assessments involve?
A
Identifying hazards, risks and control measures to minimise risk.
6
Q
What do control measures include?
A
Using protective handling techniques, protective clothing and equipment and Aseptic Technique.
7
Q
Why is Personal Protective Clothing worn?
A
PPE is worn to reduce the risk of harmful substances coming into contact with the body.
8
Q
What should be considered when choosing apparatus for working with liquids and solutions?
A
Accuracy: How close the measurement is to the true value and Precision: How close the values are to each other.
9
Q
When and how are linear dilutions carried out?
A
For small dilutions, this is achieved by using different volumes of the same stock solution combined with different volumes of a suitable solvent- Dilutions will differ by an equal interval.
10
Q
When and how are log dilutions carried out?
A
For large dilutions, this is achieved by using successive dilutions as the new stock- Dilutions will differ by a constant proportion.
11
Q
What is a standard curve used to determine?
A
A series of standards of known concentrations are measured and graphed. This graph can be used to determine the concentration of an unknown solution.
12
Q
What are titrations used to determine and how are they carried out?
A
Titrations can be used to determine the concentration of an unknown solution. These are carried out using a burette to deliver a solution of known concentration to a solution of unknown concentration below.
13
Q
How can titration be used to calculate the concentration of a solution?
A
The volume and concentration of the known solution needed to reach the endpoint of the reaction with a known volume of the other solution can be used to calculate the unknown concentration using V1xC1=V2xC2.
14
Q
How are buffers used to control an experiment?
A
It allows the pH of the reaction to be kept constant because the addition of acid or alkali has little effect on the pH of the buffer.
15
Q
What does a colorimeter measure?
A
A colorimeter measures the absorbance or transmission of light through a solution.
16
Q
How does a colorimeter work?
A
A colorimeter works by passing a light beam at a specific wavelength through a cuvette containing a sample. Some light is absorbed by the sample, light transmitted is detected as an absorbance value.
17
Q
Why does a colorimeter need to be calibrated and how is this done?
A
The correct wavelengths of light must be selected when using a colorimeter. An appropriate reference blank (e.g distilled water) is placed in the colorimeter and the calibration button is pressed. This is used to provide a baseline reading (0). This shows the absorbance when the sample is absent.
18
Q
How is concentration measured using a colorimeter?
A
By measuring the absorbance of light by a sample we can determine the concentration of a coloured substance using suitable wavelength filters as there is a linear relationship between absorbance and concentration.
19
Q
How is turbidity measured using a colorimeter?
A
By measuring the percentage transmission of light through a sample, we can measure turbidity. The lower the transmission the higher the turbidity.
20
Q
What component parts can biological systems be separated by?
A
Solubility, size, shape or charge.
21
Q
How does a centrifuge work?
A
A centrifuge spins a sample at high speed to separate the mixture based on density. The densest materials form a pellet at the bottom of the tube. Less dense components remain in the mixture.
22
Q
What is paper and thin layer chromatography used for?
A
For separating different substances such as amino acids and sugars based on solubility in specific solvents.
23
Q
How does affinity chromatography work and what does it separate?
A
Affinity chromatography is a separation technique that separates proteins based on their solubility. The mixture is passed through a column containing ligands complementary to target proteins. Target proteins bind, are removed from the mixture, and washed out in a final wash.
24
Q
What is gel electrophoresis used to separate and how does it work?
A
Proteins and nucleic acids. Charged macromolecules move through an electric field applied to the gel matrix.
25
What does gel electrophoresis separate by?
Separates proteins based on charge and/or shape/size.
26
How does native gel electrophoresis work?
Proteins are not denatured before electrophoresis allowing analysis in their folded state and separation can be done based on size, shape and charge.
27
How does SDS-Page electrophoresis work?
Proteins are denatured prior to the procedure and they are given a uniform negative charge. This separated proteins on size alone.
28
What is a protein's isoelectric point?
The IEP is the pH at which a soluble protein has no net charge and will precipitate out of the solution. Proteins can be separated based on their IEP.
29
How can proteins be separated using their isoelectric point?
If the solution is buffered to a specific pH, only the proteins that have an IEP of that will precipitate. Proteins can also be separated using their IEP in electrophoresis.
30
What are immunoassay techniques used for and how is this achieved?
To detect and identify specific proteins using stocks of antibodies with the same specificity, that recognise one antigen, known as monoclonal antibodies.
31
How do scientists know when a monoclonal antibody has bound to the target protein?
Antibodies are linked to a chemical label which signals when binding has occurred. The label is often a reporter enzyme producing a colour change or another signal.
32
How does western blotting work?
The separated proteins are transferred from the gel onto a solid medium after SDS-Page electrophoresis. The proteins are identified using specific antibodies with reporter enzymes.
33
What is bright field microscopy commonly used to observe?
Whole organisms, parts of organisms, thin sections of dissected tissue or individual cells.
34
How does fluorescence microscopy work?
Fluorescence microscopy uses specific fluorescent labels to bind to and visualise certain molecules or structures within cells or tissues.
35
How do aseptic techniques work and what do they achieve?
Aseptic techniques eliminate unwanted microbial contaminants when culturing microorganisms or cells. This involves the sterilisation of equipment and culture media by heat or chemical means.
36
How can a microbial culture be started?
Microbial cultures can be started using an inoculum of microbial cells on an agar medium, or in a broth with suitable nutrients.
37
What does a medium for growing animal cells contain?
Mediums for growing animal cells contain growth factors from serum. These are proteins that promote cell growth and proliferation and are essential.
38
What are the lifetimes of primary and tumour cell lines?
In culture, primary cell lines can divide a limited number of times, where as tumour cell lines can perform unlimited division.
39
What does plating out a liquid micro-bacterial culture on solid media allow?
The number of colony-forming units to be counted and the density of cells to be estimated. Serial dilutions are often needed to achieve a suitable colony count.
40
What does a haemocytometer allow for?
an estimation of the number of cells in a liquid culture to be calculated.
41
How are haemocytometers used?
Estimates of viable and total cell counts can be made using haemocytometers by counting the cells in an area of the grid and calculating using the volume of the area of the grid. Trypan blue die is absorbed by dead cells so total and viable counts can be achieved.
42
How does vital staining work?
Vital staining is required to identify and count viable cells by adding a stain to a cell culture and observing which cells have taken up the stain.
43
What is the proteome?
The entire set of proteins expressed by a genome.
44
Why is the proteome larger than the genome?
Due to alternative RNA splicing and post-translational modification as more than one protein can be expressed from a single gene.
45
What do genes that don't code for proteins?
Not all genes are expressed as proteins in a particular cell type, genes that do not code for proteins are called non-coding RNA genes and RNA molecules that control the expression of other genes.
46
What conditions can cause the set of proteins expressed by a cell to vary?
Metabolic activity of the cell, cellular stress, response to signalling molecules and diseased vs healthy cells.
47
What system do eukaryotic cells have in place to increase the total area of membrane available?
As eukaryotic cells have a small surface area to volume ratio the area is too small to carry out vital functions. They have a system of internal membranes available for cellular functions.
48
What does the endoplasmic reticulum form a network of?
The ER forms a network of membrane tubules continuous with the nuclear membrane.
49
What is the endoplasmic reticulum involved in?
The synthesis of lipids and proteins.
50
When is the ER referred to as the rough ER
When ribosomes are on its cytosolic face.
51
What is the Golgi apparatus?
A series of flattened membrane discs.
52
What is the Golgi apparatus involved in?
The transport and modification of proteins.
53
What are lysosomes?
Membrane-bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acids and compartments.
54
What is the function of vesicles?
Vesicles transport materials between membrane compartments.
55
What ER are lipids synthesised in and where do they go afterwards?
Lipids are synthesised in the smooth ER and are inserted into the membrane.
56
Where does the synthesis of proteins begin?
The synthesis of all proteins begins in the cytosolic ribosomes.
57
Where are the cytosolic proteins transferred to after synthesis in the ribosome?
To the cytosol.
58
How do transmembrane proteins halt translation and where do they go?
A signal sequence halts translation and directs the ribosome to dock with the ER, forming RER. The protein is inserted into the ER membrane.
59
What is a signal sequence?
A short stretch of amino acids at one end of the polypeptide that determines the eventual locations of a protein in a cell.
60
Where do proteins go after they enter the ER?
The proteins are transported by vesicles and fuse with the Golgi apparatus.
61
What happens to proteins in the Golgi apparatus?
As proteins move through the Golgi apparatus they undergo post-translation modification.
62
What is the main modification occurring to proteins in the Golgi?
The addition of carbohydrate groups is the major modification taking place.
63
Where do vesicles that leave the Golgi take proteins to?
Vesicles that leave the Golgi apparatus take proteins to the plasma membrane and lysosomes.
64
Where are secret proteins translated?
Secreted proteins are translated in the ribosome on the RER and enter its lumen.
65
Where do secreted proteins go after they move through the Golgi apparatus?
Secreted proteins are packaged into secretory vesicles. These vesicles move to and fuse with the plasma membrane, releasing the proteins out of the cell.
66
What is protealytic cleavage?
The process of breaking peptide bonds between animism acids in proteins.
67
How are many secreted proteins synthesised?
Many secreted proteins are synthesised as inactive precursors and require proteolytic cleavage to produce active proteins. (stops digestive enzymes damaging cells).
68
What are proteins made from?
Proteins are polymers of amino acids.
69
What bonds are amino acids linked by?
Amino acids are linked by peptide bonds to form polypeptides.
70
What differs in the structure if amino acids?
Amino acids have the same basic structure only differing in the R group present.
71
What do amino acid R groups vary in?
Shape, size, charge, hydrogen bonding capacity and chemical reactivity.
72
What are the 4 classifications of R groups?
Acidic- negatively charged
Basic- positively charged
Polar
Hydrophobic- non polar
73
What determines the function of a protein?
The wide variety of functions carried out by proteins results from diversity of R groups.
74
What is the primary structure of a protein?
The primary structure is simply the sequence in which the amino acids are synthesiser into a polypeptide.
75
What is the secondary structure in a protein?
Hydrogen bonding along the backbone of the protein strands results in regions of secondary structure.
76
What are the 3 types of secondary structure?
A-helix, parallel or anti-parallel beta-sheet and turns.
77
What is the tertiary structure of a protein?
Tertiary structure involved the folding of the polypeptide chains to give a more complex 3D structure.
78
What interactions between R groups stabilises the conformation if a tertiary structure?
Hydrophobic interactions, ionic bonds, LDFs, hydrogen bonds and disulphide bridges.
79
What are disulphide bridges?
Disulphide bridges are covalent bonds formed between R-groups containing sulphur.
80
What is quaternary structure of a protein?
Quaternary structure exists in proteins with two or more connected polypeptide subunits. (This describes the a partial arrangement of subunits).
81
What is a prosthetic group?
Prosthetic groups are non protein unit tightly bound to a protein and necessary for its function. (eg haem for binding of oxygen to haemoglobin)
82
How does increasing temperature effect interactions if the R groups?
Increasing temperature disrupts interactions that hold the protein in shape. The protein unfolds and becomes denatured.
83
How does pH effect the charges of the R groups?
The charges on acidic and basic R groups are affected by pH. As H increases or decreases from from the optimum, the normal ionic interaction between charged groups are lost. This changes the shape of the protein.
84
What is a ligand?
A ligand is a substrate that can bind to a protein.
85
What R-groups allow binding to ligands?
R-groups not involved in protein folding can allow binding to ligands.
86
What do binding sites have that is complimentary to the ligand?
Binding sites will have complementary shape and chemistry to the ligand.
87
What does a ligand do to a molecule?
Changes the conformation of the protein and causing a functional change in the protein.
88
Where do allosteric interactions occur between?
Allosteric interactions occur between specially distant sites.
89
What structure are allosteric proteins normally?
Many allosteric proteins consist of multiple subunits (quaternary structure).
90
What do allosteric proteins with multiple subunits show?
Allosteric proteins with multiple subunits show co-operativity in binding.
91
How does co-operativity in binding work?
The binding of a substrate to one active site of an allosteric enzyme increases the affinity of the other active sites for binding of subsequent substrate molecules.
92
What does affinity mean?
The attractive force binding atoms in molecules
93
What do allosteric enzymes contain on top of the active site?
Allosteric enzymes contain a second type of site called an allosteric site.
94
What do modulators regulate in an enzyme?
Modulators regulate the activity of the enzyme when they bind to the allosteric site.
95
How do modulators effect the active site of an enzyme?
Following the binding of a modulator, the conformation of the enzyme changes and thus alters the affinity of the active site for the substrate.
96
What is the difference between positive and negative modulators?
Positive modulators increase the enzymes affinity and negative modulators decrease the enzymes affinity.
97
What shows co-operativity in haemoglobin?
The binding and release of oxygen in haemoglobin shows co-operativity. Haemoglobin has a relatively low number oxygen affinity but one molecule binding increases the affinity of the other 3 haem groups.
98
What does a rightward shift in the dissociation curve for oxygen indicate?
Decreased affinity of haemoglobin for oxygen, making it harder to bind to oxygen in the lungs and easier to release oxygen to respiring tissues.
99
What does a leftward shift in the dissociation curve for oxygen indicate?
Increased affinity of haemoglobin for oxygen, making it easier to bind the oxygen in the lungs but harder to release oxygen to respiring tissues.
100
What happens to affinity of haemoglobin for oxygen as temperature increases?
As temperature increases, affinity of haemoglobin for oxygen decreases so oxygen binding is reduced.
101
What happens to the affinity of haemoglobin for oxygen as pH decreases?
As pH decreases, affinity of haemoglobin for oxygen decreases so binding of oxygen is reduced.
102
How can an increase in oxygen delivery to tissue be promoted?
A decrease in pH and an increase in temperature in actively respiring tissue.
103
What can the addition or removal of phosphate from R-groups be used to cause?
The addition or removal of phosphate from particular R-groups can be used to cause reversible conformational changes in proteins.
104
What catalyses the transfer of a phosphate group?
Protein kinases catalyse the transfer of a phosphate group to other proteins.
105
Where is ATP transferred to by kinase?
The terminal phosphate of ATP is transferred to specific R-groups.
106
What catalyses the de-phosphorylation of proteins?
Protein phosphatases catalyse the de-phosphorylation of proteins.
107
How does phosphate change the conformation of a protein?
The addition of phosphate adds a negative charge to the protein. This can disrupt the ionic interactions in the protein and create new ones.
108
How does phosphorylation affect a proteins activity?
Phosphorylation brings about conformation changes, which can affect a protein’s activity.
109
What does phosphorylation regulate?
The activity of many cellular proteins, such as enzymes and receptors. Some proteins are activated by phosphorylation and some are inhibited.
110
What is it meant by the fluid mosaic model in the membrane?
Cell membranes are composed of proteins imbedded with a phospholipid bilayer. This structure is described as a fluid mosaic model.
111
What are phospholipids composed of?
A hydrophilic head and a hydrophobic tail.
112
What is the difference between integral and peripheral membrane proteins?
Peripheral proteins lie on the surface of the membrane attached to phospholipid heads and integral proteins lie within the membrane.
113
What holds integral proteins in the membrane?
Regions of hydrophobic R-groups allow strong hydrophobic reactions with the hydrophobic region of membrane phospholipids. This holds integral membrane proteins within the phospholipid bilayer.
114
What are integral proteins that go all the way through the membrane called?
Transmembrane proteins.
115
How are peripheral proteins held to the membrane?
Peripheral membrane proteins have hydrophilic R-groups in their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bonding.
116
What surface do peripheral proteins often interact with aside from the membrane?
Many peripheral membrane proteins interact with the surface of integral proteins.
117
What does ten phospholipid bilayer act as a barrier to?
The phospholipid bilayer is semi-permeable. It acts as a barrier to ions and most uncharged pole molecules.
118
What molecules can pass through the bilayer via simple diffusion?
Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by diffusion?
119
What 2 types of molecule can pass through the membrane freely?
Hydrophobic molecules (oxygen) and small uncharged polar molecules (water).
120
What 2 types of molecule cannot pass through the membrane freely? i’m
Large uncharged polar molecules (glucose) and ions (chloride).
121
What is facilitated diffusion?
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins. These are either channels or transporter proteins.
122
What membrane proteins do different cell types have to preform different specialised functions?
To preform specialised functions different cell types have different channel and transporter proteins.
123
How selective are most channel proteins in animal and plant cells?
Most channel proteins in animal and plant cells are highly selective.
124
How to channel proteins created water filled pores that extend across the membrane?
Channels are multi-subunit proteins with the subunits arranged to form water filled pores that extend across the membrane.
125
How do gated channel proteins allow or prevent diffusion?
Gated channel proteins change conformation to either allow or prevent diffusion.
126
What are the two types of channel proteins?
Ligand gated and voltage gated.
127
How are ligand gated channel proteins controlled?
Ligand gated channel proteins are controlled by the binding of signal molecules and allow the passage of solutes by alternating the conformation.
128
How are voltage gated channel proteins controlled?
Voltage gated channel proteins are controlled by ion concentration.
129
How do transporter proteins work?
Transporter proteins bind to the specific substrate to be transported and undergo a conformation change to transfer the solute across the membrane. These proteins alternate between 2 conformations.
130
What proteins does active transport use to transfer substances across the membrane?
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
131
What is required for active transport?
A source of metabolic energy is required for active transport.
132
What do some active transport proteins do to provide energy for the conformation change easily?
Some active transport proteins hydrolyse ATP directly to provide energy for the conformational change required to move substances across the membrane. These are called ATPases.
133
How is a membrane potential created?
A membrane potential is an electrical potential difference across the membrane and is created when there is a difference in electrical charge on the two sides of the membrane.
134
How is a electrochemical gradient determined for a charger molecule?
For a solute carrying a net charge, the concentration gradient and the electrical potential difference combine to create the electrochemical gradient that determines the transport of the solute.
135
How do ion pumps establish and maintain ion gradients?
Ion pumps, such as the sodium potassium pump use energy from the hydrolysis of ATP to establish and maintain ion gradients.
136
What is the role of the sodium potassium pump?
The sodium potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis.
137
What does the sodium potassium pump transport in and out of the cell?
The sodium potassium pump transports 3 sodium ions out the cell and 2 potassium ions into the cell.
138
How does the sodium potassium pump work?
1. The pump has a high affinity for sodium ions inside the cell so 3 sodium ions bind.
2. Binding stimulates phosphorylation by ATP which causes a conformational change.
3. The affinity for sodium ions decreases and sodium ions are released outside of the cell.
4. The conformational change causes the protein to have high affinity for potassium ions and 2 potassium ions bind. This triggers de-phosphorylation.
5. Lows of the phosphate group causes a conformational change.
6.Potassium ions are released inside the cell and affinity returns to start.
139
In what cells is the sodium potassium pump often found?
The sodium potassium pump is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms.
140
How is glucose transported in the small intestine?
The sodium gradient created by the sodium potassium pump drives the active transport of glucose. This allows glucose to be absorbed from the small intestine into the bloodstream.
141
How to multicellular organisms signal between cells?
Multicellular organisms signal between cells using extra cellular signalling molecules. These include hormones and neurotransmitters.
142
What are receptor molecules?
Receptor molecules of target cells are proteins with a binding site for a specific signalling molecule.
143
How does binding change the receptor molecule?
Binding changes the conformation of the receptor which initiates a response with within a cell.
144
How do cells insure that a signal reaches the right receptor?
Different cell types produce specific signals that can only be detected and respond to by cell with the specific receptor.
145
What may happen if a there are response molecules in different cell types.
In multicellular organisms, different cell types may show a tissue-specific response to the same signal.
146
What type of signalling molecules can diffuse through the membrane?
Hydrophobic signalling molecules are able to directly diffuse through the phospholipid bilayer of membranes and can bind to intercellular receptors.
147
How to steroid hormones transmit signals?
Steroid hormones are lipophilic (fat loving) and can diffuse freely across the plasma membrane. E.g - osteogenesis and testosterone. They bind to specific receptors in the cutis op or nucleus. And travel to the nucleus to bind to DNA at specific sites called hormone response elements
148
How to peptide hormones transmit signals?
Peptide hormones are hydrophilic and lipophobic (fat hating). They cannot freely diffuse across the plasma membrane if a cell and bind to receptors on the surface. E.g- insulin and glucagon.
149
What are neurotransmitters?
Neurotransmitters are chemical messengers. They transmit their messages across a synapse.
150
What are transcription factors?
Transcription factors are proteins that when bound to DNA can either stimulate or inhibit transcription. The receptors for hydrophobic signalling molecules are transcription factors.
151
Where does a hormone-receptor complex go after the hormone has bound?
Hormone receptor complexes move to the nucleus where they bind to specific sites on DNA and affect gene expression.
152
Where do hydrophilic signalling molecules bind to?
Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol.
153
What happens to receptors after a hydrophilic signalling molecule binds?
Transmembrane receptors change conformation when the ligand binds to the extra cellular face. The signal molecule does not enter the cell but the signals are transduced across the membrane.
154
What do transmembrane receptors convert?
Transmembrane receptors act as signal transducers by converting the extra cellular ligand binding into specific intracellular signals which alter the behaviour of the cell.
155
What do transduced hydrophilic signals often involve?
Transduced hydrophilic signals often include G-proteins and cascades of phosphorylation by kinase enzymes.
156
What is a benefit of phosphorylation cascades?
Phosphorylation cascades allow more that one intracellular pathway to be activated.
157
What does binding of the peptide hormone insulin to its receptor result in?
Binding of the peptide hormone insulin to its receptor results in an intracellular signal cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell of fat or muscle cells.
158
What can diabetes be caused by?
Diabetes can be caused by failure to produce insulin (type one) or loss of receptor function (type two). Type two is usually associated with obesity.
159
How can type two diabetes be cured?
Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2.
160
What is resting membrane potential?
Resting membrane potential is a state where there is no net flow of ions across the membrane.
161
What triggers the start of depolarisation and transmission of a nerve impulse?
The transmission of a nerve impulse requires changes in the membrane potential of the neurons and plasma membrane.
162
What is an action potential?
An action potential is a wave of electrical excitation along a neurons plasma membrane.
163
How to neurotransmitters initiate a response in neurons
Neurotransmitters initiate a response by binding to their receptors at a synapse.
164
How does depolarisation of the plasma membrane begin?
Depolarisation if the plasma membrane begins as a result of the entry of positive ions.
165
What does the entry of positive ions into a neuron trigger
Triggers the opening of voltage gated sodium channels, further depolarisation occurs.
166
How is a membrane potential restored?
Inactivation if the sodium channels and the opening of potassium channels restores the resting membrane potential.
167
What does depolarisation of one patch of membrane cause to the adjacent patches of membrane?
Depolarisation of a patch of membrane causes neighbouring regions of membrane to depolarise and go through the same cycle, as adjacent voltage gated sodium channels are opened.
168
What happens when the action potential reaches the end of a neuron?
When the action potential reaches the end of a neuron it causes vesicles containing neurotransmitters to fuse with the membrane -this releases neurotransmitters, which stimulates a response in a connecting cell.
169
What does restoration of the membrane potential allow voltage gated sodium channels to do?
Restoration of the resting membrane potential allows the inactive voltage gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane.
170
What is used to restore the ion concentration gradients after repolarisation?
Ion concentration gradients are re-established by the sodium potassium pump which actively transports excess ions in and out of the cell.
171
What is the function of the retina?
The retina is the area within the eye that detects light and contains two types of photoreceptor cells: rods and cones.
172
What 2 things form the photoreceptors in animals?
The light sensitive molecule retinal is combined with a membrane protein opsin to form the photoreceptors of the eye.
173
What are the retinal opsin complexes called in rod cells?
In rod cells the retinal opsin complex is called rhodopsin.
174
How does rhodopsin change to photoexcited rhodopsin?
Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin.
175
How is the signal of rhodopsin changing conformation amplified?
A cascade of proteins amplifies the signal.
176
What does photoexcited rhodopsin activate?
Photoexcited rhodopsin activates a G-protein, called transducin.
177
What does transducin activate?
Transducin activates the enzyme phosphodiesterase. (PDE)
178
What does PDE catalyse?
PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP).
179
What does the catalysing of cGMP trigger?
Catalysing of cGMP results in closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina.
180
What allows rod cells to be able to respond to low intensities of light?
A very high degree of amplification results in rod cells being able to respond to low intensities of light.
181
How do cone cells allow us to see colour?
In come cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maximal sensitivity to different wavelengths. (red, green, blue or UV)
182
What is the function of the cytoskeleton?
The cytoskeleton gives mechanical support and shape to cells.
183
What does the cytoskeleton consist of?
It consists of different protein structures including micro tubules, which are found in all eukaryotic cells.
184
What do microtubules do?
Microtubules control the movement of membrane bound organelles and chromosomes.
185
What does cell decision require to happen to the cytoskeleton?
Cell devision requires remodelling if the cytoskeleton.
186
What does formation and breakdown of microtubules involve?
Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin.
187
What do microtubules form which are active during cell devision?
Microtubules form spindle fibres which are active during cell devision.
188
What two phases make up the cell cycle?
The cell cycle consists of interphase and mitotic phase.
189
What does the mitotic phase of the cell cycle involve?
Mitotic phase involves mitosis and cytokinesis.
190
What are the 4 stages of mitosis?
Mitosis consists of prophase, metaphase, anna phase and telophase.
191
What are the 3 parts of interphase?
G1- initial growth phase, protein synthesis occurs.
S- Replication of nuclear DNA
G2- second phase of growth prior to mitosis.
192
What happens during cytokinesis?
The cytoplasm is separated from into two daughter cells.
193
What happens during prophase?
DNA condenses in chromosomes which now consist of sister chromatids. Nuclear membrane breaks down. Microtubules extend from MTOC by polymerisation and attach to chromosomes kinetochores.
194
What happens during metaphase?
Chromosomes are aligned at the metaphase plate (the equator of the spindle)
195
What happens during anaphase?
Separation of sister chromatids and chromosomes are pulled to opposite poles. Pulled apart by spindle microtubules shortened by depolymerisation.
196
What happens during telophase?
Chromosomes decondense and the nuclear membranes are formed around each set of chromosomes.
197
How is progression through the cell cycle controlled?
Progression through the cell cycle is controlled by checkpoints at G1, G2 and metaphase.
198
What are checkpoints?
Checkpoints are mechanisms within the cell that asses the condition of the cell during the cell cycle and halt progression till certain requirements are met.
199
What are cyclin proteins involved in?
Cyclin proteins that accumulate during cell growth are involved in regulating the cell cycle.
200
How do cyclin proteins regulate the cell cycle?
Cyclins combined with active cyclin-dependent kinases (CDKs). These complexes phosphorylase proteins that regulate cell progression till sufficient phosphorylation is reached and progression occurs.
201
What happens at the G1 checkpoint?
At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.
202
What inhibits retinoblastoma protein?
Phosphorylation of G1 cyclin-CDK inhibits the retinoblastoma protein.
203
What happens at the G2 checkpoint?
At the G2 checkpoint, the success of DNA replication and any damage to DNA is assessed.
204
What does DNA damage trigger at the G2 checkpoint.
DNA damage triggers activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death.
205
What does the metaphase checkpoint control?
A metaphase checkpoint controls progression from metaphase to anaphase.
206
What does an uncontrolled reduction in the rate of the cell cycle cause?
An uncontrolled reduction in the rate of the cell cycle may result in degenerative disease.
207
What does an uncontrolled increase in the rate of the cell cycle cause?
An uncontrolled increase in the rate of the cell cycle may result in tumour formation.
208
What is a photo-oncogene?
A photo-oncogene is a normal gene, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene.
209
What is apoptosis?
Apoptosis is programmed cell death.
210
Why is apoptosis essential?
Apoptosis is essential during the development of an organisms to remove cells no longer required as development progresses or during metamorphosis. This is why our hands are not webbed.
211
What triggers apoptosis
Apoptosis is triggered by cell death signals that can be external or internal.
212
Where do external death signal molecules bind to?
External death signal molecules bind to a surface receptor protein and triggers a protein cascade with the cytoplasm.
213
What internal signal cause apoptosis?
An internal death signal resulting from DNA damage causes activation of the p55 tumour suppressor protein.
214
What enzymes cause destruction of the cell?
Both types of death signal result in the activation of caspases (types of protease enzyme) that causes the destruction of the cell.
215
When may cells initiate apoptosis?
In the absence of growth factors.
