Unit 2 - Cell Structure Flashcards
Resolution definition
The distance at which two objects can be distinguished as separate
How an optical microscope works
Light passes through the specemin then through the lense to create a magnified image
How a TEM microscope works
Beam of electrons transmitted through specemin
Denser parts absorb more electrons- making them look darker
Detected on screen
How a TEM microscope works
Electron gun produces a beam of the electrons
Only some penetrate through the specemin
They then show up on the electron photomicrograph
How an SEM works
Directs a beam of electrons onto the surface of a specimen from above
Beam is then passed back in a regular pattern by the contours of the specemin
Computer forms a 3D image of the specemin
Electron microscope points (POS and NEG)
Cells killed Hard to prepare and train Artefacts occur Only in Black and White Better resolution Higher Magnification
Light microscope points
Easy to prepare and train people
Worse resolution
Limited magnification
Cell fractionation process
1) Tissue is placed in a cold isotonic buffered solution
2) Homogenisation- Tissue is placed in homogeniser
3) Filtration- Homogenate is filtered to remove solids
4) Ultra centrifugation- Pellet and supernatant
Functions of the nucleus
Contains cells hereditary material
Controls cell behaviour
Mitochondria functions
Sites of aerobic respiration
Responsible for production of ATP
Function of chloroplasts
Carry out photosythesis
Smooth endoplasmic reticulum functions
Sythesise store and transport lipids
Synthesise store and transport carbohydrates
Roles of Rough ER
Provide a large surface area for synthesis of proteins and glycoproteins
Synthesise, store and transport carbohydrates
Golgi apparatus functions
transporting, modifying, and packaging proteins and lipids
Form lysosomes
Lysosome functions
Hydrolyse material ingested by phagocytic cells
Exocytosis- Releasing enzyme to the outside of the cell
Digest worn out organelles
Autolysis- Breaks down cell after death
Ribosome function
Where protein synthesis occurs
Cell wall function
Provides mechanical strength- Stops cell bursting
Gives strength to plant as a whole
Allows water to pass through
Vacuoles Functions
Supports plants
Food store
Colour petals
Cell surface membrane function
Acts as a differentially permeable layer- controls movement in and out of the cell
Capsule definition
Secreted slime which protects the bacteria from immune system cells and helps them stick together.
Role of Circular DNA in prokaryotic cells
Contains genetic material for the cell to replicate.
Flagellum definition
Long, hair-like structure which rotates to aid movement
Plasmid definition
Small circle of DNA which is used in diverse conditions, able to replicate independently from the main DNA.
Prokaryotes can be defined by…
Lacking membrane-bound organelles (Mitochondria Lysosomes and Chloroplasts)
Smaller ribosomes
Cell wall made of muerin
Virus definition
An acellular non-living protein shell containing either DNA or RNA.
Stages of Mitosis in order
Interphase Prophase Metaphase Anaphase Telophase
Interphase
DNA replication
Prophase
Nucleolus fuses
Centrioles duplicate and move to poles, forming spindle fibres
Chromosomes become shorter and thicker
Nuclear membrane breaks down
Metaphase
Chromosomes line up on equator
Spindle fibres attach to centromeres
Anaphase
Spindle fibres contract
Centromere divides separating sister chromatids
The sister chromatids are pulled to opposite poles
Telophase
Spindle fibres disintegrate
Each chromatid is now a chromosome
Nuclear membrane reforms around each group of chromosomes
Cytokenisis- Cell divides at waist
Preparing a stained temporary mount
1) Put specemin on tile and remove thin piece of tissue
2) Add a drop of water to the slide
3) Put tissue at centre of microscope slide- make sure its not folded
4) Add stain
5) Lower an edge of coverslip onto stain- use the mounted needle held vertical with the coverslip leaning on it to slowly lower the coverslip onto the specemin.
Describe how to use an eyepiece graticule to calculate the distance across a transverse section of a leaf
1) put slide with leaf onto stage + determine which mag is appropriate
2) Replace with stage micrometer
3) Insert eyepiece graticule
4) Calculate length of each EPU
5) Put sample slide back on stage
6) Count how many EPU’s it is and multiply it by the ratio
Methods of preventing cell division for cancer
- Prevent spindle formation
- Prevent production of enzymes
Prokaryotic cell division
- Circular DNA and plasmids replicate independently
- Circular DNA attaches to the cell membrane and the cell elongates
- Circular DNA moves to opposite ends of the cell
- The cell membrane grows, dividing the cytoplasm into two
- New cell walls form between the DNA, dividing into two daughter cells
Viral replication
- Virus attackes to host cell receptor proteins
- Genetic material is released
- Genetic material and proteins are replicated by the host cell
- Viral components assemble
- Replicated viruses released from host cell
Functions of the Phospholipid bilayer
Allow lipid soluble substances to enter and leave
Prevents water- soluble substances from entering and leaving the cell
Makes the membrane flexible and self-sealing
The functions of the membrane are to
- Provide structural support
- Act as a channels transporting water soluble substances across the membrane
- Allow active transport across the membrane through carrier proteins
- Form cell- surface receptors (glycolipids)
- Act as receptors, for example hormones
The functions of cholesterol are
- To reduce lateral movement of other molecules including phospholipids
- Make the membrane less fluid at higher temperatures
- Prevents leakage of water and dissolved ions from the cell
The function of glycolipids in the membrane
- Act as recognition sites
- Help maintain the stability of the membrane
- Help cells attach to each other and form tissues
The functions of glycoproteins
- Act as recognition sites
- Help cells to attach to one another and form tissues
- Allows cells to recognise one another
Fluid mosaic model
Fluid- The induvidual phospholipid molecules can move relative to one another, this gives the membrane a flexible structure that is constantly changing shap.
Mosaic- The proteins embedded vary in shape, size and pattern
Diffusion
The net movement of molecules or ions from a region where they are more highly concerntrated to one where their concerntration is lower until evenly distributed.
Diffusion
The net movement of molecules or ions from a region where they are more highly concerntrated to one where their concerntration is lower until evenly distributed.
Osmosis definition
The passage of water from a region of high water potential to a region of low water potential through a selectively permeable membrane.
Hypotonic definition
When the solute concerntration is lower than the concerntration inside the cell
Hypertonic solution
A solution in which the solute concerntration is higher than the concerntration inside the cell. (low water concerntration)
How do pathogens cause disease?
By producing toxins
By causing damage to host cells/ tissues
Physical Barriers to pathogens
- Tears
- Nasal Hairs
- Blood clots
- Stomach acid
Phagocytosis steps
The phagocyte is atteacted to the pathogen by chemical products- moves toward pathogen
Receptor on phagocyte binds to pathogen
Phagosome is formed and lysosomes move toward the pathogen
Lysosomes release their lysozymes into the phagosome- pathogen is hydrolysed
The hydrolysis products will be absorbed/ presented on the surface/ relaesed (exocytosis)
Antigen definition
Any part of an organism or substance that is recognised as non-self and triggers an immune response
Antibody definition
They are proteins that are secreted by B lymphocytes in response to a non- self antigen
Humoral response
- There is a B cell that has a antibody complemetary to every antigen
- There is a B cell that has an antibody specific to the pathogens antibody- the two bind
- The B cell takes in the antigen and is presented on the surface by a molecule called MHC
- T cell that binds to the B cell antigen stimulates it to divide
- (Clonal expansion)- B cell divides to produce daughter cells
- Most are plasma cells which synthesise and realease antibodies
- Memory cells are produced- these remain dormant in the blood
Ways that antibodies work
Agglutination- Clumping pathogens
Antitoxins- Neutralises toxins
Lysis- Digests bacterial membrane, killing the bacterium
Opponisation- Coats the pathogen in protein- iddentifying them as foreign cells
Cell mediated response
Pathogens invade body cells or are ingested by phagocytes
Phagocyte/ infected cell places antigens from pathogens on its surface
Receptors on certain T cells are specific
This stimulates other T cells to divide rapidly by mitosis and form a clone
The cloned T cells:
Develop into memory cells
Stimulate phagocytosis
Stimulate B cells
Become cytotoxic T cells/ memory cytotoxic T cells
Give examples of passive (natural and artificial) and active (natural and artificial) immunity
Natural Passive- Antibodies in mothers milk
Artificial Passive- Antivenom
Natural Active-Response in infection
Artificial Active- Vaccination
3 types of vaccine
Dead pathogen with unaffected antigens
Weakened pathogen- Attenuation
Using purified antigens
Features of a successful vaccination programme
- Economically avaliable to immunise all the vulnerable population
- Few side effects
- Means of producing and storing it
- Means of administering it
- Must be possible to vaccinate vast majority for herd immunity
Reasons why a vaccination programme may not work
- Defective immune systems
- Induvidual may develop disease immediately after vaccination
- Pathogen mutates- antigen variability
- Too many strains to make a vaccine
- Pathogen may hide from immune system
- Induviduals may reject based on personal/ beliefs
Structure of HIV
- A core that contains RNA and some proteins (also reverse transcriptase)
- An outer protein coat called a capsid
- An extra outer layer called an envelope
- Attachment proteins on envelope
HIV replication
Attatchment protein attaches to a receptor molecule on the cell membrane of the host helper T cell
The capsid is released into the cell, where it uncoats and releases genetic material
Reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
Double stranded DNA is made and inserted into human DNA
Host cell enzymes are used to make viral proteins from viral DNA
The viral proteins are assembled into new viruses which bud from the cell
Why do antibiotics not work against viruses
Antibiotics kill bacteria by interfering with their metabolic reations
Viruses don’t have their own enzymes and ribosomes
Antibiotics can’t inhibit them
Uses of monoclonal antibodies and an example
Targeting cells- During cancer treatment
Medical diagnosis- Pregnancy testing
ELISA test outline
- Antigen is bound to bottom of the well
- Sample is added- any complementary antibodies will bind
- Secondary antibody will bind to primary antibody
- Dye that is complementary to the enzyme bounded to secondary antibody will bind if it is present
Nucleus structure features
Double membrane Outer membrane continuous with ER Nuclear pores Nucleoplasm Nucleolus- Manufacures ribosomal RNA
Mitochondria structural features
Double membrane
Cristae- Large SA for attachment of enzymes and proteins
Matrix
Chloroplast structural featurre
Double membrane
Grana- Stacks of thykaloids containing chlorophyl- high SA
Stroma- Fluid filled matrix- second step of photosynthesis
Contain DNA and 70 S ribosomes- quick manufacture of proteins
Structural features of both types of ER
3D system of sheet-like membranes
Continuous with outer membrane of nucleus
Network of tubules and cisternae
Golgi structural features
Stack of membranes- cisternae
Rounded vescicles
What are ribosomes made of
RNA and a protein
Cell wall structural features
Consists of microfibrils of polysaccaride cellulose
Embedded in a matrix
Thin middle lamella layer- cements adjacent cells together
Vacuole structure
SIngle membrane
Tonoplast membrane
Contains mineral salts, sugars and amino acids
Features of good diagram
Solid cel outline Not too much detail No crossing lines No hanging lines Not over casual Dont scetch In pencil No shading Title Magnification
Difference between cytokinesis in plant and animal cells
In Animal cells:
- Cell membrane is pulled inwards across the centre of the cell
- This separates/ pinches off the cytoplasm into two halves
In plant cells:
- Vesicles fuse to extend the cell membrane across the cytoplasm
- New cell walls develop
Order of phases in interphase
G1
S
G2
Mitosis
Cancer treatment aims
Preventing spindle formation
Preventing production of enzymes
Co transport in illeum
Sodium potassium pump pumps potassium ions into the cell by active transport
This decreases the conc gradient for sodium ions in the lumen of the ileum
Sodium ions move down conc gradient by facilitated diffusion into cell
Sodium-glucose transporter proteins carry the glucose with the sodium into the cell
Glucose then diffuses out of the cell and into blood by facilitated diffusion
Antigenic variability
An organism frequently changes antigens on their surface
Ethical issues vaccines + Monoclonal antibodies
- Vaccines require animal testing in some instances which some disagree with
- Testing vaccines on humans might make them take risks
- Some people wont take up the vaccine because of side effects but are still protected by herd immunity
- Difficult decisions have to be made about who gets what vaccine
Monoclonal antibodies are often sourced from animals and involve animal rights issues
Difference between T + B cells reacting to respective antigens
T Cells reacts to antigen presenting cell
B cell reacts to free antigen
T cell stimulates immune response (releases cytokines)
B cell reacts by releasin antibodies
Why might people have concerns about vaccinations
Side effects
Ethical concerns regarding use of animal testing
Ethical concerns around use of embryonic stem cells in testing
What is a vaccine
Cotains weakened pathogen
Stimulates production of B cells
Artificial immunity
