Topic 6 Flashcards
allele
Different version of the a gene which codes for a different version of the same gene
genome
all the DNA in a cell (all the genes)
What are introns
non-coding regions
what are exons
coding regions
What is the sequence of repeated bases in introns know as?
short tandem repeats or satellites
What is the same and what is different about STR on different chromosomes
They occur at the same place (same loci) however the number of times they are repeated varies
How do introns help scientists create a unique DNA profile?
they are unlikely to have the same combination of STRs with the same number of repeats within.
How is a DNA profile made?
- A sample of DNA is obtained
- Fragments of different lengths are created through cutting up the DNA
- The fragments are separated and visualised
- Then the profile is compared to another
How is DNA obtained?
- Tissue sample is broken down in a buffer solution
- The small suspended particles inc DNA are separated from the rest of the cell debris
- Protease enzymes are incubated with the suspension to remove proteins
- cold ethanol is added to precipitate out the DNA
- The DNA is then washed in a buffer solution multiple times
How are the fragments of DNA created?
Restriction enzymes are used. They will only cut up DNA at specific base sequences. They cut away the STR from the DNA.
What temperature do the 3 stages of a PCR occur at?
95C, 55C and 70C
What go into a PCR thermal cycler along with the sample of DNA?
DNA polymerase, DNA primers with florescent markers and nucleotides
What happens in the 3 stages of cycle 1 of a PCR?
-DNA separates into two strands -Primers (small pieces of DNA with florescent markers) attach at the start of the STR repeated sequence -DNA polymerase attach. Nucleotides are added, extending the DNA from the primer. The STR repeated sequence and DNA adjacent is replicated.
What happens in each cycle of a PCR?
The process is repeated producing copies that are just the STR sequence fragment.
How are DNA fragments separated?
gel electrophoresis
How do you produce a DNA profile?
-Double stranded DNA + restriction enzymes and the DNA is cut into fragments - Fragments of double stranded DNA are loaded into the wells of agarose gel in a tank -Negatively charged DNA moves towards the positive electrode and the fragments separate into invisible bands. -DNA transferred to a nylon membrane. -Membrane placed in bag with DNA probe . -Probe binds to fragments with a complimentary sequence -If DNA probe is radio active x-ray is used. If florescent, it is viewed using UV light.
How can genetic profiling be used to identify paternity?
Offspring inherit one STR from each parent.
When can body temperature be useful in determining time of death?
during the first 24 hours
what curve does the falling of body temperature follow?
Sigmoid curve
What factors effect post mortem cooling
Body size, body position, clothing, air movement, humidity and temperature of suroundings.
What is the sequence of events during rigor mortis?
1 Muscles become starved of oxygen and oxygen dependant reactions stop 2 Respiration of the cells becomes anaerobic and produces lactic acid 3 pH of cell falls, inhibiting enzymes and thus inhibiting anaerobic respiration 4 ATP needed for muscle contraction is no longer produced so bonds between muscles become fixed 5 proteins can no longer move over one another so the muscles and joins become fixed.
Autolysis
When the body’s own enzymes, from the digestive tract and from lysosomes, break down cells.
What is the first sign of decomposition
putrefaction when the abdomen turns green
why does the body turn greenish after death?
The formation of sulfhaemoglobin in the blood
Why does intense heat slow down decomposition
As the enzymes involved in autolysis become denatured.
What effect does temperature have on decomposition?
Warm temps speed it up and lower temperatures slow down decomposition.
when can forensic entomology not be used?
If temperature conditions of the body haven’t been fairly constant
Succession
As one group of organisms feed on a decomposing body conditions change in such a way that they become attractive to another group of organisms.
What is the role of microorganisms in the decomposition of organic matter and the recycling of carbon?
Microorganisms use the corpse as a food source with energy being released through aerobic and anaerobic respiration. Carbon dioxide is released into the atmosphere by the respiring decomposers.
What are flagellum and what is their role?
Long hair like structure that rotates To make bacterium move.
What are pili and what is their role?
Short hair like structures Pili help bacteria stick together and to other cells
Where is DNA in bacteria?
free floating in the cytoplasm
What are plasmids and what is their role?
Small loops of DNA that aren’t part of the chromosome.
What is a capsule and what is its role?
protects the bacterium from attack by cells of the immune system
What are mesosomes?
folds in the cell membrane
What is the cell wall and what is its role?
supports the cell made of a glycoprotein
What are ribosomes and what is their role?
produce proteins from mRNA
What do bacteria have that viruses do not have?
plasma membrane, cytoplasm and ribosomes
lysis
the bursting of a cell
antigens
Foreign material that invades the body
How does infection of TB occur
when droplets containing the bacteria are inhaled into the lungs
What happens once TB is in the lungs?
Bacteria is taken up by a phagocyte. Bacteria survive and replicate inside phagocytes. The infected phagocytes are sealed off in the lungs in tubercles. When in tubercles the bacteria is dormant and shows no obvious symptoms. The dormant bacteria might later become active and overcome the immune system. Reactivation is more likely in people with a weakened immune system.
What are the initial symptoms of TB?
Fever, general weakness and severe coughing caused by inflammation of the lungs.
What are the two ways TB kills a person?
In the lungs- respiratory failure If it spreads- organ failure
How does HIV replicate?
-HIV surface protein binds to cell receptors. The virus envelope fuses with cell surface membrane. -The virus uses the enzyme reverse transcriptase to turn the HIVs RNA into DNA. -Integrase inserts virus DNA into host DNA. -The cells natural process of protein synthesis and host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA. -The viral proteins are assembled into new viruses which bud from the cell and go to infect other cells.
latency period
when HIV replication drops to a lower level and a person wont experience symptoms.
When does HIV become AIDS?
when the CD4 (T helper cell) count goes below 200
What kills a person with AIDs?
Opportunistic infections
What are the 4 non specific immune system responses?
Lysozyme, inflammation, phagocytosis and antimicrobial proteins
How do lysozymes protect against pathogens?
found in tears they kill bacteria by breaking down their cell walls. Also found in saliva and nasal secretion.
How does inflammation occur?
The damaged white blood cells release special chemicals eg histamine. Causing the arterioles in the area to dilate and increasing the permeability of the capillaries. Plasma fluid, white blood cells and antibodies leak from the blood into the tissue causing oedema.
Phagocytes
white blood cells that engulf antigens. Inc neutrophils and macrophages.
phagocytosis
when phagocytes engulf and destroy antigens.
How do antimicrobial proteins provide a defence against pathogens?
They diffuse into the surrounding cells where it prevents microbes from multiplying. It inhibits microbial protein synthesis.
What are the two main types of lymphocytes?
T cells and B cells
Where are B cells produced?
bone marrow
Where are T cells produced?
thymus
What are immunoglobulins?
antibodies
What bonds hold the peptide chains of a T cell?
Disulphide bonds
Explain what happens in the activation of T helper cells
Bacterium with antigen on surface is engulfed by macrophage. Macrophage presents antigens on its surface and becomes an APC. The APC eventually find the T helper cell with the complimentary CD4 receptor. Clonal expansion occurs and the T helper cell activates and divides into more T memory cells and T helper cells.
Explain what happens in clonal selection
Bacterium binds to B cell with complimentary receptor. The B cell becomes an APC. The activated T helper cell with a complimentary receptor binds to the APC (B cell) and produces cytokines that stimulate the B cell. The B cell divides to give B memory and B effector cells. The B effector cells differentiate into plasma cells. The plasma cells secrete antibodies which bind to the antigens.
Explain what happens once the antibodies are produced by the B cell
Antibodies bind to the bacteria with antigens on the surface and label them. Antibodies bind to the antibody receptors on a macrophage. The macrophage engulfs the antibodies and bacterium. Lysosomes fuse with the vacuole releasing the digestive enzymes that destroy the bacterium.
Explain the role of T killer cells
A bacterium infects cell of host. The cell presents the antigen and becomes an APC. T killer cell with a complimentary receptor binds to the APC. Cytokines stimulate the differentiation of the T killer cell into T killer memory cells and active T killer cells. The clones of the active T killer cells bind to infected cells presenting antigens. T killer cell release chemicals that cause pores to form in the infected cell, causing lysis. The infected cell dies.
How can one gene give rise to more than one protein?
Through post transcriptional changes to mRNA. The introns are removed leaving only the exons. This is mRNA. Before this it is called pre-mRNA when introns were still present. Once the introns are removed the exons can be spliced in many different ways leading to more than one protein.
What are the 3 ways the body is protected from infection?
Skin, stomach acid, and gut and skin flora.
How does the skin protect the body?
tough physical barrier consisting of keratin
How does stomach acid protect the body?
kills bacteria ingested
How does gut and skin flora protect the body?
natural bacterial flora competes with pathogens for food and space.
What is an example of natural passive immunity?
the crossing of mother’s antibodies through the placenta and/or breast milk
What is an example of natural active immunity?
Being exposed to or getting the disease
What is an example of artificial passive immunity?
When antibodies are injected into the body
What is an example of artificial active immunity?
when vaccinations stimulate the immune system leading to production of antibodies
What is the theory of the evolutionary race?
pathogens evolve adaptations that enable them to survive and reproduce.
How do hospitals minimise the selection pressure on bacteria?
New patients screened on arrival antibiotics only used when needed and must complete the full course. Strict hygiene regimens
What are bacteriostatic antibiotics?
Bacteriostatic antibiotics inhibit the growth of bacteria through stopping protein synthesis and production of nucleic acids so bacteria cant divide and grow.
What are bactericidal antibiotics
They kill bacteria by destroying their cell wall and thus causing them to burst (lysis)
How do you investigate the effects of antibiotics on bacterial growth?
-Sterile pipette to transfer bacteria to agar plate -Use sterile forceps to place paper discs soaked with different antibiotics. -Lightly tape lid, invert and incubate at 25C for 24-48 hrs -The larger the clear zone the more the bacteria were inhibited from growing.
