Cells Flashcards
The structure of eukaryotic cells
Cell-surface membrane.
Nucleus (containing chromosomes, consisting of protein-bound,
linear DNA, and one or more nucleoli)
mitochondria.
Chloroplasts (in plants and algae).
Golgi apparatus and Golgi vesicles
lysosomes (a membrane-bound organelle that releases hydrolytic enzymes). Ribosomes.
Rough endoplasmic reticulum and smooth endoplasmic reticulum.
Cell wall (in plants, algae and fungi).
Cell vacuole (in plants).
Organisation of specialised cells
Cells into tissues, tissues into organs and organs into systems.
The structure of prokaryotic cells
Cytoplasm that lacks membrane-bound organelles.
Smaller ribosomes.
Single circular DNA molecule that is free in the cytoplasm and is not associated with proteins.
Cell wall that contains murein, a glycoprotein.
One or more plasmids.
A capsule surrounding the cell.
One or more flagella.
The structure of viruses
Genetic material, capsid and attachment protein.
Magnification
How many times bigger the image is in comparison to real object size
Resolution
The ability to distinguish between two objects
Definition of diffusion
The net movement of molecules or ions from a region of high concentration to a region of low concentration
What is facilitated diffusion?
Diffusion which transports large and polar molecules across membrane, facilitated by transmembrane channel and carrier proteins.
What is osmosis?
Movement of water molecules from a region of higher water potential (less negative) to a region of lower water potential (more negative) across a partially permeable membrane
What is active transport?
Movement of molecules or ions across the membrane against the concentration gradient from a lower region of concentration to a higher concentration, requiring ATP
Definition of antigen
Part of organism which is recognised as foreign by immune system, often embedded in cell surface membrane or cell of invading cells.
Definition of antibody
Proteins which form a vital part of bodys defense system. Produced by B lymphocytes by the presence of an complementary antigen.
Antibody structure
Made up of four polypeptide chains
Two variable regions
Two constant regions
Ethical issues of monoclonal antibodies
- Animal testing
- Animal based substances
-Testing on humans potentially putting them at risk
Role of helper T cells
Stimulates cytotoxic T cells (Tc cells), B cells and phagocytes
Importance of vaccines
To provide protection for individuals and populations against disease by stimulating immune system to produce specific antibodies and memory cells to ensure efficient destruction of pathogen if it ever entered body.
Virus cell division
Being non-living, viruses do not undergo cell division. Following injection of their nucleic acid, the infected host cell replicates the virus particles.
Mitosis
Cell division resulting in two genetically identical daughter cells
Formation of tumours and cancers
Uncontrollable cell division
Controlled cell division process
Mitosis
Cell fractionation
The process where cells are broken up and the different organelles they contain are separated out
Microscopy
The process of producing a magnified image of an object using the instruments of microscopes
Solution for cell fractionation properties
Ice cold- reduce enzyme activity which may break down organelles
Buffered- prevents change in pH affecting organelles
Isotonic- prevent having an osmotic effect
Stages of cell fractionation
Homogenation
- breaking up of cells in homogeniser, resultant fluid (homogenate) filtered to remove large debris
Ultracentrifugation
- separation of fragments in homogenate in a centrifuge machine
Limits to optical microscope
The resolution would be low as light has a long wavelength
Process of ultracentrifugation
- Filtrate placed in centrifuge and spun at lowest speed, heaviest organelles (nuclei) forced to bottom of tube forming a pellet
- Supernatant removed and transferred to another tube and spun in centrifuge at a faster speed forcing down next heaviest organelles
- Process continues till desired organelle is separated
Advantages of electron microscope invention in the 1930s
- Short wavelength for electron beam so high resolution
- Electrons are negatively charged so beam can be focused using electromagnets
Two types of elctron microscope
Transmission Electron Microscope
Scanning Electron Microscope
TEM
Use electromagnets to focus a beam of electrons which are transmitted through specimen
Advantages of TEM
-High resolution images
- Show internal structures of organelles
LImitations of TEM
- Extremely thin specimen needed for electrons to pass
- Dead specimen as process happens in a vacuum
- 2D images
SEM
Scan a beam of electrons across surface of specimen, knocking electrons gathered on cathode ray to form image
Cell specialisation
In multicellular organisms, cells become specialised for specific functions through a process known as differentiation
Stages of cell cycle
Interphase, Prophase, Metaphase, Anaphase, Telophase (cytokinesis)
Importance of mitosis
Growth, repair, reproduction
Treatment of cancer
Chemical drugs (chemotherapy) used to disrupt cell cycle
- preventing DNA replication
- Inhibiting metaphase by interfering with spindle
Radiotherapy
- Damage DNA in cancer cell
What is simple diffusion?
Movement of small and non polar molecules to a lower region of concentration, particles randomly in motion due to kinetic energy
Structure of HIV
Lipid envelope (derived from the cell membrane of the host helper T cell) with attachment proteins embedded in.
Capsid protein coat.
Core which holds genetic material.
Proteins (including the enzyme reverse transcriptase).
Replication of viruses
Virus uses attachment protein to bind to complementary receptors on host cell’s plasma membrane. Genetic material released into cells. Reverse transcriptease takes place. Viral particles will be produced and cause host cell to burst through a lyctic release where virus moves to new cells and tisues.
HIV formation into AIDS
When an HIV virus infects a helper T cell and replicates, the cells are killed.
As HIV spreads through the body and more helper T cells are killed, the immune system weakens.
The weak immune system makes the individual highly susceptible to infection by other pathogens. This is AIDs.
HIV full name
Human Immunodefiency Virus
AIDS full name
Acquired Immunodeficiency Syndrome
What does ELISA stand for?
Enzyme Linked Immunosorbant Assay
What are channel proteins?
Allow specific charged particles to pass across membrane.
What are carrier proteins?
They bind to specific molecule and change their shape allowing molecule to enter cell, protein would then return to shape.
Isotonic
Equal water potential either side of membrane
Hypotonic
Solution has higher water potential than inside of cell
Animal cell- cell swells and cytosis occurs
Plant cell- cell swells and gets turgid
Hypertonic
Inside of cell has higher water potential than solution
Animal cell- cell shrivels and shrinks
Plant cell- cell shrinks and is plasmolysed
Water potential of pure water
0
What is a vaccine?
The introduction to the body a dead or attenuated pathogen which brings about an immune response preventing an individual contracting a disease.
Ways a vaccination is taken
May be injected or taken orally
Ethical issues of vaccinations
-Animal testing
-Animal based substances used
-Testing on humans potentially putting them at risk
-Benefits must outweigh financial cost
-People declining vaccine stopping protection of population
What is active immunity?
Stimulation of the production of antibodies by the individuls own immune system (direct contact with pathogen)
Types of active immunity
Natural- normal life processes (exposure to disease)
Artificial- medical intervention (vaccine)
What is passive immunity?
Introduction of anitbodies to individual from an outside source (no direct contact with pathogen)
Factors of active immunity
- Requires being exposed to antigen
- Slow response
- Memory cells produced
- Long term production
Factors of passive immunity
- No exposure to antigen required
- Immediate response
- No memory cells produced
- Short term protection
Meaning of herd immunity
When a large proportion of a population has been vaccinated making it difficult for a pathogen to spread - advantageous to those who havent got vaccine as it protects them not catching disease.
Reasons a vaccine may not eliminate a disease
- Individuals not getting vaccine for religious, medical or ethical reasons
- Multiple varieties of pathogen
- Antigenic variation as pathogen frequently mutates causing vaccine to be ineffective
- Individuals getting disease before or after vaccine as immunity levels arent high enough to prevent it
- Pathogens may ‘hide’ from immune system in cells or intestines
Side effects of cancer treatment
May disrupt cell cycle of normal cells as it cannot distinguish between the two
( more likely kill tumour cells as they have a much faster division rate)
Role of B cells
Create and secrete antibodies complementary to antigen.
Divide by mitosis to form plasma cells.
Produce memory cells for further antigen intrusion
Advantages of SEM
- Produce 3D images
- Can be used for thicker specimens as electrons dont pass through
- Can see surface of specimen
Limitations of SEM
- Low resolution images
- No living specimens used as prepared in a vacuum
What is added to microscope images to produce colour?
False colour imaging
Which polymer are antigens typically?
Typically proteins so are enourmously variable due to tertiary structure.
Blood groups recognition
A- a antigens
B- b antigens
AB- a and b antigens
o- neither antigens
How may you treat HIV?
Treating HIV is difficult because it is a virus.
HIV has some virus-specific enzymes (e.g. reverse transcriptase) and so antiviral drugs can be designed to target the reverse transcriptase enzyme
Binary fission
DNA replication
Cell growth
Cell division
What is binary fission
Type of asexual reproduction in prokaryotes
Temporary mounts
- Add a drop of water onto slide to keep specimen in place
- Place a thin specimen on water
- Add a drop of specific stain (highlight certain objects).
- Slowly add a cover slip, place upright next to slide and tilt it down onto specimen using a mounted needle to prevent artefacts
What are artefacts?
Things present on microscope which are not present on cell or specimen
- Air bubbles, fingertips, damage to specimen
(typically formed during prep)
Two types of elisa tests?
Direct- uses a single antibody complementary to antigen being tested for
Indirect- uses two different antibodies (primary and secondary)
Function of elisa tests
- uses antibodies to detect presence of proteins in a sample, as well as its quantity.
Lateral flow tests function
Used to detect the presence of hormones or antigens from a patient’s sample.
What does ELISA test stand for?
enzyme linked immunosorbant assay
Nucleus structure and function
- animal and plant cells
Double membraned (envelope) organelle which contains many pores for molecules to leave and enter. Has many chromatin and nucleolus for ribosome production.
Controls activity of the cell
Holds genetic material, linear DNA
Cell surface membrane
- animal and plants and bacteria cells
Controls substances entering and exiting cell. Has receptor molecules to respond to chemicals
Mitochondria
- animal and plant cells
The site of the cell’s energy production and other metabolic functions. Oval shaped with double membrane. Inner membrane is folded to form cristae with a liquid matrix inside to hold enzymes for respiration. Produces ATP.
Contains small, circular DNA
Golgi apparatus
- animal and plant cells
A group of fluid filled, membrane bound flattened sacs called cisternae. These process and package lipids and proteins which are transported out of cell by vesicles surrounding the edge. Also produce lysosomes.
Rough endoplasmic reticulum
- animal and plant cells
System of membranes that enclose a fluid filled space, covered in ribosomes as it folds and processes proteins
Smooth endoplasmic reticulum
- animal and plant cells
System of membranes that enclose a fluid filled space, it synthesises and processes lipids
Ribosomes
- animal and plant and bacterial cells
Can float around cytoplasm or be attached to the rough ER (in eukaryotes), surrounded by a membrane and site of protein synthesis.
In prokaryotes- 70S
In eukaryotes- 80S
Lysosomes
- animal and plant cells
Round organelles surrounded by a membrane with no clear internal structure, contain digestive enzymes called lysozymes which can break down/hydrolyse invading cells or worn down cell components. Separate from cytoplasm
Cytoplasm
- animal and plant and bacterial cells
All chemical reactions take place here
Chloroplast
- plant cells
Small flattened structures surrounded by a double membrane, found in photosynthetic organisms. Membranes called thylakoids can be stacked together to form grana, if two or more grana are joined together it is lamellae. Liquid found is stroma.
Chloroplast DNA is smaller, circular and not associated with histones
Contain chlorophyll
70S ribosomes
Cell wall
- plant and bacterial cells
Provides support for cell and prevents it changing shape
Plant and algal- cellulose
Fungal- chitin
Bacterial- murein
Vacuole
- plant cells
Membrane bound organelle found in cytoplasm of cell, tonoplast membrane. Contains cell sap to keep cell turgid maintaining its pressure. Involved in the isolation of unwanted chemicals in cell.
Circular DNA
- prokaryotic cells
Single coiled up strand not attached to any histone proteins.
Plasmids
- prokaryotic cells
Small loops of DNA separate from main circular DNA, contains genes that can be passed between prokaryotes (not present in all)
Slime capsule
- prokaryotic cells
Some prokaryotes contains this outer layer. Helps protect bacteria from drying out and being attacked by cells of immune system by host organisms.
Flagellum
- prokaryotic cells
Long hair-like structures that rotate enabling bacteria to move by the corkscrew shaped filament. Some have one, some have more than one.
Core
- viruses
Holds genetic material (DNA + RNA)
Capsid
- viruses
Protein coat which protects the viral genome from external environments. Some may have a lipid coat containing glycoprotein
Attachment proteins
- viruses
On surface of capsid allowing viruses to bind to complementary receptors on host cell
Virus replication
- use attachment proteins on capsid to bind to complementary receptors on host cells plasma membrane
- virus injects nucleic acid into cytoplasm (lysogenic cycle)
- host cell uses nucleic acid to produce new viral particles using reverse transcriptase to convert RNA into DNA
- host cell bursts through a lytic release releasing viral particles to other tissues and cells
Reasons prokaryotes differ from eukaryotes
- cytoplasm lacking membrane bound organelles
- structurally smaller ribosomes
- no nucleus but a single circular DNA free in the cytoplasm, not linked to proteins
- cell wall made of murein (glycoprotein)
