Cell structure

Question 1

Describe the lipid bilayer and its proteins.

Answer 1

It is amphipathic - with hydrophilic groups on the exterior and hydrophobic group are positioned on the interior of the bilayer.

Lipids and sterols are asymmetrically distributed. Cell membranes are fluid structures so many proteins and lipids can move laterally.

Most proteins are glycosylated. 
There are two classes of proteins 
1. Integral membrane proteins: the will cross the entire width of the cell membrane and have three domains 
    A. cytoplasmic
    B: membrane spanning 
    C: external 

2. Peripheral membrane proteins: are attached to the cytoplasmic/extracellular regions of the lipid bilayer non-convalently

There are more proteins associated with the cytoplasmic face because proteins are stabilized by the cytoplasm.

Question 2

Describe normal RBC and Hereditary spherocytosis

Answer 2

The biconcave shape of RBCs is a result of proteins on the inner surface of the RBC interact with cytoskeleton proteins (spectrin).

Hereditary spherocytosis is a results of absence of spectrin, RBCs are more spherical in shape and more senstive to mild hypertonic solutions (shrivels)

Question 3

What are four functions of membrane proteins?

Answer 3

1. link or anchor molecules that interact with intracellular cytoskeletal proteins like spectrin
2. Serve as transporters for bilateral movement in and out of the cell
3. Receptors (bind ligand and signal shit)
4. Sometimes enzymes.

Question 4

Describe small intestine epithelium

Answer 4

The tissue is mostly tall columnar cells (enterocytes) with modification at their surface. The apical/luminal surface features the brush border and microvilli

Microvilli extend (actin filaments) from the apical surface and increase absorptive surface. On the opposite end, they terminate at a filamentous complex, terminal web (actin + intermediate filament)

On top of that is a glyocalyx, (containing enzymes involved in the terminal stages of protein and carbohydrate digestion)
The include glycolipids, glycoproteins and proteoglycans.

also goblet cells that secrete mucous.

Lastly, cells interact on their lateral borders forming a tight junctional complex. They show up as red dots on a light microscope called terminal bars.

The lateral contact comes in the form of four kinds kinds. (from apical to down)

1. Tight/occluding junctions (zonula occludens)
2. belt desmosomes (zonula adherens)
3. spot desomsomes (macula adherens
4. Gap junctions

Question 5

Describe the cytoskeleton

Answer 5

Actin: bundles of microfilaments, they will interact with myosin.

Microtubules: bundle of tubulin. 9 + 2 array of the cilia and 9 triplets in the centriole.

Question 6

Smooth ER vs Rough ER>

Answer 6

Smooth ER has no ribosomes, lipid and steroid biosynthesis and detoxification of harmful substances, metabolism of a variety of drugs, and calcium ion storage.

Rough ER, contiguous with the nuclear envelope and secretory pathway. Proteins synthesized in Rough ER go to golgi complex.

Question 7

Describe the golgi complex

Answer 7

This cis Golgi network is closest to the rough ER the trans has vesicles budding from it. In between are cis, medial and trans cisterna.

Transport is usually done through vesicles.

Vesicles with lysosomal proteins and enzymes come from the Trans golgi network but remain in the cell.

Question 8

Difference between Constitutive secretion and regulated secretion.

Answer 8

Constitutive - continual secretion of proteins that are not store, few secretory granules

Regulated secretion - initiated by an external stimulus, leading to accumulation of many secretory cells.

Question 9

Describe endocytosis

Answer 9

Receptors (integral membrane proteins) bind ligands. The receptor ligand complexes then enter the cell by vesicle formation which is initiated by coat proteins binding to cytoplasmic lipid side.

This forms a coated pit which rapidly detaches from the surface to form a coated vesicle.

The internalized vesicles then fuse with the early endosome

Endosomes are organelles consisting of vesicles containing molecules that have entered the cell. Receptors and ligands are usually separated and receptors are recycled to the surface.

Question 10

Describe mitochondria

Answer 10

They are flexible structure that can change their shape and move throughout the cytoplasm.

The inner layer of the membrane is folded into cristae. On this membrane are spherical protein which couple oxidation to phosphorylation and ATP synthesis.

The number of mitochondrial cristae vary in different cells depending on energy needs.

Renal mitochondria contain unusual tubular cristae.

Question 11

Describe lysosomes and their identification.

Answer 11

Membrane bound packets of hydrolytic enzymes that are active at acid pH, site of intracellular digestion.

ATP driven proton pump maintains the pH.

Lysosomes degrade certain molecules that enter the cell.

They also digest worn out intracellular organelles and entire cells after phagocytosis.

You use trypan blue which is unable to be digested by lysosomes.
Or special lysosomes of eosinophils (cells that fight parasitic infections) have crystalline inclusions (like a line running through the middle)