Lecture 4 Flashcards
What type of cells contain several types of plastid? And an example?
Plant cells.
Chloroplasts.
What is the main function of the chloroplast, and where does this largely take place within?
Photosynthesis - occurs in stacks of thylakoid sacs, grana.
What do vacuoles in plant cells do?
Store various chemicals and aid cell growth.
What does the plant cell wall do?
Maintains cell shape. Prevents mechanical damage.
What is the plant cell wall composed of?
Cellulose fibres embedded in protein/polysaccharide matrix of mainly hemicellulose and pectin.
What is the largest organelle?
Nucleus.
What does the nucleus contain?
Also, what does the nuclear membrane do?
Contains most of the genes that control the cell.
Nuclear membrane encloses nucleus separating it from the cytoplasm.
How big is are nuclear pores in the membrane, and is it a single membrane?
100nm.
No, double.
What is contained within the nucleus?
Genes controlling the cell as DNA, organised into chromatin (along with histones).
Where are other genes that control small parts of the cell found?
Mitochondria, chloroplasts.
Where are the components of ribosomes manufactured?
Nucleolus.
Where is mRNA synthesised, and from what?
Where is it then released, to control what?
Inside the nucleus from DNA template.
Released into cytoplasm via nuclear pores, where it controls protein synthesis.
What does the Plasma membrane do?
Defines and contains the cell separating it fro its external environment.
Controls entry of nutrients and exit of waste products.
Maintains electrolyte balance in cell.
Acts as sensor to external signals.
What are plasma membranes?
Assemblies of lipids and protein molecules held together by mainly non-covalent interactions.
What model describes the way the plasma membrane is held together?
Fluid-mosaic model.
2 functions of the lipid bilayer?
Provides basic structure of the membrane.
Impermeable barrier to most water-soluble molecules.
Where are protein molecules found in the plasma membrane? What do they generally do?
Dissolved in lipid bilayer.
Carry out most specialised functions of the membrane.
What word describes membrane lipids’ ability to spontaneously form bilayers or micelles in an aqueous environment?
Amphipathic.
Can the lipid bilayer repair itself?
Yes.
What constitutes roughly half the mass of biological membranes?
Lipids.
3 types of lipids in cell membranes?
Which is the most common?
Phospholipids, cholesterol, glycolipids.
Phospholipids most common.
What is the structure of a phospholipid?
Polar hydrophilic head, two hydrophobic carbon tails.
Do lipid molecules move from one side of the membrane to the other?
Do they exchange places with adjacent lipid molecules?
Do they rotate rapidly about their axis?
Rarely.
Yes. 100,000 times/sec.
Yes.
Can lipid molecules diffuse within lipid bilayers?
Yes.
What does the fluidity of a membrane depend on?
What increases membrane stability? How?
Lipid composition.
High level of cholesterol, by interacting with phospholipid molecules.
What type of molecule is cholesterol? And what effect does it have in warm and cool temperatures?
Steroid.
Warm e.g. 37ºC - cholesterol restrains movement of phospholipids.
What is the name for a polypeptide chain of membrane proteins that often crosses the lipid bilayer several times?
Trans-membrane protein.
Are transmembrane proteins amphipathic? What does this mean?
Yes.
Hydrophobic and hydrophilic regions.
How are peripheral membrane proteins associated with the membrane? Are they easily dislodged?
Non-covalent linkages.
Easily dislodged.
How can the shape and distribution of membrane proteins be examined?
Also, can they move?
Freeze fracture electron microscopy.
Yes.
What do freeze-fracture studies support? And how does it work?
Support studies of the fluid mosaic model.
Splits membrane along middle of phospholipid bilayer.
4 functional types of plasma membrane proteins?
Transport proteins.
Receptor sites.
Structural roles.
Cell junctions.
What is cystic fibrosis, and what is it caused by?
Chronic disease causing buildup of viscous mucus within the lungs, making individual prone to diseases.
Caused by genetics (autosomal recessive), coding for defective chloride ion channel.
Are oligosaccharides and polysaccharides found on the surface of all eukaryotes? If so, what are they bound to?
Yes.
Bound to membrane proteins and lipids (glycolipids).
Are carbohydrates generally found on the inner or outer surface of the PM?
Outer.
What is present on the outside of the PM of most cells?
Glycocalyx.
What are known to be important in cell-cell and cell to extracellular matrix recognition?
Cell surface carbohydrates.
What are ABO blood types determined by?
Carbohydrates on surface of RBC.
What cell surface carbohydrates are involved in a common strain of HIV?
CD4 and CCR5.
How do cells take in materials? What are the 2 types?
Endocytosis.
Pinocytosis: cells infold small parts of Plasma membrane, taking up extracellular fluid in small vesicles - non specific.
Phagocytosis: uptake of insoluble material - form of feeding in protozoa.
What does receptor mediated endocytosis involve?
Binding of macromolecules to specific cell surface receptors, triggering endocytosis.
What are endocytic pits coated with?
What does this do?
Clathrin.
Polymerises round the vesicle, forming cage like structure.
When does exocytosis occur, and how does it work?
When material is ejected from the cell.
Vesicles fuse with plasma membrane, expelling contents into surrounding medium.
What types of proteins and fluid is exocytosis important in the secretion of?
Hormones, collagen.
Mucus.
