Eukaryotes Flashcards
Why is cell size limited in eukaryotes
SA/vol ratio
Diffusion rates of molecules (partly determined by particle size)
The need for high concentrations of compounds and enzymes for reactions
What is the use of compartmentalisation of eukaryotic cells
Compartmentalisation = processes localised and concentrated
Subdivide into membrane bound compartments (organelles)
Need for active and organised transport system (cell signalling, cytoskeleton etc)
Use of differentiated eukaryotic cells
Compartmentalisation = specialisation of specific tasks
Important for multicellular organisms
May have random mutation during development
stem cells in eukaryotes
Can become anything
Regulated by intra/extracellular signals (biotic and abiotic)
In both plants and animals
What are the 3 ways to study organelles
- drawings
- fluorescence microscopy (tag organelle with fluorescent protein)
- electron microscopy (fix cell and cut slices then stain with OsO4
Describe transport/secretory vesicles
Membrane bound
Contains proteins for transport/export
Only secretory if actually being secreted
Trafficked along cytoskeleton
Describe lysosomes
Storage for enzymes that break up cellular components
Contain at least 50 hydrologic enzymes
Can break down almost any biological molecule so must remain separated
Degradation of organelles via autophagy = organelles delivered to lysosomes for degradation
A lot of diseases related to misfunction of lysosomes
Describe peroxisomes
Assist lysosomes in cell clean up
Generate and degrade hydrogen peroxide
Breakdown fatty acids/lipid components of membranes
Detoxify harmful compounds
Describe centrosome
Very different between plants and animals
Important in cell division
Taxol (form of trees) important in cancer treatment: Causes binding of centrosomes and microtubules
Describe cytoskeleton
Frame work: shape and structure Forms basis of internal transport Cellular movement Contraction of skeletal muscle Made of microtubules, microfilaments, intermediate filaments and Actin
Describe microtubules
Monomers that polymerise
Very hard to see in electron microscope - if used fluorescence whole cell glows
Organised in bundles
Constantly built (polymerisation end) and broken down (depolymerisation end)
Describe actin
Influence locomotion and movement
Major cytoskeleton component of muscle cells
Describe nuclear pores
30 different proteins used to make a pore
- proteins made in cytosol
Outer diameter 120nm
Fusion of inner and outer membrane
Small particles injected into the cell can directly enter the nucleus: channels freely permeable to ions and small molecules
Describe proteins used for nucleus pores
Made in the cytosol
Contains NLS: nuclear localisation signal (specific amino acids sequence)
NLS recognised by receptor protein called importin they bind and regulate transport through pore
She’s ATP delivered by RAN-GTPase
Describe how RNA leaves the nucleus
Transported through a nuclear pore into cytosol
Binds to protein containing nuclear export signal (NES)
NES recognised by exportin receptor protein
Exportin transports them through the pore
Describe the nuclear matrix
Genetic information located there
Each chromosome has its own discrete location
Maintains shape of nucleus: made of insoluble network fibrous proteins Called Latins
- line the inner membrane
-provides mechanical strength
Newly synthesised nucleic acids associate with the matrix
Describe the nucleolus
Dedicated for ribosome production
1+ spherical structures, several micrometers in diameter
Number and size corresponds to level of protein synthesis
What are the functions of the smooth endoplasmic reticulum
Drug detoxification Carbohydrate metabolism -hepatocytes break down stored glycogen Calcium storage - sarcoplasmic reticulum in muscle cells -released in response to extracellular signalling fr muscle contraction Steroid biosynthesis - adrenal glands, testes, ovaries - cholesterol and steroid based hormones
What are the 3 types of endoplasmic reticulum
Rough
Smooth
Transitional (exit site of proteins leaving rough ER)
How do vesicles move along the cytoskeleton
Via active transport
Microtubules = long range transport
Actin = short range
Adaptor (attachment) and motor (walking) proteins use them to move along.
What are the 3 regions if the golgi
Cis
- contains golgi network and cis cisternae
- receives proteins from ER and acts as sorting station
Medial
-cisternae
Trans
- golgi network and trans cisternae
What are the 2 methods of how the Golgi body turn vesicles into secretory vesicles
Vesicular transport theory
Cisternal maturation theory
Describe vesicular transport theory
Vesicles enter from bottom to top (cis to trans)
Resident enzymes stay in cisternae
Proteins are moved between the cisternae
Describe cisternal maturation theory
Currently favoured theory
- cis cisternae mature into trans cisternae and new cis created from fusion of vesicles at cis face
Enzymes move from trans down to cis
How do golgi differ in plants from animals
Animals = few large Golgi localised around nucleus Plants = loads of small golgi
What is anterograde transport of vesicles
Forward pathway of vesicles for secretion
What is retrograde transport
Vesicles released in opposite direction
Vesicles fo back to endoplasmic reticulum and eventually the cytosol
Why do mitochondria have such elaborate structures?
- is the site of aerobic respiration
Glucose + oxygen = carbon dioxide and water (ATP synthesised)
Needed for the oxidation of glucose = proton gradient, pumps protons into intercellular space and drives ATP synthesis
Describe mitochondrial matrix
Contains enzymes, DNA and ribosomes and other enzymes encoded in the nucleus and imported
What does mitochondrial DNA code for
RRNA
TRNA
Inner membrane proteins
Describe mitochondrial Cristae
Used to increase SA (inner 5 : outer 1)
Can accommodate large number of protein complexes
Number of mitochondria and number of Cristae ~ activity of cells
Describe mitochondria inner membrane
Permeability barrier to most solutes
Partitions the mitochondria into 2 components: creates inter membrane space
Describe mitochondrial outermembrane
No significant permeability barrier
Contains trans membrane channel proteins called porins
Describe endocytosis
Imports extracellular material
Uses cell/tissue specific receptors localised in plasma membrane (isn’t passive)
Protein will be complementary = bind and form complex which creates coat proteins that make coat complex on inside of the cell
When complex made membrane will invaginate and create vesicle: inside is coated pit
Describe endosomes
Endocytic vesicles fuse to create early endosome then fuse again to create late endosome
During process PH decreases: due to degrading enzymes from golgi
Endosomes create lysosomes and vesicles produced by golgi contains lysosomal proteins then leave the cell via exocytosis
Transport material to golgi, lysosome or vacuole (plants)
Describe exosomes
Extracellular vesicles
Formed from cell membrane
Components enter from cytoplasm and binds back with membrane then releases components out of cell
Play large role in cell-cell signalling
What are the roles of microtubules
- Organisation of cell shape and polarity
- Intracellular transport of vesicles and organelles
- Chromosome movements
What are the microtubules subunits and how do they form microtubules
Alpha - tubulin
Beta - tubular
Together they form tubulin dimer
Tubulin dimers form Oligomers and then protofilaments
- sheet of protofilaments form a microtubule
How do microtubules grow
They exam and from the plus end and also break down from the plus end
Describe motor proteins
Kinesin = moves towards plus end
Dynein = moves towards the negative end
Energy dependent process
What are the subunits of microfilaments
Subunits = g-actin monomer
What are the functions of microfilaments
Cell locomotion Cytokinesis Muscle contraction Maintenance of cell shape Intracellular transport
Describe polymerisation of microfilaments
G actin builds up and creates filamentous actin (f actin)
Can become many different types of proteins
Describe depolymerisation of microfilaments
Depolymerises from the pointed end of the actin filaments Capping proteins bind to actin filaments = barbed end and prevents filament assembly Protrusion filpodium (protrusions created by actin bundles) prevented
Describe the movement of actin
Extension at the front
Adhesion
Translocation via contraction at the back
De-adhesion of back section
What are functions of intermediate filaments and its subunits
Subunit: dimers Functions: -structural support -maintenance of cell shape - nuclear lamina
How does the intermediate filament subunits build up
Becomes tetramer then protofilaments then filament
