Module 1 - What is a Cell? Flashcards
1
Q
Define physiology
A
= study of the functions of living things
2
Q
Define anatomy
A
= study of the structure of the body
3
Q
List and describe the elements of physiology
A
- Atoms and Molecules= various atoms and molecules that make up the body. The atom is the smallest building block of matter
e. g. a molecule in the membrane that encloses a cell - Cells = cells are the basic units of life
e. g. a cell in the stomach lining - Tissues = tissues are groups of cells of similar specialisation
e. g. layers of tissue in the stomach wall - Organs = an organ is a unit made up of several tissues
e. g. the stomach - Body systems = a collection of related organs
e. g. the digestive system - Whole organism
e. g. the whole person
4
Q
Describe Extracellular Fluid (ECF)
A
- internal to body; external to cell
- 2 types:
i. interstitial fluid (between cells)
ii. blood plasma
5
Q
Describe Intracellular Fluid (ICF)
A
- fluid inside cell
6
Q
Describe homeostasis
A
- the maintenance of relatively stable conditions inside the body (despite large changes to the external environment)
- homeostasis is a dynamic steady state (small changes occur within narrow limits)
7
Q
Describe regulating homeostasis
A
- homeostasis is controlled by nervous and endocrine systems
- the body responds to internal changes through homeostatic control systems
> negative feedback loop
> positive feedback loop
8
Q
Describe a negative feedback loop
A
- maintains homeostasis -> very common
- a change in the body is detected
- mechanisms are set in place to bring the variable back to normal
i.e.
if changed factor is higher, the body will aim to lower to the homeostatic range (and vice versa)
- aiming to bring variable back to homeostatic range
9
Q
Give an example of a negative feedback loop
A
- fall in body temp below set point
- temp monitoring nerve cells
- temp control centre
- skeletal muscle (and other effectors)
- increase heat production through shivering
- Increase in body temp to set point
- relieves low body temp
10
Q
Describe a positive feedback loop
A
- allows the body to operate outside the homeostatic range
- occurs when a physiological change leads to an even greater change (amplification effect)
- less common than negative feedback
11
Q
Give an example of a positive feedback loop
A
- Head of fetus pushes against cervix
- Nerve impulses from cervix transmitted to brain
- brain stimulates pituitary gland to secrete oxytocin
- oxytocin stimulates uterine contractions and pushes fetus towards cervix
12
Q
List the 3 basic components of a cell
A
- nucleus
- cytoplasm
- plasma membrane
13
Q
Describe the nucleus
A
- control centre for the cell
- controls protein synthesis
- contains DNA
- genetic material
- blueprint for the activity of all cells
- surrounded by the nuclear envelope (membrane around nucleus)
- nuclear pores allow movement of molecules into and out of nucleus
14
Q
Describe the process of DNA to RNA to Protein
A
- DNA =deoxyribonucleic acid = genetic code
- mRNA = messenger ribonucleic acid
- produced from DNA blueprint
- directs the productions proteins
- proteins = carry out biological functions
15
Q
List the steps of DNA-RNA-protein
A
- synthesis of mRNA in nucleus (from DNA)
- Movement of mRNA into cytoplasm via nuclear pore
- synthesis of protein
16
Q
Describe ribosomes
A
- needed for protein synthesis
- ribosomes are responsible for reading mRNA and make the protein
17
Q
Describe Free ribosomes
A
- suspended in cytosol (solution inside cell; ICF)
- proteins that function in the cytosol
18
Q
Describe Bound ribosomes
A
- bound to endoplasmic reticulum
- proteins that function in membrane; within an organelle; outside of the cell
19
Q
Describe cytoplasm
A
consists of:
- organelles
- cellular organs
- most surrounded by a membrane
- cytosol
- jelly-like fluid
- cytoskeleton
- skeleton of the cell
- maintains shape and allows movement
20
Q
describe the endoplasmic reticulum (ER)
A
- extensive network of membrane joining the nucleus
- 2 types
i. rough ER
ii. smooth ER
21
Q
Describe rough ER
A
- covered in ‘rough’ ribosomes
- proteins are made at the rough ER
- acts as a ‘membrane factory’
22
Q
Describe smooth ER
A
- packages protein from rough ER
- packages and transports proteins to the Golgi complex in transport vesicles
- has specialised functions in particular cells
e. g. - detoxification (liver, kidneys)
- making steroid-based hormones (testes)
- releasing calcium for muscle contraction (skeletal and cardiac muscle)
23
Q
Describe Golgi complex
A
- series of curved sacs
- Golgi complex accepts transport vesicles from the ER for further processing
- role = proteins are modified and ‘shipped’ to their final destination
- outside the cell
- to various membranes
- to the organelles
24
Q
describe lysosomes and peroxisomes
A
= recycling/garbage facility of the cell
- membrane bound vesicles containing enzymes (molecules that speed up chemical reactions without getting consumed by the reaction)
- bud off the Golgi complex
- lysosome = break down organic material inside the cell
- peroxisomes= degrade toxic molecules inside the cell
25
Describe the mitochondria
- the power plant of the cell
- converts food energy into cellular energy
ATP = adenosine triphosphate
26
Describe ATP
- the chemical bond between the last 2 phosphate groups is broken
- energy is released when terminal phosphate group is removed
- how do we use ATP
1. synthesis of new compounds (e.g. proteins)
2. transport of molecules across membrane
3. mechanical work (contraction of muscle cells)
27
Describe the 4 main functions of plasma membrane
1. forms a mechanical barrier = separate ICF from ECF
2. selective permeability = determines which molecules can move between the ICF and ECF
3. electrochemical gradient = important for neural and muscle function
4. communication and cell signalling= receiving and interpreting messages from other cells
28
Describe the 7 step process of protein synthesis
1. the rough ER synthesises proteins to be secreted to the exterior or to be incorporated into plasma membrane or other cell compartments
2. the smooth ER packages the secretory product into transport vesicles, which bud off and move to the Golgi complex
3. the transport vesicles fuse with their Golgi complex, open up, and empty their contents into the closest Golgi sac
4. the newly synthesised proteins from the ER travel by vesicular transport through the layers of the Golgi complex which modifies the raw proteins into final form and sorts and directs the finished products to their final destination by varying their wrappers
5. secretory vesicles Fontaine the finished protein products bud off the Golgi complex and remain in the cytosol, soaring the products until signalled to empty
6. on appropriate stimulation, the secretory vesicles fuse with the plasma membrane open and empty their contents to the cells exterior. Secretion has occurred by exocytosis, with the secretory products never having come into contact with the cytosol
7. lysosomes also bud from the Golgi complex
29
Describe the plasma membrane
- the plasma membrane is a lipid bilayer
- 2 layers of phospholipids
- phospholipids have a 'head' and two 'tails'
* phosphate head is hydrophilic
* fatty-acid tails are hydrophobic
30
describe phospholipids
- ECF and ICF are mainly made up of water
- phospholipid bilayer organises itself in a way that the hydrophilic head orientates themselves towards the water and the lipophilic tails orientated themselves towards the centre of the cell
- this orientation determines what molecules can pass across the membrane
31
Describe membrane protein and their functions
- transport of molecules between the ICF and ECF
- cell communication
- attaching to the EC environment or to other cells
- enzymatic activity
- cell to cell recognition
32
Describe Desmosomes (cell junctions)
- joints 2 cells together without touching
- bound by glycoprotein filaments attached to thickened cytoplasm
- prevents tearing of the tissue when stretched
e. g. epidermis cells, cardiac cells
33
Describe tight junctions (cell junctions)
- membrane proteins from adjacent cells fuse together
- prevents passage of molecules between adjoining cells
e. g. nephrons in kidney, intestine cells
34
Describe gap junctions (cell junctions)
- tunnels from one cell to another
- transport of ions and small molecules between cells
e. g. some nervous system cells, cardiac cells
35
Describe transport across the plasma membrane
- the plasma membrane is selectively permeable (only some molecules can pass freely across the membrane)
- passage across the membrane is dependent on 2 things:
1. particle size
2. lipid solubility of particle
36
List molecules that are permeable to the plasma membrane and why
- gases (oxygen and carbon dioxide) = small and uncharged; hydrophobic
- water and ethanol = polar (hydrophilic) but small
37
List molecules that are impermeable to the plasma membrane and why
- ions = small but charged (hydrophilic)
| - glucose and proteins= large and polar/charged (hydrophilic)
38
Describe Passive Transport
- doesn't require energy (ATP)
- simple diffusion
- osmosis
- facilitated diffusion (channels and carriers)
39
Describe Active Transport
- requires energy (ATP)
- primary active transport
- secondary active transport
- vesicular transport (endocytosis and exocytosis)
40
Define diffusion
= the movement of molecules from an area of high concentration to an area of low concentration
41
What is diffusion due to?
- molecules are in constant random motion
| - collisions cause the molecules to spread out
42
Describe concentration gradients
gradient= difference between 2 places
- differences in concentration across 2 areas is called a concentration gradient
- the greater the difference between the two areas, the greater the concentration gradient
43
Describe diffusion in relation to concentration gradients
- molecules diffuse down the concentration gradient
- the molecules will eventually reach an equilibrium (evenly distributed)
- gradients can also be formed by electrically charged particles (electrical gradient, opposite charges attract; same charge repels)
- combined force of concentration and charge (electrochemical gradient)
44
List and describe the 5 contributors to Diffusion rate
1. The size of the concentration gradient
bigger gradient = faster diffusion
2. Membrane surface area
bigger surface area = faster diffusion
3. Size of the molecule
small molecules diffuse more quickly than large molecules
4. Diffusion distance
decreasing diffusion distance= increasing diffusion rate
5. Lipid solubility of the molecule
whether the molecule can pass through the lipid part of the membrane
45
Describe Hydrophobic/lipophilic
= enters membrane easily
- fatty acid
- steroid hormones
46
Describe Hydrophilic/lipophobic
= repelled by membrane
- most substances in the body
- very few substances pass into cells by simple diffusion
47
Define solution
= combination of solute and solvent
48
Define Solvent
- liquid that substances dissolve into
| - usually water in biology
49
Define solute
= substances that dissolve in liquids
50
Define penetrating solutes
= can cross the plasma membrane
51
Define non-penetrating solutes
= cannot cross the membrane
52
Define osmosis
- the diffusion of water across a selectively permeable membrane
Use either of the 2 definitions:
1. the movement of water from an area of high water concentration to an area of low water concentration
2. the movement of water from an area of low solute concentration to an area of high solute concentration
53
Describe the resultant if the membrane is permeable to solutes and water
= if the membrane that separates the solutions is permeable to both water and solutes, then both can move until they reach an equilibrium
54
Describe the resultant if the membrane is impermeable to solutes and permeable to water
= if the membrane that separates the solutions if permeable to water, but impermeable to solutes, the water will diffuse across the membrane (osmosis), but the solutes won't = unbalanced
55
Define osmolarity and give the unit
osmolarity = number of solute particles per litre of solution
unit:
milliosmoles/litre
mOsm/L
56
What is the osmolarity of most body fluids ?
300 mOsm/L
57
Define tonicity
- the ability of a solution to change the shape (tone) of a cell by changing the cells internal water volume (via osmosis)
- depends on the concentration of non-penetrating solutes on either side of the cell membrane
58
Describe isotonic
= same concentration of non-penetrating solutes as ICF
| - results in no cell change
59
Describe hypertonic
= higher concentration of non-penetrating solutes than ICF
| - results in cell shrivelling/shrinking
60
Describe hypotonic
= lower concentration of non-penetrating solutes than ICF
| - results in cell bursting/swelling
61
Describe transport proteins
= molecules that can't diffuse across the plasma membrane can travel through transport proteins
- span the plasma membrane
- channel and carrier proteins
62
Describe facilitated diffusion
- down the concentration gradient
- does not require ATP
- uses channel or carrier protein
63
Describe CHANNELS (facilitated diffusion)
- hydrophilic tunnel through the plasma membrane
- transports small molecules (i.e. ions)
- some channels are gated (open or close in response to a stimulus)
64
Describe the 4 step process of CARRIERS (facilitated diffusion)
1. Carrier protein takes conformation in which solute binding site is exposed to region of higher concentration
2. Solute molecule binds to carrier protein
3. Carrier protein changes conformation so that binding site is exposed to region of lower concentration
4. Transported solute is released and carrier protein returns to original conformation
65
List some characteristics of channels
- transport for small ions and water (aquaporins)
- can be open or closed
- open to both sides of the membrane simultaneously
- allows rapid transport of molecules
66
List some characteristics of carriers
- transport for larger hydrophilic molecules (glucose and amino acids)
- are always open
- only open to one side of membrane
- slower movement of molecules
67
Describe Active transport
- transport through a carrier against the concentration gradient
- requires ATP
- primary active transport (directly uses ATP)
- secondary active transport (indirectly uses ATP)
68
Describe primary active transport
- the terminal phosphate group in ATP is transferred to the carrier
*called phosphorylation
*causes the carrier to change shape
example= sodium-potassium pump
69
Describe the 6 step process of primary active transport; Na+/K+ ATPase
1. Pump has 3 high-affinity sites for Na+ and 2 low-affinity sites for K+ when exposed to ICF
2. When 3 Na+ from ICF (where Na+ concentration is low) bind to pump, it splits ATP into ADP plus phosphate; phosphate group binds to pump
3. Phosphorylation causes pump to change conformation so that Na+ binding sites are exposed to opposite side of membrane and 3 Na+ are released to ECF (where Na+ concentration is high) as affinity of Na+ binding sites greatly decreases
4. Change in shape also exposes pumps binding sites for K+ to ECF and greatly increases affinity of K+ sites
5. When 2 K+ from ECF (where K+ concentration is low) bind to pump, it releases phosphate group. Dephosphorylation causes pump to revert to its original conformation
6. Two K+ are released into ICF (where K+ concentration is high) as affinity of K+ binding sites markedly decreases during change in shape. At the same time, affinity of Na+ binding sites greatly increases, returning process to Step 1
70
Describe Secondary active transport
- the movement of a solute down its concentration gradient provides a 'driving force' energy for the movement of a second solute against the concentration gradient
- two solutes transported together in the same (symport) or opposite (anti port) direction
71
Describe the 3 step process of Secondary Active Transport; using example of Sodium-Glucose Transport Proteins (SGLT)
1. Binding of Na+ on luminal side, where Na+ concentration is higher, increased affinity of SGLT for glucose. Therefore, glucose also binds to SGLT on luminal side where glucose concentration is lower
2. When both Na+ and glucose are bound, SGLT changes shape, opening to cell interior
3. SGLT releases Na+ to cell interior, where Na+ concentration is lower. Because affinity of SGLT for glucose decreases on release of Na+, SGLT also release glucose to cell interior, where glucose concentration is higher
72
Describe the complex 3 step example of Intestinal cells
Step 1: Primary active transport
= Na+ is pumped out of the cell to reduce the concentration within the cell
Step 2: Secondary active transport
= glucose is pumped against its concentration gradient as sodium rushes in along its concentration gradient
Step 3: Facilitated diffusion through a carrier
= glucose can travel down its concentration gradient to get into bloodstream
73
Describe Vesicular transport
- transfer of materials between ECF and ICF within vesicles (fluid-filled sacks enclosed by membrane)
- requires energy from ATP
74
Describe the 2 types of vesicular transport
1. Endocytosis= vesicular transport into the cell
| 2. Exocytosis= vesicular transport out of the cell
75
Describe the 3 types of Endocytosis
1. Receptor Mediated endocytosis
= uptake triggered when target molecule binds to receptors on the plasma membrane
2. Pinocytosis (cell drinking)
= uptake of ECF
3. Phagocytosis (cell eating)
= uptake of solid objects such as bacteria and cellular debris
76
Describe the 7 step process of Receptor Mediated Endocytosis
1. Target molecules (ligands) bind to receptors in plasma membrane
2. Areas coated with ligands form deep pockets in plasma membrane surface
3. Pockets pinch off, forming endosomes known as coated vesicles
4. Coated vesicles fuse with primary lysosomes to form secondary lysosomes
5. Ligands are removed and absorbed into the cytoplasm
6. The lysosomal and endosomal membranes separate
7. The endosome fuses with the plasma membrane, and the receptors are again available for ligand binding
77
Describe the 3 step process of Pinocytosis
1. Solute molecules and water molecules are outside the plasma membrane
2. Membrane pockets inward, enclosing solute molecules and water molecules
3. Pocket pinches off as endocytic vesicle containing sample of ECF
78
Give some more info about Pinocytosis
- non-selective uptake of fluid (water, ions, glucose)
| - a way to recover 'extra' plasma membrane added to the cell surface during exocytosis
79
Describe the 5 step process of Phagocytosis
1. The phagocytic white blood cell encounters a bacterium that binds to the cell membrane
2. The phagocyte uses its cytoskeleton to push its cell membrane around the bacterium, creating a large vesicle, the phagosome
3. The phagosome containing the bacterium separates from the cell membrane and moves into the cytoplasm
4. The phagosome fuses with lysosomes containing digestive enzymes
5. The bacterium is killed and digested within the vesicle
80
Describe Exocytosis
= the reverse of endocytosis
- secretory vesicles are released from the Golgi complex. They bind to the cell membrane, releasing their contents
- secretory vesicles may release products continuously (unregulated) or may remain in the cell until release is triggered (regulated)
regulated= release of neurotransmitters from a neuron depends on the presence of calcium
