3 - Eukaryotic cells Flashcards
Endomembrane system
A network of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.
Why are eukaryotic cells larger than prokaryotic cells?
Because of their internal membrane system.
How is genetic material organised in eukaryotic cells?
Chromosomes enclosed in a nuclear envelope
How is genetic material organised in eukaryotic cells?
Chromosomes enclosed in a nuclear envelope
What do plant cells have that animal cells do not?
Chloroplasts, central vacuole/tonoplast, plasmodesmata and a cell wall.
What do chloroplasts do?
Capture light energy and convert it into chemical energy
Where does photosynthesis occur?
In the stacks of thylakoid sacs (grana)
What do vacuoles do?
Store various chemicals and play a role in cell growth
What does the plant cell wall do?
Maintains cell shape and prevents mechanical damage.
What is the plant cell wall composed of?
Cellulose fibres embedded in a protein/polysaccharide matrix consisting of hemicellulose and pectin
What do animal cells have that plant cells do not?
Lysosomes, centrioles and flagella (in some plant sperm)
What do animal cells have that plant cells do not?
Lysosomes, centrioles and flagella (in some plant sperm)
What is contained in the nucleus?
Chromatin, nucleolus and nuclear envelope
What is contained in the nucleus?
Chromatin, nucleolus and nuclear envelope
What is contained in the cytoskeleton?
Microfilaments, intermediate filaments and microtubules
Which is the largest organelle in the eukaryotic cell?
Nucleus
What does the nucleus do?
Contains most of the genes which control the cell, some are present in mitochondria and chloroplasts.
What does the nucleus do?
Contains most of the genes which control the cell, some are present in mitochondria and chloroplasts.
What does the nuclear membrane do?
Encloses nucleus and separates it from the cytoplasm
Nuclear membrane
A double membrane containing nuclear pores (100nm in diameter)
What happens to chromatin during cell division?
Condenses into chromosomes
Where is mRNA synthesised?
Inside the nucleus from a DNA template
What happens to mRNA after it is synthesised?
Released into the cytoplasm via nuclear pores.
What does the plasma membrane do?
- Defines and contains the cell
- Controls entry of nutrients and exit of waste products.
- Maintains electrolyte balance
- Acts as sensor to external signals
Plasma membranes
Assemblies of lipids and protein molecules held together by non covalent interactions. Fluid mosaic model.
What is the purpose of the lipid bilayer?
Provides the basic structure of the membrane and serves as an impermeable barrier to most water-soluble molecules
Where are the protein molecules in the plasma membrane?
Dissolved in the lipid bilayer.
What will lipid molecules form in an aqueous environment?
Either micelles or bilayers
Three major types of lipids in cell membranes
Phospholipids, cholesterol and glycolipids
Three major types of lipids in cell membranes
Phospholipids, cholesterol and glycolipids
How is the lipid membrane a 2D fluid?
Individual lipid molecules able to freely diffuse within lipid bilayers but rarely move from one side to the other.
How do lipid molecules in the bilayer often move?
- Exchange places adjacently
- Rotate rapidly about their axis
What does the fluidity of a membrane depend on?
It’s lipid composition
What does a high level of cholesterol do to membrane stability?
Increases it by interacting with phospholipid molecules
How does the effects of cholesterol change at different temperatures?
Warm: Restrains movement of phospholipids
Cool: Maintains fluidity by preventing tight packing.
Transmembrane proteins
Where the polypeptide chain of membrane proteins crosses the lipid bilayer several times. Amphipathic.
How are peripheral membrane proteins associated with the membrane?
By non covalent linkages but are easily dislodged.
How can the shape and distribution of membrane proteins be observed?
Freeze fracture electron microscopy
How can the shape and distribution of membrane proteins be observed?
Freeze fracture electron microscopy
Freeze fracture
Specialised preparation technique that splits a membrane along the middle of the bilayer.
Freeze fracture
Specialised preparation technique that splits a membrane along the middle of the bilayer.
Functions of membrane proteins
- ) Transport proteins
- ) Receptor sites
- ) Structural
- ) Cell junctions
How do membrane proteins act as receptor sites?
The exterior region of a transmembrane protein may act as a receptor for a chemical messenger such as a hormone.
How do membrane proteins play a structural role?
Integrins allow the cell to attach to the extracellular matrix
How do membrane proteins play a role at cell junctions?
Separate apical and basal membranes which have different functions at tight junctions.
Cystic Fibrosis
An autosomal recessive disease that’s caused by a defective chloride ion channel.
What does the failure of the chloride channel result in?
A build up of viscous mucus within the lungs, making the individual prone to infections.
Where is a glycocalyx (thin layer of carbohydrate) present?
On the outside of the plasma membrane of most cells.
What are cell surface carbohydrates important for?
Cell-cell and cell-ECM recognition
How are carbohydrates important in blood types?
The ABO types are determined by carbs on the surface of RBCs
How are carbohydrates important in blood types?
The ABO types are determined by carbs on the surface of RBCs
What are membrane glycoproteins involved in?
Infection mechanisms
What must HIV do in order to infect a cell?
Must bind to the immune cell surface protein CD4 and a “co-receptor” CCR5
What cells can HIV not enter?
Resistant individuals that lack normal CCR5.
Endocytosis
The process where cells take in materials
Endocytosis
The process where cells take in materials
Pinocytosis
Cells infold parts of their plasma membrane to take up extracellular fluid in small vesicles. Non specific.
Phagocytosis
Uptake of insoluble material and a form of feeding in protozoa
What does receptor mediated endocytosis involve?
Binding of macromolecules to specific cell surface receptors which trigger endocytosis.
What does receptor mediated endocytosis involve?
Binding of macromolecules to specific cell surface receptors which trigger endocytosis.
What happens to macromolecules after endocytosis is triggered?
They become concentrated in endocytic pits.
What are endocytic pits coated with?
Clathrin, a bristle like protein
What does clathrin do?
Polymerises around the vesicle forming a cage like structure.
Exocytosis
The process of material being exported from the cell.
What does exocytosis involve?
Fusion of vesicles from the interior of the cell with the plasma membrane, the contexts then expelled into surrounding medium.
Why is exocytosis important?
Secretion of numerous proteins e.g. hormones and extracellular structural proteins and fluids.
How is receptor-mediated endocytosis used to deliver drugs into cells?
Drug is encapsulated in a liposome and the surface of the liposome has a peptide which binds to a cell surface receptor, triggering uptake of the liposome and drug into the cell.
