trial 1

What is the function of the smooth endoplasmic reticulum?

Lipid Synthesis

Detoxification of the liver

Calcium storage for thr muscles

Function of the nucleus in a cell?

It is the site of DNA replication, repair and ribosome assembly

Function of the rough endoplasmic reticulum

For the synthesis of proteins:

They are secreted from the cell

Then incorporated into the plasma membrane

Then they are transported to a different organelle for protein modification/glycosylation

Function of the golgi apparatus

Further processing of secreted proteins

Sorts proteins and directs localisation

The vesicles allow for communication (cis to trans)

Lysosome formation

What are vacuoles and what is their function

Found in animal and plant cells (more in plant)

Used for storage, fluid nutrients and waste products

What are the components of the endomembrane system

Nuclear envelope

Smooth and rough endoplasmic reticulum

Golgi apparatus

Transport vesicle

Lysosomes

Vacuoles

What is the mitochondria and what is its function

Double membrane bound organelle

It has the most eukaryotic cells

Generates energy by creating ATP (source of chemical energy)

Very small organelle and cannot be seen unless stained and it has its own DNA similar to bacterial genome

Functions of the membrane

Protects the cell

Controls movement of molecules

Transmits signals

Permits cell recognition

Compartmentalise cell (stays organised)

Allow cell/organelle motility

Performs reaction

Communicates with the surrounding cell

What are perixisomes

Cellular detox stations in the liver and kidney that break down fats and neutralise toxins to protect the cell from oxidative damage

2H2O2 (Hydrogen peroxide) -> 2H2O (water) + O2 (oxygen)

Structure of the membrane

Phospholipid bilayer with amphipathic molecules (hydrophobic and hydrophilic)

Hydrophobic head (Choline, Serine)

Hydrophobic fatty acid tail

Phosphate and glycerol group between head and tail

What are lysosomes and how do they digest material

They are membrane sacs that contain digestive enzymes (hydrolases) and they digest material by:

Phagocytosis (bacteria) - engulfs solid

Endocytosis (receptor bound substance) - takes in external materials

Autophagy (recycling materials) - digest its own internal parts

The nucleus and disease

Genetic mutations can activate oncogenes which causes uncontrolled division of cancer cells and this disabled tumour suppressor genes which leads to a loss of growth control

Drugs can target cell cycle checkpoints to stop tumour growth

Mitochondria and anti cancer drugs

This can be a drug target.

Doxorubicin can be delivered to mitochondrial DNA to increase drug effectiveness and reduce resistance

Golgi apparatus and neurodegenerative disease

Fragmentation/disintegration of the golgi is linked to alzheimer's and parkinson's.

Alzheimer's: Caused by Beta amyloid peptides activating enzymes that modify golgi structural proteins in the neurons

Parkinson's: Golgi disintegration involving proteins that are important for membrane transport

Lysosomal storage diseases

This occurs if enzymes are defective or missing which lead to a build up of molecules in lysosome that will kill it.

Example: Pompe disease (autosomal recessive disease) that leads to insufficient alpha-glucosidase (GAA) (that are responsible for degrading glycogen) causes skeletal muscle destruction and myopathy (muscles become weak)

Perixisomal and Lysosomal disorders

Lysosomes and Perixisomes play roles in waste break down and detoxification

Inherited errors in metabolism can involve complex molecule build up. This can damage cells in the brain, liver and muscles and can cause severe perixosome biogenesis disorders can severe lysosomal storage disorders

Targeting tumours and cancer cells

Liposomal drug formulations are used clinically for chemotherapeutic agents like doxorubicin and cytarabine.

This can treat cancers like ovarian, Aids related Kaposis's sarcoma, multiple myeloma, lymphomas.

Ongoing trials explore new liposomal drug combinations for improved targeting and reduced side effects

Effect of double bonds and degree of saturated/unsaturated fatty acids

Saturated fatty acids have no double bonds (straight tails- stronger intermolecular forces) so they pack tightly which means it reduces fluidity and makes membrane rigid

Unsaturated fatty acids contain one or more double bonds that create kinks in the tails (shorter tail, weaker for intermolecular forces) and these prevent tight packing and increase membrane fluidity

Real cells have a mix for balance

Effect of membrane cholesterol

Cholesterol molecules in the membrane acts as a temperature buffer

In cold temps the cholesterol keeps phospholipids apart which increases membrane fluidity

In warm temps cholesterol binds the lipids tighter together and decreases membrane fluidity

Function of membrane proteins (JETRAT)

Junctions - serve to connect and join two molecules together

Enzymes - Fixing to membranes localises metabolic pathways

Transport - Responsible for facilitated diffusion and active transport

Recognition- May function as markers for cellular identification

Anchorage - Attachment points for the cytoskeleton/extraceular matrix

Transduction - Functions as receptors for peptide hormones

Membrane permeability

Membranes are not very permeable towards: Large molecules, small molecules that are polar and/or charged

This can contribute to antibiotic resistance in bacteria, limit drug uptake into human cells

Lipophallic (fat-soluble) drugs can pass through the membranes easier

3 Classes of lipids: Phosphoglycerides (Phosphatidylcholine)

Most common membrane lipid

Structure: Glycerol backbone with two fatty acid tails - phosphate group + head group (choline) -> polar hydrophilic head

Amphipathic and forms main structure of the phospholipid bilayer

3 glycerol hydroxyl groups attach head to tail

3 classes of lipids: Sphimgolipids (sphingomyelin)

Less abundant

Structure: Built on sphingosine backbone instead of glycerol

2 types are sphingomyelin which has a phosphorglycholine head group and glycolic that have a carbohydrate head group

These are important for cell recognition and the nerve cell membrane (myelin sheath)

3 classes of lipids: Sterols (Cholesterol)

Smaller than the two others

Structure: Single polar hydroxyl (-OH) head, 4 carbon rings (steroid structure), short nonpolar hydrocarbon tail

Its function is it adds stability and fluidity to membranes, hydrophilic head interacts with phospholipid head, hydrophobic tail interacts with fatty acid tails in the bilayer

Components of the lipid bilayer

Phospholipids - basic building block

Cholesterol - maintains fluidity

Protein - all of cell membrane functions

Carbohydrates - binds to lipids and proteins, plays roles in signalling and communication

Lipid rafts

They are subdomains of the plasma membrane and contain a variety of proteins, especially those involved in cell signalling

They contain high contractions of cholesterol and glycosphingolipids

They are ordered and tightly packed then the surrounding bilayer, also float freely in the membrane bilayer

Micelles

They have a hydrophilic head that faces outwards and hydrophobic tail forming the core

Internal lipophilic zone makes the core ideal for hydrophobic drugs such as antibiotics, chemotherapy and anti migraine drugs

They help to improve drug solubility and makes efficient delivery

Liposomes

Aqueous core surrounded by a lipid bilayer which can be natural or synthetic

Biocompatible, biodegradable, non immunogenicity

Hydrophilic drugs go in the core, hydrophobic drugs go in the bilayer

Able to encapsulate a wide range of substances like antibiotics, hormone enzymes, vaccines, genetic material and other protiens

Liposomes vs Micelles

Liposomes: Structure - Bilayer of amphipathic molecules, Core - Hydrophilic, Surface - hydrophobic outer layer, Size - large and variable, Use- drug delivery system

Micelles: Structure - monolayer of amphipathic molecules, Core - Hydrophobic, Surface - hydrophilic outer layer, Size - Smaller, Use - drug delivery especially with hydrophobic drugs

Lysosomal therapies

2 therapies for lack of lysosome enzymes or component, both help to break down storage materials reducing cell damage

1. Therapies that reduce biosynthesis of the accumulating substrate - substrate reduction therapies - substrate precursors - substrate