Cells And Protiens Flashcards
1
Q
Hazards in the lab include
A
Toxic or corrosive chemicals
Heat or flammable substances
Pathogenic organisms
Mechanical equipment
2
Q
We can identify and control measures to minimise risks and reduce hazards by creating a…..
A
Risk assessment
3
Q
Risk
A
The likely hood of harm arising from the exposure to a hazard
4
Q
Control measure
A
Using appropriate handling techniques, protective clothing and equipment and aseptic techniques
5
Q
Linear dilutions
A
Dilutions differ by an equal interval, for example: 0.1, 0.2, 0.3 ect
6
Q
Log (serial) dilutions
A
Differ by a constant proportion, for example 10^-1, 10^-2, 10^-3 ect
7
Q
Standard curve
A
Some investigations need you to plot known measurements on a graph to then use to determine unknown values
8
Q
Buffers
A
A solution where adding acids or alkalis have very small effects on the ph. This allows ph in a reaction mixture to be kept constant
9
Q
Colorimeters can be used to quantify….
A
Concentration and turbidity
10
Q
Before use the colorimeters need to be…
A
Calibrated to provide a baseline reading
11
Q
Centrifuge
A
Samples are spun at increasingly high speeds, sometimes up to 18,000rpm
This separates substances according to density
More dense components settle to form the pellet whilst less dense components remain in the supernatant
12
Q
Paper and thin layer chromatography
A
Used to separate and identify substances such as amino acids and sugars
The speed that the solute travels along the chromatograph depends on its differing solubility in the solute used
13
Q
Affinity chromatography
A
Used to separate proteins
A solid matrix or gel column is created with specific molecules (usually receptors) bound to it
Soluble target proteins in a mixture, with a high affinity for these molecules become attached to them as the mixture passes down the column
Non target molecules are washed out
14
Q
Gel electrophoresis
A
Used to separate proteins and nucleic acids
The samples are backed into hells which have an electric current running through
Charged molecules will move towards the opposing charge
Smaller molecules travel faster and further than larger molecules
15
Q
Native gels
A
Separate proteins by shape, size and charge and ensure they do not denatured the molecule
16
Q
SDS-PAGE
A
Separates proteins by size by giving all molecules an equally negative charge and denaturing them
17
Q
Isoelectric point (IEP)
A
Used to separate proteins from a mixture
IEP is the specific ph at which a soluble protein has no net charge and will precipitate out of a solution
The solution is buffered to a specific PH, only the proteins that have an IEP of that PH will precipitate
This can be used along with electrophoresis as a proteins stops migrating through the gel at its IEP
18
Q
Immunoassay
A
Used to detect and identify proteins
Uses antibodies with the same specificity known as monoclonal antibodies an antibody specific to the protein antigen linked to a chemical label (or fluorescence or chemiluminescence)
The label is often a reporter enzyme producing a colour change
Can be used to detect diseases
19
Q
ELISA Techniques
A
Enzyme-linked Immunoabsorbent Assay is an analytical technique using antibodies to detect the presence of an antibody within a soloution
There are thre types, direct, in direct and sandwich
20
Q
Direct ELISA
A
The antigen is allowed to bind to the surface of a multi well plate
A primary antibody linked to a reporter enzyme is added to the well and binds to the antigen
21
Q
Indirect ELISA
A
The antigen is allowed to bind to the surface of a multi well plate
A primary antibody is added to the well and binds to the antigen.
A secondary antibody linked to a reporter enzyme is added and binds to the antigen
22
Q
Sandwich ELISA
A
A capture antibody is allowed to bind to the surface of a multi well plate
The antigen is added and allowed to bind to the capture antibody
A primary antibody binds to the antigen
A secondary antibody linked to a reporter enzyme is added to the well and binds to the primary antibody
23
Q
Western Blotting
A
Used after SDS-PAGE Electrophoresis
Once the proteins are separated they are transferred or blotted onto a solid medium
Proteins can be identified by ELISA
24
Q
Bright field microscopy
A
Used to observe whole organisms, parts of organisms, thin sections, dissected tissue or individual cells
25
Fluorescence microscopy
Uses specific fluorescent labels to bind to and visualise certain molecular structures within cells or tissues
26
Aseptic technique
Procedures used in laboratories to reduce contamination as well as the unwanted growth or spread of micro-organisms
Eg sterilisation by heat or chemical
27
Microbial culture
A method of multiplying microorganisms by letting them reproduce in a culture medium under controlled laboratory conditions
Can be started using an inoculum of microbial cells on an agar medium or broth
28
Animal cells are grown in....
A medium containing proteins called growth factors from serum. These promote cell growth and proliferation
These are essential
29
Primary cell lines can divide a limited number of times whereas tumour cell lines....
Can preform unlimited divisions
30
Serial dilution
Allows the number of colonies on solid media to be of a low enough density to be counted
31
Heamocytometer
Specialised microscope cells used to estimate cell numbers in liquid culture
32
Vital staining
Allows a count on living cells only
| Dead cells will not absorb the stain
33
The proteome
The entire set of proteins that is , or can be, expressed by a certain genome, cell, tissue, or organism at a certain time
34
More than one protein can be produced from a single gene due to....
Alternative gene splicing
35
Non coding RNA genes
Genes that do not code for proteins
| Transcribed to produce tRNA, rNA, and RNA molecules that control the expression of other genes
36
The set of proteins expressed by a given cell type can vary over...
Time and under different conditions
37
4 factors affecting the set of proteins expressed by a given cell type are:
Metabolic activity of the cell
Cellular stress
Response to signalling molecules
Diseased vs healthy cells
38
The system of internal membranes in Eukaryotic cells ....
Increase the total area of the membrane
39
Because of their size, Eukaryotes have a relatively small...
Surface area to volume ratio
40
The plasma membrane of eukaryotic cells is too small to...
Carry out all the vital functions of the cell
41
Name 13 parts of the cell
```
Cell membrane
Golgi apparatus
Golgi vesicles
Nucleus
Lysosome
Ribosome
Microtubules
Pinocytotic vesicles
Endoplasmic reticulum
Centrioles
Vacuole
Mitochondria
Smooth endoplasmic reticulum
```
42
Endoplasmic reticulum
Forms a network of membrane tubules continuous with the nuclear membrane
43
Golgi apparatus
A series of flattened membrane disks
44
Lysosomes
Membrane bound organelles containing a variety of hydrolyses that digest proteins, lipids, nucleic acids and carbohydrates
45
Vesicles
Transport materials between membrane compartments
46
Parts of the cell involved in synthesis of membrane components
Ribosomes
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
47
Lipids and proteins are synthesised in the...
Endoplasmic reticulum
48
What is the difference between rough endoplasmic reticulum and smooth endoplasmic reticulum?
RER has ribosomes on its cytosolic face while SER does not
49
Lipids are synthesised in...
The SER and inserted into its membrane
50
The synthesis of all proteins begins in the...
Cytosolic ribosomes
51
The synthesis of cytosol proteins is completed in the...
Cytosolic proteins, these proteins remain in the cytosol (liquid part of cytoplasm)
52
Transmembrane proteins
Carry a signal sequence which halts translation and directs the ribosome synthesising the protein to dock with the ER forming RER
53
Signal sequence
A short stretch of amino acids at one end on the polypeptide that determines the eventual location of a protein in a cell
54
Stage one of synthesis of membrane components by RER
Proteins are synthesised by ribosomes in the cytoplasm
55
Stage two of synthesis of membrane components by RER
A signal protein (SRP) from the membrane binds to the ribosome and stops translation
56
Stage three of synthesis of membrane components by RER
The SRP binds to the receptor which directs the ribosome to attach to the endoplasmic reticulum forming the RER
57
Stage four A of synthesis of membrane components by RER
Translation restarts and the protein is now inserted into the proteins of the ER
58
Stage four B of synthesis of membrane components by RER
Once translation is fixed the ribosome detaches
59
Once the proteins in the RER, they are ....
Transported by the vesicles that bud off from the ER and fuse with the Golgi apparatus
60
As proteins move through the Golgi apparatus they undergo...
Post translational modification
61
The major modification of post translational modification is...
The addition of carbohydrate groups
62
Molecules move through the Golgi discs in...
Vesicles that bud off from one disc and fuse to the next one in the sack
63
Enzymes catalyse the addition of various sugars in multiple steps to form
Carbohydrates (glyco proteins)
64
Vesicles that leave the Golgi apparatus take proteins to the...
Plasma membrane and lysosome
65
What do vesicles move along to other membranes and fuse with them within the cell
Microtubules
66
Secreted proteins are translated in the ... way
Ribosomes on the RER and enter it’s lumen
67
Examples of secreted proteins
Peptide hormone
| Digestive hormone
68
Describe the secretory pathway
The proteins move through the Golgi apparatus and are then packed into secretory vesicles. These vesicles move to fuse with the plasma membrane, releasing the proteins out of the cell
69
Many secreted proteins are synthesised as inactive proteins and require....
proteolytic cleavage to produce active proteins
70
Proteolytic cleavage
Another type of post translational modification
71
Give examples of secreted proteins that require proteolytic cleavage to become active
Digestive enzymes
| Insulin
72
Describe the structure of proteins
Polymers of amino acid monomers
| Amino acids are linked by peptide bonds to form polypeptides
73
Amino acids have the same basic structure but differ in...
The R groups present
74
R groups vary in...
Size, shape, charge , hydrogen bonding capacity and chemical reactivity
75
Amino acids are classified according to their R groups, like:
Basic (positively charged)
Active (negativity changed)
Polar
Hydrophobic
76
The wide range of functions carried out by proteins results from the diversity of...
Amino acid R groups
77
Primary structure
The sequence in which the amino acids are synthesised into the polypeptide
78
Hydrogen bonds along the backbone of the protein strand results in...
Regions of secondary structure
79
Some secondary structures of proteins are...
Alpha helices
Parallel or anti parallel beta pleated sheets
Turns
80
A polypeptide folds into a tertiary structure. This conformation is stabilised by ...
Interactions between R groups
81
The tertiary structure of polypeptides is stabilised by interactions between R groups such as..
```
Hydrophobic interactions
Ionic bonds
London dispersion forces
Hydrogen bonds
Disulphide bridges (consistent bonds between R groups containing sulphur)
```
82
Quaternary structure
Exists in proteins with two or more connected poly peptide subunits
Describes the spread arrangement of the subunits
83
Prosthetic group
Ia nonpolar unit tightly bound to a protein and necessary for it to function for example the molecule haemoglobin
84
Haemoglobin
Iron containing oxygen transporting protein present in the red blood cells of almost all vertebrates
85
The ability of haemoglobin to binds to oxygen is dependent upon...
The non protein haem group
86
Interactions of the R groups can be influenced by
Temperature and pH
87
Increasing the temperature of a protein...
Disrupts the interactions that hold the protein and shape the protein begins to unfold eventually becoming denatured
88
The charges on acidic and basic R groups are affected by pH. As pH increases or decreases from the optimum....
The normal ionic interactions between charged groups are lost which gradually changes the confirmation of the protein until it becomes denatured
89
Ligand
A substance that can bind to a protein
90
R groups not involved in protein folding can allow...
Bonding to Ligands. The binding sites will have a complimentary shape and chemistry to the ligand
91
As a ligand binds to a protein binding site the confirmation of the protein changes this change in confirmation causes a....
Functional change in the protein
92
Allosteric
Interactions which occur between spatially distinct sites
93
The binding of a substrate molecule to one active site of an allosteric enzyme increases...
The affinity of the other active sites for Binding of subsequent substrate molecules
94
The activity of allosteric enzymes can vary greatly with...
Small changes in the substrate concentration
95
Many allosteric proteins consist of
Multiple subunits which means they have a quaternary structure
96
Allosteric proteins with multiple subunits sure cooperativity and binding. what is this?
Changes in binding at one subunit alter the infinity of the remaining subunits
97
Allosteric enzymes contain a second type of site called...
An allosteric site
98
Modulators
Regulate the activity of the enzyme when they binds to the allosteric site
99
What is the effect of a modulator
The confirmation of the enzyme changes and this alters the affinity of the active site for the substrate
100
Positive modulators
Increase the enzymes affinity for the substrate (activation)
101
Negative modulators
Decrease the enzymes affinity for the substrate (inhibitors)
102
Give an example of a molecule that shows cooperativity
Haemoglobin
103
What combination of shift of pH and temperature will lower the affinity of haemoglobin for oxygen
A decrease in pH and an increase in temperature
104
Reducing the binding of oxygen in actively respiring tissue to haemoglobin will promote
Increased oxygen delivery to tissue
105
The addition of removal of phosphate can cause...
Reversible confirmational changes in proteins this is a common form of post-translational modification
106
Protein kinases
Catalyse the transfer of aphosphate group to other proteins
107
Which phosphate of ATP is transferred to specific R groups in the protein
Terminal phosphate
108
Protein phosphaleses
Catalyse the reverse reaction to protein kinases
109
Phosphorylation
Beings about confirmational changes which can affect. the activity of many cellular proteins such as enzymes and receptors are regulated in this way. some proteins are activated by phosphorylation but others are inhibited
110
Adding A phosphate group adds...
Negative charges.
| Ionic interactions in the unphosphorylated protein can be disrupted a new one is created
111
Fluid mosaic model
A model that describes the structure of a cell membrane
112
Name parts of a cell membrane
```
Integral glycoprotein
Carbohydrates
Membrane channel
Peripheral protein
Integral protein
```
113
What holds Integral membrane proteins in the phospholipid bilayer
Regions of hydrophobic R group allow strong hydrophobic interact that hold them in
114
Integral membrane proteins
Interact extensively with the hydrophobic region of membrane phospholipids
Some integral membrane proteins are transmembrane proteins which mean they span the entirety of the cell
115
Peripheral membrane proteins
Peripheral membrane proteins have hydrophilic R group on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions. Many peripheral proteins interact with the surface of integral membrane proteins
116
Phospholipid bilayer
The phospholipid bilayer is a barrier to ions and most unchanged polar molecules
Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion
117
Transport proteins
Facilitated diffusion is the passive transport of substances across membrane through specific transmembrane proteins
118
To perform specialised functions, different cell types have different....
Channels and transporter proteins
119
Channels
Multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane
120
Most channel proteins in plants and animals are highly selective. This means
They let very few types of molecules pass through
121
Some channel proteins are gated, this means...
They change conformation to allow or prevent diffusion
122
Ligand gated channels
Controlled by the binding of signal molecules
123
Voltage gated channels
Controlled by changes in ion concentration
124
Transporter proteins
Bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
125
Transporters alternate between two conformation so that...
The binding site for a solute is sequentially exposed on one side of the bilayer, then the other
126
Active transport
Uses pump proteins that transfer substances across the membrane against their concentration
127
Pumps that mediate active transport
Transporter proteins coupled to an energy source
128
What is required for active transport
Metabolic energy
129
Some active transport proteins hydrolyse ATP directly to provide...
The energy for conformational change required to move substances across the membrane
130
ATPases
The enzymes used to hydrolyse ATP for active transport
131
For a solute carrying a net charge the concentration gradient and the electrical potential difference (voltage) ...
Combine to form the electrochemical gradient that determines the transport of the solute
132
The electrochemical gradient
Forms due to the net positive charge outside the cell and the net negative charge inside the cell
133
Membrane potential
(An electrical potential difference)
| Created when there is a difference in electrical charge on the two sides of the membrane
134
Where does the energy for the sodium potassium pump come From and what is used for?
The hydrolysis of ATP
| To establish and maintain ion gradients
135
Sodium potassium pump
Transports ions against a steep concentration gradient using energy from ATP hydrolysis
Transports sodium ions out of the cell a potassium ions into the cell
136
Describe the first stage of the sodium potassium pump
The pump has high affinity for sodium ions inside the cell
| Binding occurs and the pump is phosphorylated by ATP
137
Describe the second stage of the sodium potassium pump
The confirmation of the protein changes and the affinity for sodium ions decreases. This means the sodium ions are released outside of the cell
138
Describe the third stage of the sodium potassium pump
The potassium ions bind outside the cell
139
Describe the fourth stage of the sodium potassium pump
Dephosphorylation occurs and the conformation of the protein changes
140
Describe the fifth stage of the sodium potassium pump
Potassium ions are taken into the cell and the affinity returns to start
141
How is the electrical and chemical gradient established in the sodium potassium pump
For each ATP hydrolysed, three sodium ions are transported out of the cell and two potassium ions are transported into the cell
142
The sodium potassium pump is found in most animal cells, accounting for...
...a high proportion of the basal metabolic rate in many organisms
143
What is the role of the sodium potassium pump in the small intestine
The sodium gradient created by the sodium potassium pump drives the active transport of glucose
144
Describe the process of the sodium potassium pump in the small intestine
In intestinal epithelial cells the sodium potassium pump generates a sodium ion gradient across the plasma membrane.
The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time in the same direction
Sodium ions enter the cell down their concentration gradient.
The simultaneous transport of glucose pumps glucose into the cell against its concentration gradient
145
Hydrophobic
Molecules that are seemingly repelled by a mass of water.
| These molecules are known as non-polar
146
Hydrophobic signalling molecules
Can diffuse directly through the phospholipid bilayer of membranes, and so bind to the intercellular receptors. These receptors are transcription factors
147
Transcription factors
Protein that when bound to DNA can either stimulate or inhibit initiation of transcription
148
Examples of hydrophobic signalling molecules
Oestrogen
| Testosterone
149
Steroid hormones bind to...
Specific receptors in the cytosol or the nucleus
150
What happens after a steroid hormone bonds to a receptor
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and effects gene expression
151
Hormone response elements (HRE’s)
The hormone receptor complex of steroid hormones binds to this specific DNA sequences
Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes
152
Hydrophilic
A molecule that is attracted to water molecules and tends to be dissolved by water
also known as a polar molecule
153
Hydrophilic signal molecules
Binds to transmembrane receptors and do not enter the cystol
| examples of hydrophilic extracellular signalling molecules are peptide hormones and neurotransmitters
154
Transmembrane receptors change confirmation when...
The ligand binds to the extracellular face
155
The signal molecule does not enter the cell but
Is transduced across the plasma membrane
156
Transduction
A process by which a chemical or physical signal is transmitted through a cell by a series of molecular events resulting in a cellular response
157
Transmembrane receptors
Act as signal transducers by converting the extracellular ligand binding event into intercellular signals which alters the behaviour of the cell
158
Transduced hydrophilic signals
Involve G proteins or cascades of phosphorylation by kinase enzymes
159
G-proteins
Really signals from activated receptors
160
Activated receptors
Receptors that have bound a signal molecule to target the proteins such as enzymes and ion channels
161
Phosphorylation cascades
allow more than one intercellular signalling pathway to be activated involve a series of events with one Kinase activating the next in the sequence and so on
phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event
162
What happens when insulin binds to its receptor hormone
The binding of the peptide hormone insulin to its receptor results in an intercellular signalling cascade that triggers recruitment of GLUT 4 glucose transporter proteins to the cell membrane of fat and muscle cells
163
Step one of the binding of insulin
Binding insulin to its receptor causing a conformation change that triggers phosphorylation of the receptor
164
Step two of the binding of insulin
The phosphorylation of the receptor starts a phosphorylation cascade inside the cell
165
Step three of the binding of insulin
This phosphorylation eventually leads to GLUT 4- containing vesicles being transported to the cell membrane
166
Diabetes mellitus can be caused by...
Failure to produce insulin (type 1) or loss of sensitivity (type 2)
167
Type 2 diabetes is generally associated with...
Obesity
168
How does exercise help treat type 2 diabetes
Exercise triggers recruitment of GLUT 4, so can improve the uptake of glucose to fat and muscle cells
169
What is the cause of type 1 diabetes
Body fails to produce insulin
170
What is the cause of type 2 diabetes
Receptors do not respond to insulin
171
What is the treatment of type 1 diabetes
Daily insulin injections
172
What is the treatment of type 2 diabetes
Controlled diet and exercise
173
Nerve impulse
A signal transmitted along a nerve fibre
174
Resting membrane potential
A state where there is no net flow of ions across the membrane
175
The transmission of a nerve impulse requires....
Changes in the membrane potential of the neurons plasma membrane
176
Action potential
A wave of electrical excitation along a neurons plasma membrane
177
Neurotransmitters
Chemicals that transmit a signal across a synapse (a gap between two neurons)
178
Neurotransmitters initiate a response by...
Binding to their receptors (ligand gated ion channels) at a synapse
179
Name things involved in a nerve impulse
```
Neurotransmitter
Neurotransmitter transporter
Synaptic vesicle
Voltage gated Ca2+ channel
Post synaptic destiny
Receptor
Axon terminal
Synaptic cleft
Dendrite
```
180
Depolarisation
A sudden change in membrane potential, usually from a relatively negative to positive change
181
Depolarisation of the plasma membrane as a result of the entry of positive ions triggers...
The opening of voltage gated sodium channels and further depolarisation occurs
182
Inactivation of the sodium channels and the opening of potassium channels restores...
The resting membrane potential
183
Binding of a neurotransmitter triggers the opening of
Ligand gated ion channels at a synapse
184
Fast chemical synapses contain...
Inotropic receptors
185
Ion movement occurs when there is...
Depolarisation of the plasma membrane
186
If sufficient ion movement occurs, and the membrane is depolarised Beyond a threshold value...
The opening of the voltage gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient.
This leads to a rapid and large change in membrane potential.
A short time after the opening, the sodium channels become inactivated voltage gated potassium channels, then open to allow potassium ions to move out of the cell to restore the resting membrane potential
187
What is the first stage of the restoration of Resting membrane potential
Stimulus starts the rapid change in voltage or action potential
This much reach above a threshold voltage to start membrane depolarisation
188
What is the second stage of the restoration of Resting membrane potential
Depolarisation is caused by a rapid rise in membrane potential opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions
189
What is the third stage of the restoration of Resting membrane potential
Membrane depolarisation results from rapid sodium channel inactivation as well as a large efflux of potassium ions resulting from activated potassium channels
190
What is the fourth stage of the restoration of Resting membrane potential
Hyper polarisation is a lowered membrane potential caused by the efflux of potassium ions and the closing of the potassium channels
191
What is the fifth stage of the restoration of Resting membrane potential
Resting stage is when membrane potential returns to the resting voltage that occurred before stimulation occurred
192
Depolarisation of a patch of membrane causes neighbouring regions of membrane to..
Depolarise and go through the same cycle, as adjacent voltage gated sodium channel are opened
193
When the action potential reaches the end of the neuron it causes....
Vesicles containing neurotransmitters to fuse with the membrane, this releases neurotransmitter which stimulates a response in a connecting cell
194
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
195
Ion concentration gradients are re-established by ...
The sodium potassium pump which activity transports ions in and out of the cell
196
Following repolarisation the sodium and potassium ion gradients are...
Reduced
197
The sodium potassium pump restores the...
Sodium and potassium ions back to resting potential levels
198
Name parts of the eye
```
Choroid
Retina
Fovea
Optic nerve
Ciliary body
Iris
Lense
Pupil
Cornea
```
199
Retina
The area of the eye that detects light and contains two types of photo receptor: rods and cones
200
Rods
Function in dim light but do not allow colour perception
201
Cones
Responsible for colour vision and only function in bright light
202
How are the photo receptors in animals formed
The light sensitive molecule retinal is combined with the protein ops in
203
In rod cells the retinal-Opsin complex is called
rhodopsin
204
Retinal absorbs a photon of light and...
Rhodopsin changes conformation to photoelectrical rhodopsin. A cascade of proteins amplifies the signal
205
A single Photo excited rhodopsin actives...
Hundreds of molecules of G-protein called transducin
206
A Transducin molecule activates
A single molecule of the enzyme phosphodiesterase (PRE)
207
PDE catalyses...
The hydrolysis of a molecule called cyclic GMP (cGMP)
208
Each active PDE breaks down...
Thousands of cGMP molecules per second
209
The reduction in cGMP concentration as a result of its hydrolysis affects...
The function of the ion channels in the membrane of the rod cells, resulting in their closure
210
The closure of ion channels the the membrane of rod cells triggers...
Nerve impulses in nerves in the retina
211
A very high degree of amplification results in...
Rod cells being able to respond to low intensities of light
212
In cone cells, different forms of ops in combine with retinal to give different...
Photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, blue, green and uv
213
Describe step one of a nerve impulse in the vertebrae eye...
Light stimulation of rhodopsin leads to activation of a G-protein (transduction)
214
Describe step two of a nerve impulse in the vertebrae eye...
Activated G protein activate cGMP
| Phosphodiesterase (PDE)
215
Describe step three of a nerve impulse in the vertebrae eye...
PDE hydrolyses cGMP, reducing its concentration
216
Describe step four of a nerve impulse in the vertebrae eye...
This leads to closure of the Na+ channels
217
Cytoskeleton
A complex network of protein filaments that gives mechanical support and shape to cells
218
The cytoskeleton consists of
Different protein structures including microtubules which are found in all eukaryotic cells
219
Microtubules
Hollow cylinder is composed of the protein tubulin
| We they radiate from the Microtubule organising centre (MTOC) (centrosome)
220
Microtubules control
The movement of membrane-bound organelles and chromosomes
221
Microtubules also form
The spindle fibers that are active during cell division
| This means that the cytoskeleton needs to be remodelled during cell division
222
The formation and breakdown of microtubules involves
Polymerisation and depolymerisation of tubulin
223
The cell cycle consists of
Interphase and mitotic phase (M phase)
224
Which is shorter than the mitotic phase or the interphase
The mitotic phase
225
Interphase involves
Growth and DNA synthesis
226
Name the stages of interphase
G1, S, G2
227
G1
Growth phase
228
S
The phase or DNA is replicated (synthesis)
229
G2
Second growth phase
230
The mitotic phase involves
Mitosis and cytokinesis
231
Mitosis
The separation of chromosomal material by the spindle microtubules
232
Cytokinesis
Separation of the cytoplasm into two daughter cells
233
Mitosis consists of
Prophase
Metaphase
Anaphase
Telophase
234
Prophase
DNA condenses into chromosomes, each consist of two sister chromatids.
nuclear membrane breaks down spindle microtubules extend from the MTOC by polymerisation and attach to chromatids via their kinetochores in the centromere region
235
Metaphase
Chromosomes are aligned the metaphase plate
236
Anaphase
As spindle microtubules shorten by depolarisation, sister chromatids are separated and the chromosomes are pulled to opposite poles
237
Telophase
The chromosomes decondense and nuclear membranes form around them
238
Checkpoints
Mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met
239
Cyclin proteins
Accumulate during cell growth and are involved in regulating the cell cycle
240
Cycling combine with and activate....
Cyclin dependent kinases (CDKs)
241
Active cyclin-CDK complexes...
Phosphorylate proteins that regulate progression through the cycle. If sufficient for formulation is reached progression occurs
242
G1 checkpoint
Retinoblastoma protein acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.
Phosphorylation by G1 cyclin inhibits the retinoblastoma protein. This allows transcription of genes that code for proteins needed for DNA replication so cells progress from G1 to S phase
243
G2 checkpoint
The success of DNA replication and any damage to DNA is assessed.
Do you any damage triggers the activation of several proteins including PS3 That can stimulate DNA repair, Arrest the cell cycle or cause cell death.
If this checkpoint passes the sale progresses from G2 to M phase
244
Metaphase checkpoint
Controls progression from metaphase to anaphase
Here progression is halted until the chromosomes are Aligned correctly on the metaphase plate and attached to the spindle microtubules
245
I don’t controlled reduction in the rate of the cell cycle may result in
Degenerative disease for example Alzheimer’s disease
246
An uncontrolled increase in the rate of the cell cycle may result in
Tumour formation
247
Proto-oncogenes
And normal gene usually involved in the control of cell growth and division which can mutate to form a tumour promoting oncogene
248
Apoptosis
The death of cells which occurs as a normal and controlled part of an organisms growth and development
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Apoptosis is triggered by
Cell death signals that can be external or internal
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External death signals
The production of this signal molecules from lymphocytes as an example of an external death signal. the death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm
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Internal death signals
Do you any damage is an example of an internal death signal
| And internal death signal resulting from DNA damage causes the activation of PS3 tumour suppressor protein
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Both types of death signal result in
The activation of caspases (Types of protease enzyme) That cause the destruction of the cell
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Apoptosis is essential during the development of an organism to remove....
Sales no longer required as development progresses or during metamorphosis
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Cells may initiate apoptosis in the absence of
Growth factors
