Week 2 (cell physiology) Flashcards
What are cells?
The basic structural and functional units of the body.
What are the 3 main parts of a cell?
Plasma membrane
Cytoplasm
Nucleus
Describe the plasma membrane
Flexible outer surface
Separates the internal and external environment.
Selective barrier: maintain internal environment.
Regulates flow of material in and out of the cell.
Role in communication.
Not fully rigid.
Within the cell membrane different molecules are embedded which allow it to communicate with other molecules.
String barrier.
Contains the cell cytoplasm.
Fluid mosaic model: composed of lipids and proteins.
Describe the cytoplasm
Contains the cellular material between the membrane and nucleus.
Made up of two components; cytosol and organelles.
What is cytosol?
Intracellular fluid
Made from water, solutes and suspended particles.
Describe the nucleus
Large organelle
Contains most of the cell’s DNA
Chromosomes (genes, control structure and function)
Name the three components of the lipid bilayer
Phospholipids (75%)
Cholesterol (20%)
Glycolipids (5%)
Describe phospholipids
Amphipathic molecules (polar and non-polar)
Polar = hydrophilic phosphate ‘head’
Non-polar = hydrophobic fatty acid ‘tails’ (x2)
Describe cholesterol
Weakly amphipathic
Polar = OH group
Non-polar = steroid ring and hydrocarbon tail
Describe glycolipids
Polar = carbohydrate group
Non-polar = fatty acid tails
Only face extracellular fluid
Name the two membrane proteins
Integral proteins
Peripheral proteins
Describe integral proteins
Extend into or through the lipid bilayer
Embedded
Transmembrane proteins
Amphipathic
Glycoproteins
Proteins with carbohydrates
Project into extracellular fluid
Oligosaccharides
Describe peripheral proteins
Not as firmly embedded
Attached to polar heads of lipids or integral proteins
Important for communicating and anchoring other cells.
Describe glycocalyx and its function
A sugar coating.
Provides a unique signature of the cell to allow recognition.
Protects the cell from being broken down by other enzymes.
Help them to move around the body fluidly.
What are the functions of plasma membrane?
Barrier: separates inside and outside of cell.
Control: regulates the flow of substances in and out of the cell.
Identification: helps cells recognise other cells
Signalling: intracellular communication
What are ion channels?
Pore in the membrane
Selective transport
Forms a pore through which a specific ion can flow to get across membrane.
Most plasma membranes include specific channels for several common ions.
Ion channels are gated.
What are carriers/transportes?
Selective movement
Polar substance/ion
Transports a specific substance across membrane by undergoing a change in shape.
What are receptors?
Recognise and binds specific molecule.
Ligand.
Recognises specific ligan and alters cells function in some way.
What are enzymes?
Specific reactions
Inside or outside cell
Catalyses reaction inside or outside cell (depending on which direction the active site faces).
What are linkers?
Anchor filaments in one cell
Anchor proteins in adjacent cells
Integral and peripheral proteins
Anchors filaments inside and outside the plasma membrane, providing structural stability and shape for the cell.
May also participate in movement of the cell or link two cells together.
What are cell identity markers?
Tissue formation
Defence
Distinguishes your cells from anyone else’s.
An important class of such markers is the major histocompatibility proteins.
Define concentration gradient
Difference in the concentration in the inside vs outside of a cell
Define electrical gradient
Difference in distribution of positive and negative ions
Inner surface more negatively charged, outer surface more positive.
Membrane potential
What is the electrochemical gradient?
Concentration gradient + electrical gradient
Describe a passive process
Move down the concentration or electrical gradient
Uses its own kinetic energy
Simple diffusion
Describe an active process
Move against the concentration or electrical gradient
Uses cellular energy (e.g., ATP)
E.g., endocytosis or exocytosis
Name the 5 factors affecting the rate of diffusion
Steepness of concentration gradient
Temperature
Mass of substance
Surface area
Diffusion distance
Describe simple diffusion
Movement of molecules from an area of high concentration to an area of low concentration.
Passive process
Substances move freely through the plasma membrane.
Non-polar, hydrophobic molecules (e.g., oxygen, carbon dioxide, fatty acids, steroids, fat soluble vitamins).
Small, uncharged polar molecules (e.g., water, urea)
Describe facilitated diffusion
Substances that are too polar or highly charged.
Involves the use of integral proteins (channel or carrier)
Describe channel proteins
Most membrane channels are ion channels which are gated.
Hydrophilic ions.
Numerous potassium and chloride ions.
Fewer sodium and calcium ions.
Slower than free diffusion as limited by number of channels.
Gated - change shape to allow ion to flow (random and regulated by chemicals/electrical charge)
Describe carrier proteins
Solute binds on one side.
Carrier undergoes change in shape.
Solute is released on the other side.
Equilibrium
Limited by number of carriers.
Describe osmosis
Passive process
Water movement from area of high to area of low water concentration.
Water movement from area of low to area of high solute concentration.
Water moves across membrane by either simple diffusion or by aquaporins.
Water is moving according to the osmotic gradient.
Bi-lateral
Only occurs when the membrane is permeable to water but not certain solutes.
Water is moved to balance water concentration and to reach equilibrium.
Why does the control of osmosis have a clinical significance?
Need to ensure that their is enough water so that the cell doesn’t burst or shrink and so the cell functions correctly.
Production of CSF, aqueous humour, tears, sweat and saliva.
Dysfunction related to cataracts, salivary gland dysfunction, neurodegenerative diseases.
Describe osmotic pressure
Higher solute concentration = higher pressure
Prevents water movement
When does cell shape and volume change?
If placed in solutions with different pressure
What does tonicity of solution mean/result in?
Change volume of cells by changing water content
Describe an isotonic solution
Concentration of cell and solution is the same
What happens if a cell is placed in a hypotonic solution?
Lower concentration of solute than cytosol.
Water enters cells faster than it leave.
Cells swell and rupture = lysis
What happens if a cell is placed in a hypertonic solution?
Higher concentration of solute than cytosol.
Water leaves cells faster than it enters.
Cells shrink = crenation.
Give examples of clinical uses of solutions
I.V. isotonic solution (e.g., isotonic saline)
Hypertonic solutions (e.g., cerebral oedema)
- removes water from interstitial fluid into blood
- kidneys excrete excess water
Hypotonic solutions (e.g., dehydration)
- water moves from blood to interstitial fluid to cells
What is active transport?
The process of moving solutes against their concentration gradient.
From an area of low concentration to an area of high concentration.
Requires energy.
Name the two types of active transport and explain how they get their energy
Primary active transport: hydrolysis of ATP.
Secondary active transport: energy in an ion concentration gradient.
Describe primary active transport
Energy from ATP hydrolysis.
Molecules change the shape of a carrier protein.
Solutes are pumped across the membrane against its concentration gradient.
Example = sodium potassium pump
Explain the sodium-potassium pump
Sodium ions are moved into the extracellular fluid against the sodium gradient.
Potassium ions are moved into the cytosol against the potassium gradient.
Potassium and sodium will try to leak back down their electrochemical gradient.
Describe secondary active transport
Uses the energy stored in a sodium or hydrogen concentration gradient that was established using primary active transport (indirect use of ATP).
There is a steep sodium concentration gradient. The sodium ions leak back in and this stored energy is converted to kinetic energy. The kinetic energy is what moves the substance against their concentration gradient.
Involves the use of antiporters and symporters.
Explain the difference between symporters and antiporters
Symporters move substances in the same direction.
Antiporters move substances in the opposite direction.
What is the clinical relevance of active transport?
- digitalis for heart failure
- slows the sodium-potassium pump
- sodium accumulates in the heart muscle
- sodium and calcium antiporters slow and calcium accumulates
- increases force of muscular contraction
Name the three types of vesicle transport
Endocytosis
Exocytosis
Transcytosis
What is endocytosis?
Movement into a cell (i.e., vesicle from plasma membrane).
There are three types of endocytosis.
Name and explain the three types of endocytosis
Receptor-mediator: highly selective, uses specific ligands and forms vesicles.
Phagocytosis: involves phagocytes destroying old cells, viruses and bacteria.
Bulk-phase endocytosis: involves pinocytosis and takes up extracellular fluid.
What is exocytosis?
Movement out of a cell.
Intracellular vesicles fuse with plasma membrane.
It helps to transport released material from a cell, secretory cells, nerve cells, waste and intracellular secretory vesicles.
What is transcytosis?
Transports molecules across a cell.
Utilises both endocytosis and exocytosis.
Often occurs in the GI tract.
Describe the cytoplasm
Cell contents between the membrane and nucleus. It is made up of cytosol and organelles.
What is cytosol?
Intracellular fluid that makes up 55% of cell volume.
It is 75-90% water with dissolved/suspended particles.
Describe organelles
Organelles have a specialised structure, a characteristic shape and have specific functions in growth, maintenance and reproduction.
What is the cytoskeleton and name the its three components in size order
The cytoskeleton is a protein filament network that is involved in cell shape, organisation and movement.
Components (smallest to largest)
- microfilaments
- intermediate filaments
- microtubules
Describe microfilaments
Smallest component of the cytoskeleton.
Actin and myosin.
Most prevalent at the cell edge.
Provide mechanical and movement support.
Describe intermediate filaments
Thicker than microfilaments
Stabilise position of organelles
Cell to cell attachment
Describe microtubules
Largest cytoskeleton components
Unbranched hollow tubes
Tubulin
Cell shape and organelle movement
Describe ribosomes
Site of protein synthesis
High content of ribonucleic acid
A large and small subunit combine to form a complete functional ribosome.
Attached to the endoplasmic reticulum.
What is the endoplasmic reticulum?
Network of membranes as flattened sacs.
Describe the rough endoplasmic reticulum
Ribosomes embedded
Secretory, membrane and organellar proteins
Glycoproteins and phospholipids
Describe the smooth endoplasmic reticulum
Enzymes
Fatty acids and steroid synthesis
Detoxify drugs
Repeated exposure to drug leads to tolerance
Describe the Golgi complex
3-20 saccules
Modify, sort and package proteins
Entry face - receives and modifies proteins from RER.
Intermediate saccules add carbohydrates or lipids.
Exit face - further modification, sorts and packages for destination.
What are lysosomes?
Digestive and hydrolytic enzymes that digest substances that enter via endocytosis
Describe peroxisomes
Contain oxidases
Amino acids/fatty acids
Toxic substances
Describe mitochondria
ATP generation through respiration
High number in muscles, liver and kidneys
High surface area
Apoptosis
What is cancer?
A group of diseases characterised by uncontrolled or abnormal cell division.
What is a tumour?
Excess tissue that develops.
It can be malignant or binign.
How can cancers grow?
- carcinogenesis: multistep process with several mutations
- malignant tumours rapidly and continuously grow
- angiogenesis can occur
- competes with healthy cells for space and nutrients
- secondary tumours
What are the causes of cancer?
- Carcinogens (environmental, chemical, induced gene mutation)
- Oncogenes
- Oncogenic viruses
- Chronic inflammation
How can cancer be treated?
Surgery
Chemotherapy
Radiation
Immunotherapy
Targeted therapy
Stem cell therapy
Hormone therapy
Why do cells age?
Cell division may be limited
Telomeres
Glucose
Autoimmune response
Free radicals and oxidative damage
What is involved in tissue regeneration?
Parenchymal cells
Stromal fibroblasts
What factors affect tissue repair?
Nutrition (protein and vitamins)
Blood circulation (oxygen, nutrients, antibodies)
Age (thinner epithelial cells and fragile connective tissue)
