Unit 1 - Foundations of Cell Biology

Prokaryotes

Have no intracellular membranes and simpler structures

Eukaryotes

Have a nucleus and complex membrane bound organelles

1674

Leeuwenhoek sees the first living cell in a microscope

Cell Theory

Created in 1838 by Schwann and Schleiden statins cells are distinct, fundamental unit that creates organisms that occur spontaneously

Modern Cell Theory

All livign things are made of functional units (cells) that have hereditary information and comes from pre-exisitng cells via division with the same chemical composition and all nrg flow happens in cells

1951

George Gey establishes HeLa cells

1981

Transgenic mice and fruit flies

1995

Tsien GFP used for tagging

1998

Mice cloned from somatic cell via dedifferentiation

1999

Hamilton and Baulcombe discover siRNA

2006

Induced pluripotent stem cells

2009

Single cell sequencing to see transcriptome

2021

CRISPR

How thick are cell membranes?

10nm

What are Fatty Acids Made of?

COOH with even number of carbon tails

What is a Phospholipid made of?

Two fatty acids + PO₄ + glycerol backbone

1899 - 1925

Garter + Grendel proposed lipid bilayers

1935-1959

Unit membrane hypothesis describes the 3 layer membrae with proteins coating the lipid bilayers

1970s

Singer and Nicolson creates fluid mosaic model

What are Sphingolipids made of?

Sphingosine backbone + fatty acid + polar head group

What is a typical cell membrane made of?

Phosphoglycerides + sphingolipids + sterols

What are Phosphoglycerides made of?

Fatty acids + glycerol + phosphate + variable head group

Pure Sphingomyelin (SM) Bilayer

Thicker than phosphoglyceride bilayer and cholsterol lipid ordering increases its thickness

Phosphatidylcholine (PC) Bilayer

Flat monolayers of glycerol + choline + phosphate + fatty acids

What is Phosphatidylethanolamine (PE) made of?

Glycerol + phosphate + fatty acids + ethanolamine to form curved monolayer from its smaller head group

Cardiolipin

Only present in mitochondria membrane

What are ceramides made of?

Sphingosine + fatty acids

How does the inner layer fluidity compare to eternal?

More fluid with increased unsaturated bonds than outer

Flippases

P4-ATPase that translocates lipids to inner layer

Floppases

ABC transporters that move lipids to outer layer

Scramblases

Proteins that let lipids move in either direction

Presence of phosphatidylserine on the outer layer causes what?

Phagocytic signalling

Interdigitation

Acyl chain from a layer, protrudes into other layer

Membrane protein placement is determined by

Protein properties and it’ll mimick the fluidity of the layer

Prenylation

Lipid molecule attaches to a protein to help it stick to membrane

Glycosylphosphatidylinostiol (GPI)

Lipid anchor

Familiar Hypercholesterolemia

Mutation in LDL receptor genes causes increased cholesterol levels, resulting in premature cardio disease

Tay-Sachs Disease

Fatal genetic disorder from accumulation of gangliosides in brain cells via mutation in HEXA gene, affecting lipid metabolism

Plasmalogens

A special type of phospholipid in the heart and brain containing 1 ether link between the fatty acid and glycerol

The inside of a vesicle is equivalent to the

Extracellular layer of the cell

What does the RER do?

Synthesizes glycoproteins

What does the SER do?

Synthesizes lipids, and carbohydrates

Dolichol Phosphate

Hydrophobic 75-95 carbon lipid embedded in the ER that helps make oligosaccharides

Synthesis of Oligosaccharides

1. Dolichol phosphate attaches N-acetylglucosamine in cytosol

2. After mannose molecules are attached, dolichol flips into ER lumen

3. Finishes w/mannose and glucose molecules flipping to add

Adding and Processing N linked Oligosaccharides

1. Glc₃Man₉(GlcNAc)₂ precursor moves from dolichol to Asp tripeptide as it enters ER

2. Glucosidase I and II cleaves 2 glucoses

3. Calnexin/calreticulum grabs onto remaing glucose to help fold

4. Glucosidase II removes the last glucose

5. UGGT Glucose can be readded to help with folding

Protein Folding and Assembly

1. BiP binds to protein

2. Calnexin and calreticulin binds to olgosaccharide areas

3. PDI catalyzes disulfide bonds

What happens when a protein is misfolded?

ER mannosidase removes mannoases and OS-9 recoognzes it, signalling for degradation

Membrane Contact Sites

Tethered areas between organelles for moving lipids, Ca, trafficking and coordinate division

Membrane Contact Site Characteristics

No ribosomes and many contact points

How big is the gap between ER and endosome MCS?

3-15nm

How big is the gap between ER and mitochondria MCS?

6-15nm

What percentage do MCS cover mitochrondria and endosome SA?

2-5% and 3-5%

ORP1L

Cholesterol sensor on late endosomes that regulate endosome positioning

What happens to endosome in high cholesterol?

1. Rab7 recruits ORP1L and RILP

2. Cholesterol binds to ORP1L to bury FFAT motif

3. Buried motif stop VAP from binding

4. RILP binds to p150 subunit

5. Cholesterol levels causes complex to pack together causing motors to aggregate and walk

What happens to an endosome in the perphery in low cholesterol?

No cholesterol exposes ORP1L FFAT motif, causing VAP to bind to ER stopping moving

Protrudin

Adaptor molecule that regulates ER morphology and vesicular trafficking

Hereditary Spastic Paraplegia (HSP)

Mutation in protrudin

How do endosomes more outwards?

1. Rab7 and Ptdlins create a landing pad

2. Protrudin grabs onto Ptdlns-Rab7

3. FYOC1 on Rab7 interacts with protrudin to take the kinesin-1

4. Motor is activated and walks

Specialized Lipid Proteins (LTP)

Extract lipids, shield, bridge membranes and insert lipids

What are the specialized lipid proteins?

• ORP family

• START domain family

• SMP/TULIP superfamily

What happens to phosphatidylserine as it moves from ER to the mitochondria?

Becomes phosphatidylethanolamine

What happens to phosphatidylethanolamine as it moves from mitochondria to ER

Becomes phosphatidylcholine

STARD3

Moves cholesterol within the cell and facilitate membrane tethering

NPC1 & ORP5

Facilitates cholesterol from endosome to ER

Process of cholesterol moving from endosome to ER

1. ORP1L sense cholesterol and associated with VAP

2. STARD3 aids positioning

3. NPC2 brings cholesterol to NPC1

4. NPC1 passes cholesterol to ORP5

5. ORP5 inserts cholesterol into membrane

Concentation of Ca in ER

60 - 500um

Concentration of Cytosol

100um

Mitochondrial Ca Uniporters (MCU)

Specialized inner mitochondria channel for Ca

Voltage Dependent Anion Channels (VDACs)

Outer mitochondria channel that’s controlled by mitochondria via charge

Inositol

ER Ca channel

GRP78/BiP

Couples inositol and VDACs to enchance Ca moving

Uses of Ca

• Activates TCA dehydrogenases

• Signalling between ER and endosomes

• Regulates apoptosis

Endosome

Vesicle that sorts materials entering cell

How does ER help mitochondria fission?

1. ER wraps around fission sites

2. INF2 recruits actin-myosin

3. DRP1 aids fission

How does ER help endosome fission?

1. ER wraps around endosome base

2. FAM21 facilitates budding and helps recruit fission machinery

MFN2-MFN2/MFN1-MFN2

Helps with Ca transfer at contact sites

ORP1l-VAP

Senses sterol levels and regulates endosome positioning

Protrudin-VAP-Kinesin-1

Regulates endosome positioning via transfer

EGPR-PTP1B

Directs vesicle for recycling or degradation