Topic 6 Flashcards
Explain how scientists estimate time of death
-From TOD, metabolic reactions slow down causing body temperature to fall until it equates to temp of surroundings
-Scientists have determined body temperature to cool at a rate of 2ish degrees an hour however enviroment can affect this rate
-5 Hours after TOD, muscles begin to contract and become stiff (rigor mortis) which begins when muscles lack oxygen - anaerobic respiration occurs which builds up lactic acid
-Lactic acid decreases pH which inhibit enzymes producing ATP
-No ATP leads to bonds between myosin and actin to become fixed which stiffens the body
-A dead body is colonised by many insects, scientists can identify the type of insect present at a time - flies are usually first then beetles
-Analysis of larvae offspring (hatched after 24h, subject to conditions) and where it is in its life cycle allows an inference of TOD
Explain extent of decomposition and stage of succession
-At death, bacteria and enzymes immediantly become decomposing
-Scientists can use extent of decomposition to find a TOD
-This is a table of approx time since death and a description of what occurs at a time after death
-Type of organism found in a dead body changes over time through a number of stages, this is succession in which scientists can identify what time a stage occurs and infer a TOD
-Immediantly after TOD, conditions are favourable for bacteria
-After bacteria decomposes tissue, conditions favour to flies and their larvae
-Larvae feed on a dead body to make it favourable to beetles
-As a body dries out, conditions do not favour flies so they leave
-Beetles stay to decompose the dried tissues
-When no tissue remain, conditions are no longer favourable for most
Explain DNA profiling / PCR
-Fingerprint of an organisms DNA, everyone’s differs unless you are an identical twin
-A sample of DNA is obtained using organism’s DNA profile such as blood or saliva
-Polymerase Chain Reaction is used to make many copies of specific DNA regions
-A reaction mixture is set up containing DNA sample, free nucleotides, primers and DNA polymerase
-DNA is heated to 95deg to break H bonds between strands of DNA
-Cooling occurs to 60deg so primers can bind to strands
-Heating to 75deg to make DNA polymerase work by lining up DNA nucleotides along each template strand - complementary base pairing occurs
-Two new copies have been formed from one cycle of PCR
Explain gel electrophoresis (after PCR)
-Fluorescent tag is added to allow DNA fragments to be viewed under UV light
-Gel electrophoresis is done to seperate DNA
-DNA is placed into a well in a slab of (agarose) gel covered with buffer solution capable of conducting electricity
-A current is passed through. DNA fragments (-ve charge) moves towards anode (+ve) at far end of gel
-Shorter fragments move faster therefore further, DNA is seperated according to length
-Once done, using UV light you are able to view the DNA profile and compare it to other ones to establish similarities, more similarities = more related
Explain uses of DNA profiling
-Identify people in forensic science, suspects of a crime
-Determine genetic relationships, lost children
-Prevent interbreeding of animals and plants, interbreeding lowers gene pool and leads to higher chance of genetic disorders
Explain structure of bacteria
-Fragellum, long hair-like rotating structure allows movement - bacteria can have 0 or more
-Ribosomes which produce proteins from mRNA
-Cell wall made of glycoprotein (murein)
-Plasma membrane, contains folds called mesosomes
-Slime capsule to protect bacterium from immune system attacks
-Plasmids, small loop of DNA which aren’t part of chromosomes, bacteria can have 0
-DNA, long circular freefloating coiled
-Pili, to help stick to other cells or used in gene transfer
-Explain structure of viruses
-Microorganisms, nucleic acids surrounded by protein
-No plasma membrane, no cytoplasm or ribosomes
-Contains a core of nucleic acid that is DNA or RNA
-Some carry proteins inside their capsid e.g reverse transcriptase
-Protein coat named capsid
-Some have envelope outer layer stolen from cell membrane of a previous host
-Attachment protein sticking out of cell which allows virus to attack to a host cell
Explain HIV’s development in an organism
-Spread through bodily fluids into the bloodstream
-Can only reproduce inside of T-Helper cells of infected organism
-HIV does not have enzymes to replicate independently, so it uses host cell’s
-Attachment protein binds to receptor protein on membrane of a t-helper cell
-Capsid is released into cell which uncoats and reveals the genetic material (RNA) into cell’s cytoplasm
-Reverse Transcriptase enzyme is used to create a complementary RNA strand and can then make DNA molecules
-DNA is inserted into the human DNA and host cell enzymes make proteins from the DNA - creating more of HIV, cycle repeats
Explain the barriers to prevent bacteria
-Stomach acid: pathogens may not survive the acidic conditions, if they do they may infect cells of the gut wall and cause disease
-Skin: physical barroer, damage to skin may provide entry to bloodstream
-Gut flora: gut is covered in microorganisms named flora
-Lysozyme: mucosal surfaces (eyes, mouth, nose) secrete lysozymes which kill bacteria by damaging their cell wall
Explain the non specific immune response
-Occurs first at a site of inflammation
-Immune system recognises foreign antigens on C.M of a pathogen and molecules (histamine?) which trigger inflammation is released
-Vasodilation occurs which increases blood flow to site of infection, this also increase permeability of the blood vessels
-This brings many immune system cells to the site which is capable of moving out of blood into the infected tissue to now destroy the pathogen
-When cells are infected, they produce proteins named interferons which help prevent viruses spreading by inhibiting replication
-Interferons also activate cells involved in killing infected cells
-Phagocyte recognise antigens on pathogens, visits it and engulfs it with its cytoplasm, for a lysosome to fuse in and break down the pathogen
-Phagocyte then presents the pathogen’s antigens becoming a antigen presenting cell, to activate other immune system cells
Explain the specific immune response
-Involves WBCS: T and B cells, which produce specific responses against pathogens
-T cell has a surface covered with differing receptor shapes which bind to antigens of APCs such as macrophage/phagocyte
-When a receptor meets a complementary antigen, it binds - each T-Cell carries differing antigens which activates the cell which divides to produce clones of itself
-T helper cells: release substances which activate B, T-Killer cells and macrophages
-T Killer cells: attach to antigens on an infected cell and kills it
-T Memory cells:
-B cells are covered with antibody proteins, which bind to antigens to form a antib-antig complex, this with substances from T cell activate the B cell causing its division by mitosis into plasma cells (B effector cells) and b memory cells
Explain plasma cells
-Plasma cells make antibodies to a specific antigen
-Are clones of B cells which secrete many antibodies into blood
-Antibodies are made of 4 polypeptide chains, 2 heavy and 2 light which has a variable and constant region
-Variable regions are parts which form antigen binding sites which are complementary - these differ between antibodies
-Hinge region allows flexibility for when binding occurs
-Constant regions allow binding to a receptor on immune system cells e.g phagocyte/macrophage
-Disulfide bridges hold the polypeptide chains together
Explain production of memory cells
-When a pathogen enters the body for 1st time, antigens on its surface activate immune system’s non specific response then the specific response - these 2 make the primary response
-Primary response is slow due to lack of B cells required to bind to antigen which becomes produced over time
-After exposure to an antigen, both T and B cells produce memory cells which remain in the body for a long long time
-T memory cells remember the specific antigen which will now recognise the pathogen when it enters to produce the exact amount of B cells required to overcome the infection
-If the pathogen is back, immune system produces quicker and stronger SECONDARY response
-T memory cells divide into correct T cell to kill the cell with the antigen, B memory cells divide into plasma cells which produce correct antibody to antigen
Explain active/passive immunity
-Active immunity is the achieved when an immune system makes its own antibodies after stimulation by antigen
-Natural is when you are immune after catching a disease
-Artificial is when a vaccine is given with the harmless dose of the antigen
-Passive immunity is achieved when you are given antibodies made by a different organism, so the immune system doesn’t produce its own
-Natural is when a baby is immune due to antibodies from the mother through placenta and breast milk
-Artificial is when you are immune after an injection of antibodies
-Passive immunity is short-term however gives immediate protection
-Active is long-term but takes longer for protection to develop
Explain antibiotics
-Prevents the growth of microorganisms
-Bacteriocidal kills bacteria
-Bacteriostatic prevent bacteria replication
-Work by inhibiting bacterial metabolism such as enzymes used to make bbonds in their cell walls
-Work by inhibiting protein production by binding to bacterial ribosomes to carry out protein synthesis for growth
