Unit 1- Part 2 Flashcards
Membrane Proteins, Signalling and Nerve Impulse transmission, Cell Cycle, Control of Cell Cycle and Apoptosis (170 cards)
1
Q
What are cell membranes composed of?
A
Proteins embedded within a phospholipid bilayer
2
Q
The structure of the cell membrane can be described as what?
A
‘Fluid mosaic model’
3
Q
What are phospholipids composed of?
A
Hydrophilic Heads (water-loving!) Hydrophobic Tails (water-hating!)
4
Q
Membrane proteins can either be …… or ……… in the membrane
A
Integral
Peripheral
5
Q
What allow strong hydrophobic interactions with the hydrophobic regions of membrane phospholipids?
A
regions of hydrophobic R groups
6
Q
What do the strong hydrophobic interactions with the hydrophobic regions of membrane phospholipids hold?
A
Integral membrane proteins within the phospholipid Bilayer.
7
Q
Some integral proteins are what?
A
Transmembrane proteins spanning the entire width of the membrane
8
Q
What do peripheral membrane proteins have on their surface and how are they bound to the surface of the membrane?
A
Hydrophilic R groups
Ionic and hydrogen bond interactions
9
Q
Many peripheral proteins interact with what?
A
Integral membrane proteins
10
Q
What are the 3 major roles of membrane proteins?
A
Movement of molecules across the membrane
Transmission of extracellular signals ie. Signal transduction
Detecting and amplifying stimuli photoreceptor protein system
11
Q
The phospholipid bilayer is semi-permeable what does this mean?
A
It only lets certain molecules into and out of the cell
12
Q
What does the membrane act as a barrier to?
A
Ions and large polar uncharged molecules
13
Q
Some small molecules such as oxygen and CO2 pass through the membrane by what?
A
Diffusion
14
Q
Do hydrophobic molecules pass through the membrane? (Oxygen and Carbon Dioxide)
A
Yes
15
Q
Small uncharged polar molecules (water and glycerol) can they pass through the membrane?
A
Yes
16
Q
Large uncharged polar molecules and Ions do pass through the membrane?
A
No
17
Q
What is facilitated diffusion?
A
Passive transport of substances across the membrane through specific transmembrane proteins
18
Q
Transmembrane proteins are what?
A
Channels or transporter proteins
19
Q
To perform specialized functions, different cell types have different …….. and …….. proteins?
A
Channels and transporter proteins
20
Q
Most channel proteins in animal and plant cells are what?
A
Highly selective
21
Q
Describe channel proteins
A
Proteins with multiple subunits arranged to form water-filled pores that extend across the membrane.
22
Q
Channel proteins can be what or what
A
Gated or ungated
23
Q
What is an example of an ungated channel protein?
A
Aquaporins
24
Q
Gated channel proteins change conformation to do what?
A
allow or prevent diffusion
25
What are the 2 types of gated channel proteins
Ligand-gated
| Voltage-gated
26
Describe Ligand-gated channels
Ligand-gated channels proteins are controlled by the binding of specific signal molecules and allow the passage of solutes by altering conformation.
27
Describe Voltage-gated channels
Voltage-gated channels are controlled by changing ion channels
28
Give an example of an ion channel?
Sodium channels
29
What do transporter proteins bind to and why do they undergo a conformational change?
Specific substances to be transported.
To transfer the solute across the membrane.
30
Why do transporter proteins alternate between 2 different conformations?
So that the binding site for a solute is sequentially exposed on one side of the bilayer then the other.
31
What is active transport?
When molecules move against the concentration or electrochemical gradient
32
What is passive transport?
With the concentration gradient or electrochemical gradient (facilitated diffusion)
33
What type of transport uses pump proteins that transfer substances across the membrane against the concentration gradient?
Active transport
34
What are the pumps that mediate active transport?
transporter proteins coupled with an energy source
35
What is required for active transport?
ATP
36
Some active transport proteins hydrolyse ATP directly to do what?
Provide the energy for conformation changes required to move substances across the membrane
37
What are proteins which hydrolyse ATP called?
ATPases
38
When is a membrane potential created?
when there is a difference in electrical charge on the 2 sides of the membrane
39
For a solute that carries a net charge, the concentration gradient and the electrical potential difference combine to form what?
the electrochemical gradient that determines the transport of the solute
40
Ion pumps such as .................... use energy from the hydrolysis of ATP to establish and maintain these ions gradient.
Sodium pottasium Pump
41
How does the sodium-potassium pump transport using energy from ATP?
against a Steep concentration gradient
42
Describe the stages of the sodium-potassium pump
1. The pump has a high affinity for sodium ions inside the cell. 3 sodium ions bind.
2. Binding stimulates phosphorylation by ATP. Phosphorylation causes conformation change.
3. The affinity for sodium ions decreases. Sodium ions are released outside of the cell.
4. 2 potassium ions bind outside of the cell, triggers dephosphorylation (release of a phosphate group).
5. Loss of phosphate causes a conformation change.
6. Potassium ions are taken into the cell and affinity returns to start.
43
For each ATP hydrolysed, how many sodium ions are transported out of the cell and how many potassium ions are transported into the cell.
Sodium- 3
| Potassium-2
44
For each ATP hydrolysed, three sodium ions are transported out of the cell and two potassium ions are transported into the cell. What does this establish?
both concentration gradients and an electrical gradient.
45
The sodium-potassium pump is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms. What percentage in humans
Up to 25%
46
The sodium-potassium pump is important in doing what?
Generating and maintaining ion gradients.
47
The sodium-potassium pump is important in generating and maintaining ion gradients which are key to many processes in the body. What are the two examples?
Generating an ion gradient for glucose symport in the small intestine
Generation and long term maintenance of ion gradient for resting potential in neurons
48
Describe the generation of an ion gradient for the glucose symport in the small intestine.
In intestinal epithelial cells the sodium-potassium pump generates a sodium ion gradient across the plasma membrane.
The sodium gradient caused by the sodium-potassium pump drives the active transport of glucose.
This allows glucose to be absorbed from the small intestine into the bloodstream.
The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time and 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.
49
How do multicellular organisms achieve coordination?
Through extracellular signaling molecules, receptors, and responses.
50
Describe in as much detail as you can- Hormones.
Chemical messengers
Produced by the endocrine glands and travel to the bloodstream to target tissues.
Target tissues have receptors which are complementary to a specific hormone
51
Multicellular organisms signal between cells using extracellular molecules. Name some extracellular molecules.
Steroid hormone
Peptide Hormone
Neurotransmitters
52
What are receptor molecules of target cells?
Proteins with a binding site for a specific signal molecule
53
Binding of a receptor molecule to target cell changes what?
Conformation of receptor initiating a response within the cell.
54
Different cell types produce specific signals that can only be detected and responded to by cells with what?
the specific receptor.
55
Describe the extracellular signalling pathway.
Signalling cells
Specific signalling molecules released as a result of a change in internal state
Signalling molecules carried to target cells
Target cells
Signalling molecule binds to receptor and causes conformational change and is linked to a change in the internal state of the cells (cell response)
56
In multicellular organisms, different cell types may show a tissue-specific response to the same what?
Signal
57
Why would Signalling molecules have different effects on different target cell types?
Due to differences in the intracellular signalling molecules and pathways that are involved
58
Different cell types may show a specific and different tissue response to the same signal. True or False
True
59
Describe steroid hormones and how they interact with the membrane.
Steroid hormones are lipophilic (fat-loving) – meaning they can freely diffuse across the plasma membrane of a cell. They bind to receptors in either the cytoplasm or nucleus of the target cell. Examples are; oestrogen and testosterone.
60
Describe peptide hormones and how they interact with the membrane.
Peptide hormones are hydrophilic and lipophobic (fat-hating) – meaning they cannot freely cross the plasma membrane. They bind to receptors on the surface of the cell. Examples are, insulin, ADH and glucagon.
61
Describe neurotransmitters and what they do.
Neurotransmitters are also chemical messengers. They transmit their messages over much shorter distances than hormones can. Neurotransmitters carry messages across a synapse.
62
What is a hydrophobic signalling molecule and what can it do?
A hydrophobic signalling molecule is able to directly diffuse through the phospholipid bilayers of membranes. Once inside the cell it can bind to an intracellular receptor.
63
The receptors for hydrophobic signalling molecules are called what?
Transcription Factors
64
What are transcription factors
Transcription factors are proteins that when bound to DNA can either stimulate or inhibit the initiation of transcription.
65
Steroid hormones are examples of what?
Hydrophobic signaling molecules.
66
Give examples of steroid hormones
Oestrogen and testostrerone
67
Describe the movement of steroid hormones in the cell
They can pass through cell membranes and bind to specific receptors in the cytosol or the nucleus.
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression.
68
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression. What are the names of these sites on DNA?
Hormone response Elements
69
What does the binding to the hormone response element do?
influences the rate of transcription, each steroid hormone affects the gene expression of many different genes.
70
Hydrophilic Molecules are unable to pass through the membrane. Where do they bind to instead?
Transmembrane receptor molecules on the surface of the cell and do not enter the cytosol
71
Name some examples of hydrophilic extracellular signal molecules.
Peptide hormones and neurotransmitters
72
Describe how Hydrophilic signals work
1. A ligand (signalling molecule) binds the transmembrane receptor.
2. Receptors change conformation (the signal molecule does not enter the cell) but the signal is transduced across the plasma membrane.
3. Transmembrane receptors act as signal transducers by converting extracellular ligand-binding event into specific intracellular signals, which alters the behaviour of the cell.
73
What does hydrophilic signal transduction involve
Transduction involves a series of reactions that occur inside the cell (intracellularly) through a signal transduction pathway.
74
What do transduced hydrophilic signals often involve?
G-proteins or cascades of phosphorylation by kinase enzymes.
75
What do G-proteins do?
G-proteins relay signals from activated receptors (receptors that have bound a signaling molecule) to target proteins such as enzymes and ion channels.
76
What do phosphorylation cascades allow?
Allow more than one intracellular signaling pathway to be activated.
77
What do phosphorylation cascades involve?
Involve a series of events with one kinase activating the next in the sequence and so on.
78
Phosphorylation cascades can result in what?
phosphorylation of many proteins as a result of the original signaling event.
79
Insulin is what type of hormone made up of short chains of amino acids?
Peptide
80
Why is insulin required?
To maintain normal blood sugar levels
81
Binding of insulin to its receptor results in an intracellular signalling cascade that triggers the recruitment of what?
Glut-4
82
Describe what Glut-4 transporters do?
Transport glucose to fat and muscle cells
83
What is type 1 diabetes?
failure to produce insulin
84
What is type 2 diabetes?
loss of receptor function
85
How does exercise improve type 1 diabetes?
triggers the recruitment of Glut-4, therefore improve the uptake of glucose to fat and muscle cells
86
Describe how Glut-4 is released
Binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor.
This starts a phosphorylation cascade inside the cell, which eventually leads to GLUT4-containing vesicles being transported to the cell membrane to increase active GLUT4 activity in the membrane.
This cascade results in a lowering of blood glucose levels.
87
Membrane proteins have 3 major roles what are they?
Movement of molecules across membranes
Transmission of extracellular signals, ie signal transduction
3. Detecting and amplifying stimuli: photoreceptor protein systems.
88
What is the electrical potential difference?
The electrical potential difference is the difference in voltage between the inside and the outside of the cell
89
What is the electrical potential difference caused by?
It is caused by varying concentrations of charged molecules.
90
What is the membrane potential?
Membrane potential is the difference in electric potential between the interior and the exterior of a biological cell
91
What is the resting potential?
The resting membrane potential is where there is no net flow of ions across the membrane.
92
What is the typical resting potential?
-70mv
93
What does the transmission of a nerve impulse require?
Changes in the membrane potential of the neurons plasma membrane
94
What does the transmission of a nerve impulse involve?
a wave of depolarisation of the resting potential of a neuron
95
What is the meaning of depolarisation?
Depolarisation is a change in the membrane potential to a less negative value inside.
96
What does depolarisation result from?
Depolarisation results from a wave of electrical excitation along a neuron’s plasma membrane.
97
What is an action potential?
a wave of electrical excitation along a neuron’s plasma membrane.
98
Draw an action potential graph.
Include a rising limb of depolarisation, repolarisation falling limb and hyperpolarising returning to resting potential
99
What are neurotransmitters?
Chemical messengers
100
In nerve transmission how do neurotransmitters initiate a response?
Binding to their receptor in the synapse
101
How do neurotransmitters cause the depolarisation of the plasma membrane?
Neurotransmitter receptors are ligand-gated ion channels. These open in response to binding and allow entry of positively charged ions.
Therefore, this causes depolarisation of the plasma membrane.
102
What is the threshold frequency of a neuron?
The threshold value controls whether or not the incoming stimuli are sufficient to generate an action potential it is the minimum .
103
If sufficient ion movement occurs and the threshold value is met what opens in the neuron?
Voltage-gated sodium channels
104
When sodium channels are opened. Sodium ions enter down their electrochemical gradient- this leads to rapid what?
Change in membrane potential and further depolarisation.
105
What does the synapse allow?
Transmission of messages from 1 neuron to another
106
Describe the stages of a nerve impulse.
Neurotransmitter molecules cause depolarisation of the resting potential.
Neurotransmitter molecules act as ligands and bind to a ligand-gated ion channel at synapse.
This opens a ligand-gated Na + channel in the neuron membrane and Na+ ions diffuse into the neuron.
If enough ions move through, the voltage change across the membrane reaches a critical level and the membrane is depolarised
The change in voltage triggers the opening of voltage-gated channels resulting in a wave of depolarisation
Resting potential has to be reset for the next nerve impulse to take place.
When the voltage reaches a critically high level, the voltage-gated Na+ channel closes and the voltage gated K+ channels open.
K+ ions diffuse out of the neuron which restores the resting potential.
Once the resting potential is reached, the K + channel closes again.
107
What allows restoration of the resting membrane potential allow?
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.
108
Following repolarisation the sodium and potassium ion gradients are?
reduced
109
How are ion gradient re-established and resting potential brought back in neurons
The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels by actively transporting excess ions in and out of a cell.
110
What does depolarisation of a patch of membrane cause?
Depolarisation of a patch of membrane causes neighbouring regions of the membrane to depolarise and go through the same cycle, as adjacent voltage-gated sodium channels are opened.
111
When the action potential reaches the end of a neuron what does this cause?
When the action potential reaches the end of the neuron it causes vesicles containing neurotransmitter to fuse with the membrane
This releases neurotransmitter, which stimulates a response in a connecting cell.
112
What are photoreceptor proteins?
Photoreceptor proteins are light sensitive which means that they can sense and respond to light.
113
What does the retina do in the eye?
detect light
114
What are the two types of photoreceptor cells?
RODS
| CONES
115
In animals, the light-sensitive molecule retinal is combined with WHAT membrane protein to form the photoreceptors of the eye.
opsin
116
What type of light do rod cells function in?
Dim light
117
Do rod cells allow colour vision?
No
118
What do rod cells contain
They contain the retinal-opsin complex called rhodopsin.
119
What does rhodopsin absorb to change conformation to become photoexcited rhodopsin?
A photon of light
120
Describe how rods work.
1) A photon of light is absorbed by rhodopsin and changes conformation to photoexcited rhodopsin.
2) Photoexcited rhodopsin activates hundreds of transducin, a G-protein.
3) Each transducin activates one molecule of PDE.
4) PDE breaks down cGMP and reduces its concentration. This results in closure of Na+ channels so the membrane potential increases; this hyperpolarisation stimulates a nerve impulse
121
How many transducin molecules are activated by single photoexcited rhodopsin?
Hundreds
122
Each activated G-protein activates how many molecules of the enzyme phosphodiesterase (PDE).
One
123
PDE cataylses the hydrolysis of a molecule called what?
cyclic GMP (cGMP). Each active PDE breaks down thousands of cGMP molecules per second.
124
The reduction in cGMP concentration as a result of its hydrolysis affects the function of what?
ion channels in the membrane of rod cells.
125
The reduction in cGMP concentration as a result of its hydrolysis affects the function of ion channels in the membrane of rod cells. What does this result in?
This results in the closure of ion channels in the membrane of the rod cells.
The inward leakage of positive ions is halted so the membrane potential increases. This triggers a nerve impulse in neurons in the retina.
126
why can rod cells being 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.
127
Describe cone cells?
In cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths (red, green, blue or UV).
128
Do cone cells allow colour vision and only function in bright light.
Yes
129
Why do eukaryotic cells have a cytoskeleton?
Gives the cell its shape, provides mechanical support and helps to maintain organisation within the cell.
130
Why is the cytoskeleton crucial?
It is crucial for cell division to occur or for movement to take place.
131
What does the cytoskeleton consist of?
The cytoskeleton consists of different protein structures including microtubules
132
What are microtubules and what are they composed of?
Microtubules are hollow cylinders composed of the protein tubulin.
133
Where do microtubules radiate from?
They radiate from the microtubule organising centre (MTOC) or centrosome.
134
What do microtubules control?
These microtubules control the location and movement of membrane-bound organelles and chromosomes
135
Cell division requires remodelling of the what?
cytoskeleton.
136
Formation and breakdown of microtubules involves
| what?
polymerisation (growth of the microtubule) and depolymerisation (shrinkage of the microtubule) of tubulin
137
Microtubules form what for cell division?
Spindle fibres
138
Cell division allows organisms to do what?
grow and develop to replace dead cells and repair tissue.
139
What are the two major phases in the cell cycle of a eukaryotic cell?
Interphase: a period of cell growth and DNA synthesis.
Mitotic phase: two identical daughter cells formed.
140
The interphase is divided into three parts, name and describe these parts
1. G1: The initial growth phase. Protein synthesis occurs and new organelles are formed.
2. Synthesis (S): Replication of nuclear DNA.
3. G2: Second phase of growth prior to mitosis.
141
What are the two processes of the mitotic phase?
Mitosis: the chromosomal material is separated by the spindle fibres
Cytokinesis: The cytoplasm is separated into two daughter cells.
142
Mitosis can be divided into four stages what are these 4 stages?
Prophase
Metaphase
Anaphase
Telophase
143
What happens during prophase?
DNA condenses in chromosomes which now consist of two sister chromatids.
The nuclear membrane breaks down
Microtubules extend from the MTOC by polymerisation and attach to the chromosomes via their kinetochores in the centromere region.
144
What are kenetichores?
a point where the spindle fibres binds
145
What happens during the metaphase?
Chromosomes are aligned at the metaphase plate (the equator of the spindle).
146
What happens during the anaphase?
separation of sister chromatids.
The chromatids are pulled apart as spindle microtubules shorten by depolymerisation.
Chromosomes are pulled to opposite poles
147
What happens during the telephase?
Chromosomes decondense and the nuclear membranes are formed around each set of chromosomes.
148
What happens during the cytokinesis?
After mitosis, cytokinesis occurs.
This involves the separation of the cytoplasm into 2 daughter cells.
149
Why is timing essential in the cell cycle?
Timing is essential because:
Different cell types need to replicate at different times and in different quantities.
Each event within the cell cycle must be complete before the start of the next event.
150
Progression through the cell cycle is controlled by checkpoints at what?
G1,G2, and metaphase
151
What are the checkpoints?
Checkpoints are 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.
152
What are the cyclin proteins involved in?
regulating cell cycle
153
Cyclins combine with and activate what?
cyclin-dependent kinases (CDKs)
154
What do active cyclin-CDK complexes phosphorylate?
proteins that regulate progression through the cycle.
155
If sufficient phosphorylation occurs progression occurs. If insufficient phosphorylation occurs then the cell cycle is what?
Halted
156
What does the RetinoBlastsoma protein act as?
Retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication. It does this by binding to the transcription factor. The transcription factor can no longer stimulate gene transcription.
157
What happens at the G1 checkpoint?
As cyclins accumulate and bind to CDKs during G1, Rb is phosphorylated and becomes inhibited. Phosphorylated Rb changes shape and can no longer bind to the transcription factor.
This allows transcription of the genes that code for proteins needed DNA replication.
Cells progress from G1 to S phase.
158
What happens at the G2 checkpoint?
By the end of G2 DNA replication has occurred.
At the G2 checkpoint, the success of DNA replication and any damage to DNA is assessed.
159
What is triggered if DNA damage has occurred and what can it stimulate?
P53
DNA repair
arrest of cell cycle
cause cell death
160
What happens at the metaphase checkpoint?
The metaphase checkpoint controls progression from metaphase to anaphase
At the metaphase checkpoint, progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.
This ensures each daughter cell receives the correct number of chromosomes.
161
An uncontrolled reduction in the rate of the cell cycle may result in WHAT?
degenerative disease
162
An uncontrolled increase in the rate of the cell cycle may result in WHAT?
tumour formation
163
What is a proto-oncogene and what can it mutate into?
proto-oncogene is a normal gene, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene
164
What is apoptosis?
programmed cell death
165
Why is apoptosis important?
Apoptosis is essential during development of an organism to remove cells no longer required as development progresses or during metamorphosis.
Our hands are not webbed due to apoptotic process during our development.
166
Why may cells initiate apoptosis?
Absence of growth factors
167
How is apoptosis triggered?
Apoptosis is trigged by cell death signals that can be external or internal.
168
Describe external signals triggering apoptosis?
External signals = death signal molecules from lymphocytes
External death signals bind to a surface receptor protein and trigger a protein cascade within the cytoplasm
169
Describe internal signals triggering apoptosis?
Internal signals = DNA damage
An internal death signal resulting from DNA damage causes activation of p53.
170
What happens during apoptosis
Both types of death signal result in the activation of caspases (types of protease enzyme) that cause the destruction of the cell by triggering the degradation of any protein molecule.
