Synoptic Flashcards
How do pathogens cause disease
-produce toxins
- pathogens replicate inside and destroy host cells
Antigen
- protein that stimulates an immune response which results in the formation of a specific antibody(antibody generator)
-if the antigens are recognised as not self it will initiate an immune response
What is a phagocyte
- white blood cells which engulf and destroy any cell with a non self antigen in a process called phagocytosis
Describe phagocytosis
- pathogen is engulfed by the phagocyte
-engulfed pathogen enters the cytoplasm of the phagocyte in a vesicle called phagosome
-lysosomes fuse with hydrolytic enzymes hydrolysing the pathogen - waste material are released by exocytosis and antigens are presented on the the cell membrane and the phagocyte becomes antigen presenting cell
Role of Th helper cells
-Specific TH cell binds to the antigen presenting cell
-Release cytokines that attract phagocytes to the area of infection.
-Release cytokines that activate Cytotoxic Killer T cell (TC).
-Activates a specifically complementaryB cell.
-Form memory THcells
Role of Tc cells ( cytotoxic killer cell )
-Locate and destroys infected body cells that present the correct antigen.
-Binds to antigen-presenting-cells
-Releases perforin (protein) which creates holes in the cell surface membrane which destroys the APC.
Plasma cells
Produce and secrete vast quantities of specific antibodies into the blood plasma
Memory B Cells
Remain in the body to respond to pathogen rapidly and extensively should there be a future re-infection
Describe the structure of an antibody
Antibodies are complex proteins with a quaternary structure (4°) ,made up of four polypeptide chains. The overall shape of the antibody is “Y-shaped”
Antibody
Protein made in response to foreign antigen – has binding sites which bind specifically to an antigen. A specific antibody is produced by a specific ‘Plasma cell’.
Describe the regions in a antibody
-The main part of the antibody is the same in all antibodies this is the constant region
- variable region has a different primary structure therefore different tertiary structure
The variable region and therefore the binding site which is specific and different for each antibody
How do antibodies assist in the destruction of pathogens?
1) AGGLUTINATION: Specific antibodies bind to the antigens on pathogen and clump them together.
2) OPSONISATION: marking pathogens so phagocytes recognise and destroy the pathogen more efficiently.
3) LYSIS: Bind to antigens and lead to destruction of the pathogen’s membrane.
4) ANTI-TOXIN & ANTI-VENOM: Bind to toxins or venom (both usually proteins) to prevent these molecules from binding to their complementary target receptors.
5) Prevent pathogen replication
Secondary response
The activation of memory cells to produce antibodies
Secondary response
-The secondary response is both RAPID and EXTENSIVE.
-activation of memory cells to produce antibodies
Antigenic variability
Some pathogens have antigens which mutate and change shape (e.g. Flu, HIV).
When this occurs, the pathogen will not be recognised by the memory cells from the previous infection, (no longer complementary to receptors) and the individual will not be able to initiate a secondary response.
Two types of immunity
- passive :No exposure to ANTIGEN. Antibodies are received from elsewhere i.e. are not produced by the individual. Can be given by mother or an antiserum (injection of antibodies). No production of Memory cells
-active: Antibodies produced in response to exposure to an ANTIGEN. This type of immunity is provided by the memory cells that are produced after a primary immune response to a pathogen.
What are vaccine not effective to
Pathogen that shows antigenic variability
Process of vaccination
The pathogen is engulfed by a phagocyte and displayed on an antigen-presenting cell.
A specific T helper cell binds to the antigen on the antigen presenting cell.
The specific T helper cell stimulates a specific B cell (by releasing cytokines).
B cell divides by mitosis to produce plasma cells and memory cells.
Plasma cells produce and release antibodies
Memory cells recognise the antigen on second infection.
What’s herd immunity
If enough individuals in the population are vaccinated (85%), then there is little chance of the disease spreading, therefore even non-vaccinated individuals will be protected.
Ethical issues of vaccination
Human testing
Animal testing
Availability
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how
- Vaccine contains antigen from pathogen;
- Phagocyte/macrophage presents antigen on its surface.
- Specific T helper cell with specific receptor binds to complementary antigen.
- T helper cell stimulates specific B cell.
- (With) complementary antibody on its surface.
- B cell divides by mitosis to form plasma cells.
- plasma cells secretes large amounts of antibody
- Formation of Memory B cells with complementary antibodies remain in the blood
Describe the difference between active and passive immunity.(comparison)
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells/memory cells;
- Passive involves antibody introduced into body from outside/named source;
- Active long term, because antibody produced in response to antigen;
- Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop/work, passive fast acting;
Describe the structure of HIV
RNA as genetic material
Contains reverse transcriptase
Protein capsid attachment proteins
Has a phospholipid envelope
HIV replication
- Protein on HIV binds with a protein commonly found on TH cells.
- Capsid fuses with cell-surface membrane and releases Viral RNA and enzymes into the helper TH cell.
- The HIV’s reverse transcriptase converts viral RNA into cDNA using host nucleotides.
- Viral cDNA moves into nucleus of T cell and is inserted into host cell genome (DNA). The person is now INFECTED.
- Transcription of viral DNA into (viral) mRNA which is translated to produce HIV proteins. The infected TH cell starts to manufacture new HIV virions / particles.
- Particles break away from TH cell with a section of host cell surface membrane which forms their lipid envelope, with TH receptor proteins embedded (to gain access into more TH cells).
- Over time this leads to a reduction in the number of TH cells or reduction by inactivation of TH cells.
AIDS (more or less)
• More HIV
• Destruction of more TH cells
• Less activation of (specific) TC / B cell
• Less able to destroy (other) pathogen / Cancerous / Infected cell
How do antibiotics work
• Antibiotics work by preventing bacteria making a normal cell wall (murein/peptidoglycan) by targeting 70s ribosomes (not cytoplasmic 80S ribosomes found in Eukaryotes).
• This means that the bacteria are unable to resist osmotic pressure and the cells burst due to an increase in cell volume of water by osmosis.
• Viruses use host cells organelles to carry out metabolic activities so do not have any viral organelles to disrupt.
• Viruses also have a CAPSID (protein coat) rather than a murein cell wall. This does not allow antibiotics to act on viruses as they do for bacteria.
• As viruses spend most of the time within a host cell, they are also out of reach of antibiotics.
Smooth endoplasmic reticulum
Recombines glycerol and fatty acids to make triglycerides
Packages triglycerides into vesicles and transports them into Golgi
Rough endoplasmic reticulum
Synthesis and transports proteins throughout the cell
Ribosomes
-site of protein synthesis
-consists of large and small subunit (rRNA subunits)
- contains 80s ribosomes
Golgi apparatus
sorts, modifies and packages proteins and triglycerides into vesicles.
Exons
Code for amino acid sequences
Introns
Non coding sequences
Genome
Complete set of genes in a cell
Proteome
Full range of proteins that a cell is able to produce
Compare the structure of mRNA and DNA
DNA is double stranded whereas is single stranded
DNA is longER whereas RNA is shortER
Thymine in DNAwhereasReplaced with uracil in RNA
Deoxyribose in DNA whereas Ribose in RNA
DNA has hydrogen bonds whereas mRNA doesn’t have hydrogen bonds
DNA has introns whereas mRNA doesn’t have introns
Describe transcription
- (DNA Helicase) Hydrogen bonds are broken so strands separate;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- (Attraction) according to base pairing rule Adenine-Uracil, Cytosine-Guanine:
- RNA polymerase joins (RNA) nucleotides together forming phosphodiester bonds through condensation reactions;
- Pre-mRNA spliced to remove introns (Eukaryotes).
Describe translation
- mRNA binds to ribosome;
- Ribosome finds the START codon;
- Idea of two codons/binding sites;
- (Allows) tRNA with complementary anticodons to bind/associate with codon;
- (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules) using energy from ATP;
- tRNA released as Ribosome moves along (mRNA to the next codon)/translocation described;
- Ribosome releases polypeptide into RER when the STOP codon is reached.
What does universal mean
the same 3 bases on mRNA / DNA (CODON / TRIPLETS) code for the same amino acids in all orgnisms
Non overlapping
Each base is only part of 1 triplet / codon.
So during translation the ribosome reads each base only once in the codons on the mRNA – the first three bases are read, followed by the second three bases, then the third three bases, and so on, in sets of three.
Degenerate
More than one triplet (DNA)/ codon (mRNA) codes for an amino acid.
Consequence of a gene mutation
-may alter the primary structure of the polypeptides which affects the sequence of amino acids in a polypeptide
-this may alter the secondary structure therefore changing the position of the weak hydrogen bonds affecting alpha helices ands beta pleated sheets
-it may also alter the tertiary structure which changes the position of the weak hydrogen,ionic and disulphide bridges bonds.It may also alter the binding site or active site of enzymes and make the protein non-functional
List mutagenic agents
-High energy ionising radiation such as gamma or x rays
-DNA reactive chemicals such as benzene
- biological agents such as some viruses or bacteria
Gene pool
The number of different alleles of a gene in a population
Define Natural selection
A process by which organisms that are better adapted to their environment survive and reproduce in greater numbers ,resulting in the increase of the frequency of the advantageous allele within the population
Natural selection(order)
-variations exists within a population due to mutations
-better adapted individuals are more likely to survive and pass on their alleles
-those which are less adapted fail to survive and reproduce
-these organisms are less likely to pass on their alleles
-organisms are also subject to selection pressures.They determine the spread of allele within the gene pool, they can also be biotic or abiotic
Stabilising selection
-occurs in a stable environment
-selection pressures at both ends of distribution
-favours the average and tends to eliminate the extremes
Directional selection
-favours the extreme phenotype
-over time the phenotype may shift
Relationship between surface area to volume ratio and the size of an organism
-surface area to volume ratio decreases as an organism gets larger
As surface area to volume ratio decreases as an organism gets larger what happens to the heat loss
Larger organism loses heat more slowly across its organism than a smaller organism
Define Ficks law
Rate of diffusion=sa x concentration gradient divided by the diffusion pathway
Characteristics of a good exchange system
-large surface area
-large conc gradient
-thin exchange surface
Movement of oxygen through an insect
-oxygen enters the insect through spiracls and into the tracheae.Spiracles close.
-oxygen diffuses through the trachea into the tracheoles down a concentration gradient.
-oxygen is delivered directly to the respiring tissues
What does abdominal pumping does
Increases the rate of gas exchange
Getting additional oxygen during flight
-during flight insect may partially respire anaerobically producing lactic acid
-this lowers water potential of the muscle cellls.As lactate builds up , water passes via osmosis from the tracheaoles into the muscles
Explain 3 ways in which an insects tracheal system is adapted for efficient gas exchange
-tracheoles have thin walls so short diffusion distance
-large numbers of tracheoles so large sa for gas exchange
-spiracles closing and opening to maintain a concentration gradient
Explain two ways in which the structure of fish gills is adapted for efficient gas exchange
-many filaments so large SA
-lamellae are thin for a short diffusion pathway
Explain the counter current mechanism
-water and blood flow in opposite directions
-blood always passes water with higher oxygen concentration
-concentration gradient is maintained
Adaptations of a leaf for gas exchange
-flat so provides big SA to volume ratio
-many stomata so pores allow air to move in and out
Adaptations to reduce water loss
-waxy cuticle
-stomata distributed on the lower surface
-at night the guard cells close the stomata to prevent water loss
Adaptations of Xerophytic plants
-reduced number of stomata =less surface area for water loss
-stomata in pits=reduced concentration gradient
-rolled leaves=reduced conc gradient
Describe how carbon dioxide in the air outside the leaf reaches mesophyll cells inside the leaf
-enters via stomata
-stomata is opened by guard cells
-diffuses through air spaces
-down a concentration gradient
Lysosomes
-used to hydrolyse damaged or worn-out organelles,by using hydrolytic enzynes
Centrioles
Form a network of spindle fibres which pull chromosomes/chromatids apart
Contrast plant cell vs animal cells
Cellulose cell wall - no cell wall
Chloroplast present-no chloroplast
Large central vacuole-no
Carbs stored as starch-carbs stored as glycogen
No centrioles -centrioles
Granum
Stack of thylakoid membranes
Thylakoid membrane
Contains chlorophyll for photosynthesis and atp synthase enzyme to produce atp
Stroma
Fluid filled part
Function of the chloroplast
-absorb light energy and converts it to chemical energy
Compare prokaryotic cell to eukaryotic cell
-dna is circular whereas dna is linear
- contains no member bin organelles whereas it contains membrane bound organelles
-contains 70s ribosomes whereas it contains 80 s ribosomes
-some have capsules whereas no capsule
-cell wall made of Murein or peptodoglycan where as cell wall is made of cellulose
Two types of electron microscopes
-tem
-sem
TEM electron microscope
-electrons pass through the specimen
-specimens are fixed in resin and are extremely thin so must be dead
-Specimens must be in a vacuum so they must be dead
Principles and Limitations of TEM
Principles:
1. Electrons pass through / enter (very thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
cell structure.
4. Electrons have short wavelength so give high resolution;
Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present
8. Complex staining method / complex / long preparation time
Two structures which can be identified using TEM
Mitochondria
Lysosome
Ribosome
Give one advantage of using a TEM rather than a SEM.
Higher resolution / higher (maximum) magnification / higher detail (of image);
OR
Allows internal details / structures within (cells) to be seen / cross section to be taken;
Give one advantage of using a SEM rather than a TEM.
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
Explain the advantages and limitations of using a TEM to investigate cell structure.
Advantages:
1. Small objects can be seen;
2. TEM has higher resolution;
3. Wavelength of electrons shorter;
Limitations:
4. Cannot look at living cells;
5. Must be in a vacuum;
6. Must cut section / thin specimen;
7. Preparation may create artefacts (false image);
Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope.
1.Add a drop of water to the microscope slide;
2. Get a thin section of plant tissue and float on the drop of water;
3. Stain with KI solution;
4. Lower the cover slip using a mounted needle to avoid air bubbles;
Cell fractionation and differential centrigufation
-the tissue is homogenised in a blender in a ice cold, isotonic buffered solution to break open the cells releasing the organelles
=ice cold to reduce the action of enzymes that would digest organelles
=isotonic to prevent osmosis if water in the organelles so they don’t burst
=buffered to stop ph changes which would denature proteins
-mixture is filtered to remove cellular debris
-supernatant is centrifuged at higher speed and longer period of time to remove the densest organelle
Biodiversity
The number of species and the nu,bear of individuals of each species within one community
Species richness
The number of different species in a community
Community
All the individuals of all species living together in the same area at the Same time
Species
Group of similar organisms with the same genes which reproduce to produce fertile offspring’s
Genetic diversity
Difference in dna
Niche
An organism role within an ecosystem
It describes how the specie behaves,interacts with other organisms and responds to the environment
Habitat
A player where an organism normally lives within an ecosystem
What information is required to calculate an index of diversity
Number of species and theirs abundance
Economic arguments for maintaining biodiversity
-medical
-tourism
-agriculture
The order of the classification system
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Hierarchy
Groups within groups
No overlap
List few ways in which courtship behaviour increases the probability of successful mating
-attracts the same species
-attracts opposite sex
-indicates sexual maturity
-stimulates release of gametes
-forms a pair bond
Modern classification methods
-observable characteristics
-base sequence of dna
-base sequence of mRNA
-the amino acid base sequence
Structure of haemoglobin
Complex protein with a quaternary structure
Has 4 oxygen molecules
Percentage saturation
Amount of oxygen combined in the heamoglobin
Partial pressure of oxygen
Amount of oxygen in a mixture of gases or a solution
Affinity
Natural attraction to something
Cooperative oxygen loading
The first o2 molecule alters the tertiary structure of the haemoglobin molecule exposing the 2nd and 3rd o2 binding site which make it easier to bind and load
Explain the advantage of the curve for a foetus
Higher affinity/loads more oxygen at high partial pressure
Oxygen moves from mother to foetus
Explain how oxygen is loaded,transported and unloaded in the blood
-haemoglobin carries oxygen in red blood cells
-association occurs In the lungs at high partial pressure
-dissociation occurs in the respiring tissues
-unloading is linked to high carbon dioxide concentration
Parts of interphase
G1= cell increases in size and new biomass is made
S phase= DNA replicates by semi-conservative replication
G2 phase=cells get ready for division
Chromosome
Independent dna molecule which has been supercoiled into a condensed form
Gene
Section of dna that codes for one specific polypeptide
Homologous chromosome
Have the Same genes in the same loci
Uses of mitosis
-replacement of worn out or dead cells
-repair of damaged tissue
-increase cell numbers and growth of an organism
Prophase
Chromosomes=supercool and become visible
Metaphase=chromosomes line up on the equator of cell
Anaphase=spindles get shorter, centromere slits identical sister chromatids separate
Telophase= two nuclei are formed
Describe the appearance and behaviour of chromosomes during mitosis:
- During prophase, chromosomes supercoil and condense to become visible;
- Chromosomes appear as 2 identical sister chromatids joined by a centromere;
- During metaphase chromosomes line up on the equator of the cell;
- Chromosomes attach to the spindle fibres;
- By their centromeres;
- During anaphase, the centromere splits;
- Sister chromatids are pulled to opposite poles of the
cell making a V shape; - During telophase, chromatids uncoil and become
thinner;
How do bacteria replicate
Binary fission
Describe binary fission
replication of the circular DNA (not associated with histones) and of plasmids
• division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.
Mitotic index
Number of cells with condensed chromosomes divided by total number of cells
Serial dilution
M1 x v1=m2 x v2
Why happens during crossing over
- The homologous chromosomes associate (Bivalent is formed).
- Chiasmata form(Chromosomes entangle / twist).
- Equallengthsof(non-sister) chromatids / alleles are exchanged.
- Producing new combinationsof alleles.
Describe and explain the processes that occur during meiosis that increase genetic variation. [5
- Homologous chromosomes pair up/ bivalents form;
- Independent segregation occurs;
- Maternal and paternal chromosomes are reshuffled
in any combination; - Crossing over leads to exchange of parts of (non-
sister) chromatids/alleles between homologous
chromosomes; - (both) create new combinations of alleles.
