3.2 Cells Flashcards
Nucleus structure
Nuclear envelope - double membrane
Nuclear pores
Nucleoplasm
Chromosomes - protein bound linear DNA
Nucleolus - site or rRNA production and makes ribosomes
Nucleus function
Site of DNA replication and transcription
Contains the genetic code for each cell
Endoplasmic reticulum structure and function
Folded membrane called cisternae
Rough ER has ribosomes on membrane
Rough ER - protein synthesis
Smooth ER - Synthesis and storage of lipids and carbohydrates
Golgi body function and structure
Folded membranes making cisternae
Vesicles surrounding it
Form glycoproteins
Produce secretory enzymes
Transport lipids
Form lysosomes
Finished products are transported to cell surface in vesicles where they fuse with the membrane and their contents are released
How do molecules move within a cell
Finished products are transported to cell surface in vesicles where they fuse with the membrane and their contents are released
Lysosomes structure and function
Bags of digestive enzymes
Hydrolyse phagocytic cells
Hydrolyse dead cells
Release enzymes
Digest worn out organelles
Mitochondria structure
Double membrane
Inner membrane - cristae
Fluid centre - matrix
Loop of mitochondrial DNA
Mitochondria function
Site of aerobic respiration
Produces ATP
DNA to code for respiration enzymes
Ribosomes structure and function
Site of photosynthesis
No membrane
2 sub units made up of protein and RNA
Different sizes in eukaryotic and prokaryotic
Vacuole structure and function
Fluid filled sac
Keeps cell turgid
Temporary stores of sugars and amino acids
Chloroplasts structure and function
Surrounded by a double membrane
Contains thylakoids
Fluid filled stroma contains enzymes for photosynthesis
Site of photosynthesis
What organelles have double membranes
Nucleus
Mitochondria
Chloroplast
Cell wall monomers
Plants - Cellulose
Bacteria - Murein
Fungi - Chitin
Cell wall function
Provide structural strength to cell
Plasma membrane function and structure
Controls entrance and exit of molecules into cells
Phospholipid bilayer
Prokaryotic vs Eukaryotic
Cells are much smaller
No membrane bound organelles
Smaller ribosomes
No nucleus
Murein cell wall
May contain: plasmids, flagella, slime capsule
What are viruses
Acellular, non living particles
Structure of a virus
Attachment proteins
Capsid
RNA/DNA
Viral envelope
Magnification definition
How many times larger an image is compared to the object
Resolution definition
The minimum distance between two objects in which they can still be viewed as separate
Why do electron microscopes have a better resolution that optical microscopes
Electrons have a shorter wavelength than light
Transmission electron microscope
Thin specimens placed in vacuum and have beam of electrons fired through. Some parts absorb more electrons and appear darker. 2D
Optical vs electron microscope
Optical uses light, electron uses electron
Poorer resolution due to light have a longer wavelength
Lower magnification
Colour images
Can view living samples (electron samples must be in a vacuum)
Scanning electron microscope
Specimen does not need to be thin. Electrons are beamed onto surface and scattered, giving 3D images
Cell fractionation steps
- Homogenisation - cells are broken open to release organelles using a blender
- Filter to remove large cell debris
- Placed in centrifuge and spun at low speed
- Densest organelle forms pellet at bottom
- Remove pellet and spin supernatant at a faster speed
- Repeat
Why must cells be prepared in a cold, isotonic and buffered solution
Cold - reduce enzyme activity which could damage organelles
Isotonic - prevent osmosis which could cause organelles to shrink/burst
Buffered - Prevent pH change which could damage organelles
What are G1 S G2 and M
G1 - Growth
S - DNA synthesis
G2 - Growth and preparation for mitosis
M - Mitosis
Stages of mitosis
- Prophase. Chromosomes condense and become visible. Centrioles move to opposite poles of cell
- Metaphase. Chromosomes line up along equator of cell. Spindle fibres attach to centromere
- Anaphase, spindle fibres shorten, causing the centromere to divide in two, so individual chromatids are moved to opposite poles. Requires ATP
- Telophase. Nuclear membrane reforms, cytoplasm splits in two to form two identical daughter cells
Binary fission steps
- Replication of circular DNA and of plasmids
- Division of cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of plasmids
Why is it called the fluid mosaic model
Fluid - Components can move along/across phospholipid bilayer
Mosaic - composed of many different molecules
Components of the plasma membrane
Phospholipid bilayer
Glycoproteins and glycoplipids (cell recognition)
Cholesterol
Channel and carrier proteins (integral proteins)
Peripheral proteins (mechanical support)
What types of molecules can diffuse through the phospholipid bilayer
Small lipid soluble molecules
What are the 5 types of transport
Simple diffusion
Osmosis
Active transport
Facilitated diffusion
Cotransport
Simple diffusion definition
Net movement of molecules from an area of higher concentration to an area of lower concentration. Passive.
Facilitated diffusion
Net movement of molecules from an area of higher concentration to an area of lower concentration using channel/carrier proteins. Passive.
Osmosis
The net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane.
Hypotonic
Water potential of a solution if more positive than the cell. TURGID.
Hypertonic
Water potential of a solution is more negative than the cell. FLACCID.
Active transport
Movement of substances from an area of lower concentration to an area of higher concentration using ATP and a CARRIER protein.
How does active transport across a membrane worj
- Molecule binds to a complimentary receptor.
- ATP binds to carrier protein from inside of cells and is hydrolysed to ADP and Pi
- Causes the carrier protein to change shape, releasing the molecule to the other side
- Phosphate ion is released, so carrier protein returns to original shape
Co-transport of glucose in ileum
- Sodium ions actively transported out of epithelial cell into blood
- reducing sodium concentration inside of cell
- Sodium ions diffuse into the cell from the lumen and are co-transported with glucose/amino acid
- Glucose then moves by facilitated diffusion into the blood.
Cell adaptations for transport
- Increase in surface area
- Increase in number of channel and carrier proteins in the membrane
What types of cells trigger an immune response
Pathogens
Foreign cells
Tumour cells
Toxins
Allergens
Antigen definition
Molecules (usually proteins) that trigger an immune response
Why is it hard for your body to fight off pathogens
A pathogens DNA can mutate frequently. If a mutation occurs in the gene which codes for a protein, then the shape of the antigen will change. This means any previous immunity to this antigen is no longer effective as memory cells will have memory of old antigen shape
Parts of the innate immune system
Physical barriers - skin
Chemical barriers - saliva, tears, stomach acid
Phagocytes
Phagocytosis
- Phagocyte receptors bind to antigens on pathogen
- Phagocyte engulfs pathogen, forming a phagosome
- Lysosomes fuse with phagosome and release hydrolytic enzymes, destroying the pathogen
- Pathogen antigens are modified and displayed on phagocyte cell surface membrane
Where are lymphocytes formed
Bone marrow
T cells
- Helper T cell binds to pathogen antigens on phagocyte
- Stimulates T cell to divide by mitosis, forming many clones
- Clone helper T cells differentiate into Helper T cells, memory cells or cytotoxic T cells
Cytotoxic T cells
Release perforin which makes holes in cell surface membrane if pathogens. Cell may burst or shrink and die.
B cells
1.Helper T cells bind to complimentary B cell receptor
2. Stimulates B cell
3. B cell divides by mitosis into plasma cells which are clones
4. Plasma cells release antibodies complimentary to antigen
5. Some plasma cells remain as memory cells
6. Antibodies attach to pathogen and destroy them
Antibody definition
Quaternary protein released by plasma cells in response to antigens. They can agglutinate pathogens.
Antibody structure
Quaternary proteins - 4 polypeptide chain
Variable region - antigen binding sites
Constant region
Heavy and light chains
2 variable regions so can bind to two antigens, clumping pathogens together - agglutination
Memory B cells
Will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered
Primary vs secondary response
Primary response is much slower as it needs time to identify, select and clone the specific lymphocytes needed. Primary response is also less strong. Secondary response involves memory cells.
Active vs Passive immunity
- Active involves formation of memory cells, passive doesn’t
- Active involves production of antibodies by plasma cells in response to antigen
- Passive involves introduction of antibodies from outside the body
- Active long term as antibodies produced in response to antigen
- Passive short term as introduced antibodies are broken down
- Active can take a while for effects, passive is rapid
Active artificial and natural examples
Artificial - Vaccination
Natural - Normal body response to antigen
Passive artificial and natural examples
Artificial - Antibodies from mother through placenta
Natural - Antitoxin for snake bite
Vaccine definition
When small amounts of weakened or dead pathogen or antigens are introduced into the body
Vaccine process
- Antigen/pathogen introduced
- Exposure to antigen activates B cells to go into clonal expansion and differentiation
- B cells undergo mitosis and make clones of plasma cells, which release antibodies
- Some plasma cells remain in the blood as memory cells
- Next time antigens are present, memory b cells produced antibodies rapidly, so no/few symptoms
Herd immunity definition
If enough of the population are vaccinated, the pathogen cannot spread easily amongst the population, providing protection for people who cannot take vaccines.
HIV structure
Genetic material
Reverse transcriptase enzyme
Capsid
Envelope
Attachment proteins (CD4)
HIV replication
- HIV attachment proteins bind to CD4 receptors on helper T cell
- HIV RNA injected into cell alongside enzymes
- Reverse transcriptase converts viral RNA to DNA
- Integrase inserts viral DNA into cellular DNA
- Viral proteins produced
- Viral particles assembled and released
What does AIDS do
Interferes with the normal functioning of the immune system. T helper cells are destroyed, leaving the person vulnerable to infections and cancer. It is this that leads to death rather than HIV directly.
Monoclonal antibody definition
A specific type of antibody produced by a single clone of B cells, that binds to only one specific antigen. They are proteins with binding sites with complimentary shapes to antigens.
Uses of monoclonal antibodies
Medical treatment
Medical diagnosis
Pregnancy tests
Direct monoclonal antibody therapy
- Monoclonal antibodies are produced with a binding site complimentary to antigen of cancer cell
- Antibodies given to patient and attach to cancer cells
- Prevents chemicals binding to cancer cells that could cause uncontrolled cell division
- So prevent cancers growing
Indirect monoclonal antibody therapy
- Monoclonal antibodies are produced with a binding site complimentary to antigen of cancer cell, but also have a drug/fluorescent dye attached
- Cancer drugs are delivered directly to the cancer and kill them
- Reducing side effects from conventional methods
- or cancer is highlighted for surgery/after surgery
ELISA test
- Fix antigen to bottom of beaker
- Add complimentary antibody (WASH)
- Add 2nd antibody which has an enzyme attached (WASH)
- Add substrate complimentary to enzyme (WASH)
- Depth of colour change indicates positive result
Ethical issues of monoclonal antibodies
-ves
Use of animals in production
+ves
Better treatment of cancers in humans
Detection of disease
