Cells Flashcards
Prokaryotic cell
- no nucleus
- no membrane bound organelles
- small 70s ribosomes
- circular DNA
- murein cell wall
Eukaryotic cells
- contains nucleus
- contains membrane bound organelles
- larg(er) 80s ribosomes
- linear DNA
- no murein in cell wall (if present)
Conditions for ultracentrifugation
Isotonic - prevents osmotic movement
Ice cold - prevents enzyme action
pH buffer - so proteins aren’t denatured
Order of cell density for ultracentrifugation
Nucleus - chloroplast - mitochondria - (S/R) endoplasmic reticulum - ribosomes
Ultracentrifugation method
Cells homogenised in a blender - to access organelles
Homogenate filtered to remove debris
Homogenate centrifuged at low speed
Densest organelles form pellet
Supernatant cannot bind be spun again
Transmission electron microscope
High(er) resolution
2D image
Internal structures are visible
Sections must be thin
Scanning electron microscope
Low(er) resolution
3D image
Internal structures not visible
Sections can be thick(er)
Electron vs. Light microscope
Greater resolution - lower resolution
Focused with magnets - focused with lenses
Specimen must be dead - specimens can be living
Image in b+w - image in colour
Phospholipid bilayer
Enables passage of lipid soluble molecules
Hydrophilic heads
Hydrophobic tails
Cholesterol - provides strength
Carrier protein - specific tertiary structure complimentary to polar molecules (facilitated diffusion + active transport
Channel protein - specific tertiary structure, size, and charge ( facilitated diffusion)
Nucleus
Contains genetic material
-bound by membrane
- controls protein synthesis
Ribosome
- used in protein synthesis
- very small
Made of protein and ribosomal RNA
Mitochondria
- involved in aerobic respiration
- bound by 2 membranes
- Cristae (folds of membrane)
- matrix contains enzymes, ribosomes, and DNA
Chloroplast
- only found in photosynthesising plant cells and algae
- bioconversion disk
- surrounded by 2 membranes
- large surface area for chlorophyll to absorb light
Endoplasmic Reticulum
Rough
- surface has ribosomes that produce protein
- protein releases and sent to Golgi apparatus for packaging
Smooth
- lacks ribosomes
- involved in lipid transport
Golgi apparatus / vesicle
- adds carbohydrates to proteins from REr
Forms glycoprotein - packages glycoprotein into Golgi vesicle for secretion
- produces lysosomes which release lysozyme (hydrolytic enzyme)
Lysosome
- digests materials taken by phagocytosis
- lysosome fuses with vesicle and release lysozyme
- engulfs and digests organelle
Ficks law
Rate of diffusion is proportional to
(Surface area x concentration difference) / diffusion distance
Facilitated diffusion
Movement of large polar molecules down a concentration gradient
Uses channel and carrier proteins
Passive - requires no energy
Active transport
Movement of molecules / ions through a partially permeable membrane by carrier proteins against a concentration gradient
Requires energy from ATP hydrolysis
Osmosis
Movement of water molecules from a high water potential to low water potential across a partially permeable membrane
Water potential
Potential of water to leave a solution by osmosis
How do viruses replicate?
-attach to host cells using glycoproteins which are complementary receptors on cell surface membranes
- inject nucleic acid into host cell
- codes for more virus particles
- produces copies of viral nucleic acid and proteins
- released by lysis of cell
HIV Replication
Host cell - helper T cell
- virus attaches using glycoprotein spike, complementary to receptors on T-cell
- lipid envelope fuses with cell membrane
-RNA, reverse transcriptase released into cell - viral DNA formed from viral RNA using reverse transcriptase released into
- viral DNA enters host nucleus
- host cell replicates viral DNA as well as own
- HIV particles assemble
- viral envelope forms
- host cell destroyed
Phagocytosis
-phagocyte engulfs pathogen
- forms phagosome
- lysosomes fuse with phagosome, lysozyme hydrolyses pathogen
- soluble product digested, insoluble product removed
Humoral response
- Body has b-lymphocytes with specific antibodies on cell surface membrane
- Antigen on pathogen attaches to complementary antibody
- Helper T cell activates B-cell
- B- cell stimulated to divide by mitosis
- Lots of identical plasma cells
- plasma cells produce antibody
Memory B - cell
Primary response takes up to 72 hours - symptoms arise
If same antigen encountered memory B-cells develop into plasma cells
Plasma seas secrete antibodies at greater concentration than primary response
Provides immunity
T- cells
Phagocytosis occurs
Phagocyte embeds antigen in its cell surface membrane - becomes antigen presenting
T- cells with complementary receptor binds to antigen
Helper t-cells divide by mitosis
What do t-cells divide into?
More helper t-cells
Memory t-cells
Or they activate cytotoxic t-cells - secrete chemical to destroy specific antigen
Passive immunity
Individual receives preformed antibodies from outside source
Not exposed to antigen
Provides short term immunity
Active immunity
Individual is exposed to antigen and produces antibodies
Immune system produces antibodies
Long term immunity provided
Example: natural passive immunity
Through placenta / breast milk
Example: artificial passive immunity
Preformed antibody is injected following exposure eg. To toxins
Example: natural active immunity
Individual exposed to antigen and is infected
Example: artificial active immunity
Individual is vaccinated
Direct Elisa
Plastic tray divided into wells - with specific monoclonal antibody
Sample is added to well - if antigen present it will bind
Second monoclonal antibody added with enzyme attached
Wash to remove unbound antibody
Add substrate for enzyme - if enzyme present colour product will form
Indirect Elisa
Specific antigen bound to well
Sample added if antibody is present it will bind
Second antibody is added - with enzyme attached
Wash to remove unbound antibodies
Substrate for enzyme added - intensity of colour proportional to enzyme concentration
