Topic 2 Flashcards
Cell membrane structure
Phospholipid bilayer with embedded intrinsic & extrinsic proteins
Cell membrane function
Selectively permeable barrier controls passage of substances in and out the cell
barrier between internal and external cell environments
Nucleus Structure
Nuclear pores, nucleolus, DNA and nuclear envelope
Nuclear envelope is inner and outer membrane and nuclear pores
Nucleus Function(4)
Site of transcription & pre- mRNA splicing - mRNA production
site of DNA replication
nucleolus makes ribosomes
nuclear pore allows movement of substances to/from cytoplasm
Mitochondria Structure
Double membrane with inner membrane folded into cristae
70S ribosomes in matrix
small circular DNA
enzymes in matrix
Mitochondria Function
Site of aerobic respiration
produces ATP
Chloroplast structure
Thylakoid membranes stacked to form grana, linked by lamellae
stroma contains enzymes
contains starch granules, small circular DNA and 70S ribosomes
Chloroplast function
Chlorophyll absorbs light for photosynthesis to produce organic molecules (glucose)
Organisms containing chloroplasts
Plants
Algae
Golgi apparatus stucture
Fluid-filled, membrane-bound sacs (horseshoe shaped)
vesicles at edge
Golgi apparatus function
Modifies proteins received from RER
packages them into vesicles to transport to cell membrane for exocytosis
makes lysosomes
Lysosome structure
Type of Golgi vesicle containing digestive enzymes
Lysosome function
Contains digestive enzymes
e.g lysozymes to hydrolyse pathogens/cell waste products
Rough endoplasmic reticulum function(3)
Site of protein synthesis
folds polypeptides to secondary & tertiary structures
packaging into vesicles to transport to Golgi
Smooth endoplasmic reticulum function
Synthesises and processes lipids
Cell wall function
Provides structural strength, rigidity and support to cell
helps resist osmotic pressures
Ribosome structure
Small and large subunit
made of protein and rRNA
free floating in cytoplasm & bound to RER
70S in prokaryotes, mitochondria and chloroplasts
80S in eukaryotes
Ribosome function
Site of translation in protein synthesis
Rough endoplasmic reticulum structure
System of membranes with bound ribosomes
continuous with nucleus
Smooth endoplasmic reticulum structure
System of membranes with no bound ribosomes
Cell wall structure
In plant, fungal and bacterial cells
plants - made of microfibrils of cellulose
fungi - made of chitin
bacteria - murein
Cell vacuole structure
Fluid-filled
surrounded by a single membrane called a tonoplast
Contrast prokaryotic & eukaryotic cells(5)
Prokaryotic cells are smaller
prokaryotes have no membrane bound organelles
prokaryotes have smaller 70S ribosomes
prokaryotes have no nucleus - circular DNA not associated with histones
prokaryotic cell wall made of murein instead of cellulose/chitin
Occasional features of prokaryotes
Plasmids - loops of DNA
capsule surrounding cell wall - helps agglutination + adds protection
flagella for movement
Cell vacuole function
Makes cells turgid - structural support
temporary store of sugars, amino acids
coloured pigments attract pollinators
Protein carriers
Bind with a molecule, e.g. glucose, which causes a change in the shape of the protein
this change in shape enables the molecule to be released to the other side of the membrane
Protein channels
Tubes filled with water enabling water-soluble ions to pass through the membrane,
selective,
channel proteins only open in the presence of certain ions when they bind to the protein
Features of viruses(3)
Non living and acellular
contain genetic material, capsid and attachment proteins
some (HIV) contain a lipid envelope + enzymes (reverse transcriptase)
3 types of microscopes
Optical (light) microscopes
Scanning electron microscopes (SEM)
Transmission electron microscopes (TEM)
Magnification
How many times larger the image is compared to the object
calculated by equation: Image size/actual size
Resolution
The minimum distance between two objects in which they can still be viewed as separate
determined by wavelength of light (for optical microscopes) or electrons (for electron microcopes)
Optical microscopes
Beam of light used to create image
glass lens used for focusing
2D coloured image produced
Evaluate optical microscopes(5)
Poorer resolution as long wavelength of light - small organelles not visible
Lower magnification
Can view living samples
Simple staining method
Vacuum not required
Transmission electron microscopes(5)
Beam of electrons passes through the sample used to create an image
Focused using electromagnets
2D, black & white image produced
Can see internal ultrastructure of cell
Structures absorb electrons and appear dark
Produces photomicrograph
Evaluation TEMs(6) - limitations and advantages
Highest resolving power
high magnification
extremely thin specimens required
complex staining method
specimen must be dead
vaccum required
Artefacts present in final photomicrgraph. Hard to differentiate between natural specimen and artefacts.
They are things that result from preparation of specimen
Scanning electron microscopes (4)
Beam of electrons pass across sample used to create image
focused using electromagnets
3D, black and white image produced
electrons scattered across specimen producing image
Evaluation SEMs(6)
High resolving power
high magnification
thick specimens usable
complex staining method
specimen must be dead
vaccum required
Why calibrate eyepiece graticule?
Calibration of the eyepiece is required each time the objective lens is changed
Calibrate to work out the distance between each division at that magnification
Purpose of cell fractionation
Break open cells & remove cell debris
so organelles can be studied
Homogenisation
Process by which cells are broken open so organelles are free to be separated
done using homogeniser (blender)
Homogenisation conditions
Cold reduces enzyme activity preventing organelle digestion
Isotonic prevents movement of water by osmosis - no bursting / shrivelling of organelles
Buffered resists pH changes preventing organelle + enzyme damage
Ultra- centrifugation
Homogenate solution filtered to remove cell debris
solution placed in a centrifuge which spins at a low speed initially
then increasingly faster speeds to separate organelles according to their density
Differential centrifugation
Supernatant first out
(spun at lowest speed) is most dense = nuclei
spun at higher speeds
chloroplasts -> mitochondria -> lysosomes -> RER/SER -> ribosomes (least dense)
Binary Fission
Involves circular DNA & plasmids replicating
cytokinesis creates two daughter nuclei
each daughter cell has one copy of circular DNA and a variable number of plasmids
Cell cycle
1) Interphase (G1, S, G2)
2) nuclear division - mitosis or meiosis
3) cytokinesis
Interphase
Longest stage in the cell cycle
G0 phase - resting phase in which the cell is neither replicating or preparing to divide.
G1 phase - cells grows in size and synthesizes mRNA and protein required orDNA synthesis.
S phase - DNA replication and much of DNA repair activity occurs in cell
DNA replicates and appears as two sister chromatids held by centromere
G2 phase - cell prepares for mitosis
Also has checkpoints
Mitosis
One round of cell division
two diploid, genetically identical daughter cells
growth and repair (e.g. clonal expansion)
comprised of prophase, metaphase, anaphase and telophase
Prophase
Chromosomes condense and become visible
nuclear envelope disintegrates
in animals - centrioles separate & spindle fibre structure forms
Metaphase
Chromosomes align along equator of cell
spindle fibres released from poles now attach to centromere and chromatid
Anaphase
Spindle fibre contracts (using ATP) to pull chromatids, centromere first, towards opposite poles of cell
centromere divides in two
Telophase
Chromosomes at each pole become longer and thinner again
spindle fibres disintegrate + nucleus reforms
Mitotic index
Used to determine proportion of cells undergoing mitosis
Calculated as a percentage OR decimal
Mitotic index = the total no. of cells in mitosis/ the total no. of cells
x100 for percentage
Fluid mosaic model
Describes the lateral movement of membranes - gives fluid structure
with scattered embedded intrinsic and extrinsic proteins
membrane contains glycoproteins, glycolipids, phospholipids and cholesterol
Phospholipids in membranes
Phospholipids align as a bilayer
hydrophilic heads are attracted to water
hydrophobic tails repelled by water
Cholesterol
Present in eukaryotic organisms to restrict lateral movement of the membranes
adds rigidity to membrane- resistant to high temperatures & prevents water + dissolved ions leaking out
Selectively permeable membrane
Molecules must have specific properties to pass through plasma membrane
lipid soluble (hormones e.g. oestrogen)
very small molecules
non-polar molecules (oxygen)
Simple diffusion
Net movement of molecules from an area of higher concentration to an area of lower concentration
until equilibrium is reached
passive
Facilitated diffusion
Passive process using protein channels/carriers
down the concentration gradient
used for ions and polar molecules e.e sodium ions
and large molecules e.g. glucose
Osmosis
Net movement of water
from an area of higher water potential to an area of lower (more negative) water potential
across a partially permeable membrane
Water potential
The pressure created by water molecules
measured in kPa and represented by symbol ψ
pure water has a water potential of 0kPa
the more negative the water potential, the more solute must be dissolved
Hypertonic solution
When the water potential of a solution is more negative than the cell
water moves out of the cell by osmosis
both animal and plant cells will shrink and shrivel
Hypotonic solution
When the water potential of a solution is more positive (closer to zero) than the cell
water moves into the cell by osmosis
animal cells will lyse (burst)
plant cells will become turgid
Isotonic
When the water potential of the surrounding solution is the same as the water potential inside the cell
no net movement in water
cells would remain the same mass
Active transport
The movement of ions and molecules from an area of lower concentration to an area of higher concentration using ATP and carrier proteins
carrier proteins act as selective pumps to move substances
Role of carrier protein in active transport
When molecules bind to the receptor - ATP will bind to protein on inside of membrane and is hydrolysed to ADP/ Pi
protein changes shape and opens inside membrane
Co-transport
The movement of two substances across a membrane together, when one is unable to cross the membrane itself
involves a cotransport protein
involves active transport
e.g. absorption of glucose/amino acids from lumen of intestines
Molecules lymphocytes identify
Pathogens (bacteria, fungi, viruses)
cells from other organisms of same species (transplants)
abnormal body cells (tumour cells)
toxins (released from bacteria)
Antigens
Proteins on the cell-surface membrane
trigger an immune response when detected by lymphocytes
Antigenic variability
When pathogenic DNA mutates causing a change in shape of antigen
previous immunity is no longer effective as memory cells don’t recognise new shape of antigen.
Specific antibody no longer binds to new antigen
Physical barriers
Anatomical barriers to pathogens-
skin
stomach acid
lysozymes in tears
Phagocytes
Non-specific immune response
phagocytes become antigen- presenting cells after destroying pathogen
T lymphocytes
Made in bone marrow and mature in thymus gland
Involved in cell-mediated immune response
Only respond to antigen-presenting cells(own body cells)
Antigen- presenting cells. 4 types of
Any cell that presents a non-self antigen on their surface
infected body cells
macrophage after phagocytosis
cells of transplanted organ
cancer cells
Role of T helper cells
Have receptors on their surface that attach to antigens on APCs
become activated - clonal selection
Role of cloned T helper cells (4)
Some remain as helper T cells & activate B lymphocytes
stimulate macrophages for phagocytosis
become memory cells for that shaped antigen
become cytotoxic killer T cells
Cytotoxic T cells
Destroy abnormal / infected cells by releasing perforin (membrane permeable)
so that any substances can enter or leave the cell and this causes cell death
B lymphocytes
Made in bone marrow and mature in bone marrow
involved in humoral immune response
involves antibodies
Humoral response
B cells have antibodies and receptors on their surface and so when they come in contact with complementary antigen they engulf the pathogen by endocytosis.
Process antigens and presents it on its surface.
This B cell acts as APC and if it comes in contact with a T helper cell with complementary receptor.
This stimulates B cells to undergo clonal selection and expansion - rapid division by mitosis.
differentiate into plasma cells / memory B cells
plasma cells make antibodies
B memory cells
Derived from B lymphocytes
Remember specific antibody for particular antigen
Will rapidly divide by mitosis and differentiate into plasma cells upon secondary encounter Resulting in large numbers of antibodies rapidly
Antibodies
Quaternary structure proteins made of four polypeptide chains
different shaped binding site = variable region
complementary to a specific antigen
Antibody structure. Draw it
Labels -
2 heavy and light chain
Constant and variable region
Antigen binding sites
Agglutination
Antibodies have two binding sites and are flexible - clumps pathogens together
makes it easier for phagocytes to locate and destroy pathogen
Passive immunity
Antibodies introduced into body
plasma and memory cells not made as no interaction with antigen
short-term immunity
fast acting
Active immunity
Immunity created by own immune system - antibodies made
exposure to antigen
plasma and memory cells made
long term immunity
slower acting
Natural active immunity
After direct contact with pathogen through infection
body creates antibodies and memory cells
Artificial active immunity
Creation of antibodies and memory cells following introduction of an attenuated
pathogen or antigens
vaccination (oral or injection)
Vaccinations
Small amounts of dead or attenuated pathogens injected / ingested
humoral response activated
memory cells are able to divide rapidly into plasma cells when re-infected
Primary vs Secondary response
Primary = first exposure to the pathogen
longer time for plasma cell secretion & memory cell production
for the secondary response, memory cells divide rapidly into plasma cells
so a large number of antibodies made rapidly upon reinfection
Herd immunity
When enough of the population is vaccinated so pathogen is not transmitted and spread easily Provides protection for those without vaccine - vulnerable ones
Monoclonal antibodies
A single type of antibody that can be isolated and cloned
antibodies that are identical - from one type of B lymphocyte
complementary to only one antigen
Uses of monoclonal antibodies
Medical treatment - targeting drugs by attaching antibody complementary to tumour cell antigen. Direct and indirect monoclonal antibody.
medical diagnosis - pregnancy tests
Pregnancy test
ELISA test which uses 3 monoclonal antibodies and enzymes to test for hCG
Explain in detail
Purpose of ELISA test
Detect the presence and quantity of an antigen
used for medical diagnosis. Eg., HIV
Ethical issues with monoclonal antibodies
Requires mice to produce antibodies and tumour cells
requires a full cost-benefit analysis
HIV structure
Core = RNA and reverse transcriptase
capsid = protein coat
lipid envelope taken from hosts cell membrane
attachment proteins so it can attach to Helper T cells
HIV replication
Attaches to CD4 receptor on helper T cells
protein fuses with membrane allowing RNA + enzymes to enter
reverse transcriptase makes DNA copy and this is inserted into nucleus
nucleus synthesises viral proteins
Destroys T helper cells
Auto Immunodeficiency Syndrome (AIDs)
When HIV has destroyed too many T helper cells, host is unable to produce adequate immune response to other pathogens
host susceptible to opportunistic infections eg TB and cancer
Role of antibodies in ELISA
First antibody added is complementary to antigen in well - attaches
second antibody with enzyme added which attaches to first antibody as complementary. when substrate solution added enzyme can produce colour change
Why vaccines may be unsafe(4)
Inactive virus may become active - viral transformation
non-pathogenic virus can mutate and harm cells
side effects of immune response
people may test positive for disease
Why are antibiotics ineffective against viruses?
-Antibiotics work by inhibiting certain enzymes involved in creating peptide cross linkages in cell wall which -makes the cell wall weak and therefore cannot withstand pressure when water enters and cell dies
-Viruses are inside host cells where antibiotics cannot reach
-antibiotics affect parts of bacteria that viruses do not have (e.g the cell wall)
-Virus lack their own metabolic pathway and cell structures and they contain protein coat rather than peptidoglycan or murien cell wall
Why do you wash well in ELISA
Removes unbound 2nd antibodies
otherwise enzyme may be present→ colour change → false positive
Pathogens
Microorganisms that cause a disease
by releasing toxins or killing cells / tissues
Cytokinesis
Final stage in the cell cycle when the cytoplasm splits in two
creates two new cells
Uncontrolled mitosis
Uncontrolled cell division can lead to the formation of tumours and of cancers
many cancer treatments are directed at controlling the rate of cell division
Viral replication
Following injection of their nucleic acid
the infected host cell replicates the virus particles
Cell adaptations for rapid transport across membranes?
Increase in surface area or membrane
increases in the number of protein channels and carrier molecules in the membranes
Antigen- antibody complex
When a complementary
antibody binds to an antigen
this clumps pathogens together (agglutination)
Why is the high resolution of TEM not always achieved?
-difficulties preparing specimen will limit resolution that can be achieved
-higher energy beam is required which may destroy the specimen
Osmosis and plant cells
When water enters plant cell by osmosis - it enters protoplast and protoplast pushes against the cell wall and plant cell becomes turgid.
When water leaves plant cell it moves out of protoplast and it stops pushing against cell wall and this is called incipient plasmolysis.
When more water leaves the protoplast pulls away from cell wall and the cell structures start to shrink and this is called plasmolysis
Why is high concentration of glucose ORS for people with diarrhoea not good
As glucose increases solute concentration in lumen causing more water to leave epithelial cells which worsens dehydration
How is monoclonal antibodies produced outside body and modified for use in humans (7)
-Mice exposed to non self cell antigen for which antibody is required
-mice produces mixture is antibodies which is extracted from the spleen of the mice
-its then mixed with cells that divide readily outside body - cancer tumour cell
-detergent is added to this mixture to break down the cell membrane so both structure can join and this produces HYBRIDOMA cell
-theses cells are then separated under microscope and each cell grown in culture to see if they process the desired antibody
- the ones which produces the desired antibody is grown in large scale and these antibodies are called monoclonal antibody as its produced from a single B cell
-As it’s made of mice cells its modified to make it like human cells before being used on humans and this process is called Humanisation
Features of successful vaccination programs
-economically viable and sufficient vaccine available to vaccinate the vulnerable population - herd immunity
-Means of administering it at an appropriate time eg trained staffs
-Means of storing, transporting and production available eg hygienic conditions
-few side effects as this may make people opt out
How do drugs used in chemotherapy work
They prevent DNA replication
Inhibition metaphase stage by interfering with spindle formation
Indirect active transport for absorption of amino acids and glucose in ileum
1-Na+ actively transported out of epithelial cells by sodium potassium pump. Takes place in a different type of carrier protein.
2-Thus maintains concentration gradient between lumen and epithelial cells as there is high concentration of Na+ in the ileum compared to epithelial cells
3-So Na+ moves down the concentration gradient into epithelial cells using co transport protein as it carries either amino acids or glucose into the epithelial cells.
4- the glucose or amino acid moves into blood plasma by facilitated diffusion using different type of carrier protein
5-Na+ is down the concentration gradient while glucose/amino acid is against. It’s the movement of Na+ down the concentration gradient rather than ATP which drives this process
Why is active transport required in the ileum along with diffusion for absorption of glucose and amino acid
-Carbohydrates and amino acids continuously being digested so high concentration in the lumen always. And in the blood glucose always used up as it’s transported around and used in respiration.
-Therefore concentration gradient established and glucose and amino acids can diffuse by facilitated diffusion into blood.
-But diffusion is only till equilibrium is reached, so for moving and absorbing of all the glucose and amino acids is done using active transport against the concentration gradient
How is rate of absorption in ileum increases
-Epithelial cells contains villi which contains micro villi which increases the surface area for absorption
-Increasing surface area increases no. of carrier proteins and channels therefore increasing absorption
