2.3 and 2.4 Flashcards
Describe the fluid mosaic model of membrane structure:
Molecules free to move laterally in phospholipid bilayer
Many components- phospholipids, proteins, glycoproteins and glycolipids
Describe the arrangement of the components of a cell membrane:
Phospholipids form a bilayer
Proteins
- intrinsic span bilayer
- extrinsic on surface of membrane
Glycolipids found on exterior surface
Glycoproteins found on exterior surface
Cholesterol bonds to phospholipid hydrophobic fatty acid tails
Explain the arrangement of phospholipids in a cell membrane:
Bilayer with water present on either side
Hydrophobic fatty acid tails repelled from water so point away from water
Hydrophilic phosphate heads attracted to water so point to water
Explain the role of cholesterol in cell membranes:
Restricts movement of other molecules making up membrane
So decreases fluidity/increases rigidity
Suggest how cell membranes are adapted for other functions:
Phospholipid bilayer is fluid- membrane can bend for vesicle formation/phagocytosis
Glycoproteins/glycolipids act as receptors/antigens involved in cell signalling/recognition
Describe how movement across membranes occurs by simple diffusion:
Lipid soluble or very small substances move from an area of higher conc to an area of lower conc down a conc gradient
Across phospholipid bilayer
Passive- doesn’t require energy from ATP/respiration
Explain the limitations imposed by the nature of the phospholipid bilayer:
restricts movement of water soluble (polar) and larger substances
Due to hydrophobic fatty acid tails in interior of bilayer
Describe how movement across membranes occurs by facilitated diffusion:
Water soluble (polar) / slightly larger substances
Move down conc. gradient
Through specific channel/carrier proteins
Passive- doesnt require energy from ATP/respiration
Explain the role of carrier/channel proteins in facilitated diffusion:
Shape/charge of protein determines which substances move
Channel proteins facilitate diffusion of water soluble substances
- hydrophilic pore filled with water
- may be gated
Carrier proteins facilitate diffusion of slightly larger substances
- complementary substances attaches to binding site
- protein changes shape to transport substance
Describe how movement across membranes occurs by osmosis
Water diffues/moves
From an area of high to low water potential/ down water potential gradient
Through a partially permeable membrane
Passive- doesn’t require ATP/respiration
Describe how movement occurs by active transport:
Substances move from an area of lower to higher conc/against conc. gradient
Requiring hydrolysis of ATP and specific carrier proteins
Describe the role of carrier proteins and the importance of hydrolysis of ATP in active transport:
Complementary substance binds to specific carrier proteins
ATP binds, hydrolysed into ADP + Pi releasing energy
Carrier protein changes shape, releasing substance on side of higher concentration
Pi released- protein returns to original shape
Describe how movement across membrane occurs by co-transport:
Two different substances bind to and move simultaneously via a co-transporter protein
Movement of one substance against its concentration gradient is often coupled with the movement of another down its concentration gradient
Describe the co transport of glucose:q
Na+ actively transported from epithelial cells to blood
Establishes a conc. gradient of Na+
Na+ enters epithelial cell down its conc. gradient with glucose against its conc. gradient
Via a co-transporter protein
Glucose moves down a conc. gradient into blood via facilitated diffusion
What increases the rate of movement across membranes?
Increasing SA, number of channel/carrier proteins, conc. gradient, water potential
Explain the adaptations of specialised cells in relation to the rate of transport across their internal and external membranes:
Membrane folded (e.g microvilli) to increase SA
More protein channels/carriers for facilitated diffusion
Large number of mitochondria to make more ATP by aerobic respiration for active transport
What is an antigen?
Foreign molecule/protein
that stimulates an immune response leading to production of antibody
How are cells identified by the immune system?
Each type of cell has specific molecules on its surface that identify it
Often proteins with a specific tertiary structure
What type of cells and molecules can the immune system identify?
Pathogens
Cells from other organisms of the same species
Abnormal body cells
Toxins
Describe phagocytosis:
Phagocyte attracted by chemicals/recognises antigens on pathogen
Phagocyte engulfs pathogen by surrounding it with its cell membrane
Pathogen contained in vesicle/phagosome in cytoplasm of phagocyte
Lysosome fuses with phagosome and releases lysozymes
Lysozymes hydrolyse pathogen
Antigens presented on cell surface membrane of phagocyte (APC) stimulating the specific immune response
Describe the response of T lymphocytes to a foreign antigen (cellular response):
Specific helper T cells with complementary receptors on cell surface bind to antigen on antigen presenting cell
Activated and divide by mitosis to form clones which stimulate:
- cytotoxic T cells which kill infected/tumour cells
- specific B cells
- phagocytes- engulf pathogens by phagocytosis
Describe the response of B lymphocytes to a foreign antigen (humoral response)
- Clonal selection
- specific B lymphocytes with complementary receptor binds to antigen
- then stimulated by helper T cells
- so divides rapidly by mitosis to form clones - Some differentiate into B plasma cells which secrete large amounts of monoclonal antibody
- Some differentiate into B memory cells which remain in blood for secondary immune response
What are antibodies?
Quaternary structure proteins
Secreted by B lymphocytes in response to specific antigens
Bind specifically to antigens forming antigen antibody complexes
Explain how antibodies lead to destruction of pathogens:
Antibodies bind to antigens on pathogens forming an antigen-antibody complex
- specific tertiary structure so binding site/variable region binds to complementary antigen
Each antibody binds to 2 pathogens at a time causing agglutination of pathogens
Antibodies attract phagocytes
Phagocytes bind to the antibodies and phagocytose many pathogens at once
Explain the difference between primary and secondary immune response
Primary=first exposure to antigen
- antibodies produced slowly and at a lower conc.
- takes time for specific B plasma cells to be stimulated to produce specific antibodies
- memory cells produced
Secondary=second exposure to antigen
- antibodies produced faster and at a higher conc.
- B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies
What is a vaccine?
Injection of antigens from attenuated pathogens
Stimulating formation of memory cellls
Explain how vaccines provide protection to individuals against disease:
Specific B lymphocyte with complementary receptors binds to antigen
Specific T helper cells bind to antigen presenting cell and stimulates B cell
B lymphocytes divide by mitosis to form clones
Some differentiate into B plasma cells which release antibodies
Some differentiate into memory B cells
On secondary exposure to antigen, B memory cells rapidly divide by mitosis to produce B plasma cells
These release antibodies faster and at a higher conc.
Explain how vaccines provide protections for populations against disease:
Herd immunity so large proportion of population vaccinated, reducing spread of pathogen
- large proportion of population immune so do not become ill from infection
- fewer infected people to pass pathogen on/unvaccinated people less likely to come in contact with someone with disease
Describe the difference between active and passive immunity:
Active:
Initial exposure to antigen (e.g vaccine or infection), memory cells involved, antibody produced and secreted by B plasma cells, slow as takes longer to develop, long term immunity as antibody can be produced in response to a specific antigen again
Passive:
No exposure to antigen and no memory cells involved. Antibody introduced from another organism (e.g breastmilk) faster acting but short term immunity as antibody hydrolysed
Explain the effect of antigen variability on disease and disease prevention:
Antigens on pathogen change shape/tertiary structure due to gene mutations
SO no longer immune
- B memory cell receptors cannot bind to/recognise changed antigen on secondary exposure
- specific antibodies not complementary/cannot bind to changed antigen
Describe the structure of a HIV particle:
Lipid envelope, RNA, reverse transcriptase, capsid, attachment protein
Describe the replication of HIV in helper T cells:
- HIV attachment proteins attach to receptors on helper T cells
- Lipid envelope fuses with cell surface membrane, releasing capsid into cell
- Capsid uncoats, releasing RNA and reverse transcriptase
- Reverse transcriptase converts viral RNA to DNA
- Viral DNA inserted/incorporated into helper T cell DNA
- Viral protein/capsid/enzymes are produced
- DNA transcribed into HIV mRNA
- HIV mRNA translated into new HIV proteins - Virus particles assembled and released from cell
Explain how HIV causes the symptoms of AIDS:
HIV infects and kills helper T cells as it multiplies rapidly
- So helper T cells can’t stimulate cytotoxic T cells, B cells and phagocytes
- So B plasma cells can’t release as many antibodies for agglutination and destruction of pathogens
Immune system deteriorates- more susceptible to infections
Pathogens reproduce, release toxins and damage cells
Explain why antibiotics are ineffective against viruses:
Viruses do not have metabolic processes/ribosomes
Viruses do not have bacterial enzymes/murein cell wall
What is a monoclonal antibody?
Antibody produced from genetically identical/cloned B lymphocytes/plasma cells
So have same tertiary structure
Explain how monoclonal antibodies can be used in medical treatments:
Monoclonal antibody has a specific tertiary structure/binding site/variable region
Complementary to receptor/protein/antigen found only on a specific cell type
Therapeutic drug attached to antibody
Antibody binds to specific cell, forming antigen-antibody complex, delivering drug
Explain how monoclonal antibodies can be used in medical diagnosis:
Monoclonal antibody has a specific tertiary structure/binding site/variable region
Complementary to receptor/protein/antigen associated with diagnosis
Dye/stain/fluorescent marker attached to antibody
Antibody binds to receptor/protein/antigen, forming antigen-antibody complex
Explain the use of antibodies in the ELISA test to detect antigens:
DIRECT:
Attach sample with potential antigens to well
Add complementary monoclonal antibodies with enzymes attached- bind to antigens if present
Wash well- remove unbound antibodies
Add substrate- enzymes create products that cause a colour change
INDIRECT:
Attach specific monoclonal antibodies to well
Add sample with potential antigens then wash well
Add complementary monoclonal antibodies with enzymes attached- bind to antigens if present
Wash well- remove unbound antibodies
Add substrate- enzymes create products that cause a colour change
Suggest the purpose of a control well in the ELISA test:
Compare to test to show only enzyme causes colour change
Compare to test to show all unbound antibodies have been washed away
What are the ethical issues of vaccines and monoclonal antibodies?
Pre-clinical testing on/use of animals- potential stress/harm/mistreatment
-But animals not killed and helps produce new drugs to reduce human suffering
Clinical trials on humans- potential harm/side effects
Vaccines- people may continue high risk activities and still develop/pass on pathogen
Use of drug- potentially dangerous side effects
