Eukaryotes and Prokaryotes

Structure of the plasma membrane

Bilayer, mostly phospholipids

Boundary of the cell

Function of plasma membrane

Allow communication with the external environment

Selectively permeable

What is the fluid mosaic model?

Proteins embedded in the bilayer can move sideways within the layer, giving it mobility

What do receptor proteins in the plasma membrane allow?

The cell to receive signals from the environment and pass them on to the inside of the cell

What do transport proteins in the plasma membrane allow?

Small molecules, such as ions, to enter and exit the cell

The flexibility of the plasma membrane allows

Cell growth and cell movement

Structure of phospholipids

Glycerol

Phosphate

Two fatty acid chains

Hydrophobic head or tail?

Tail

Hydrophilic heads or tails?

Head

Amphipathic

Molecules that have both hydrophobic and hydrophilic properties

Is the lipid layer 2D or 3D?

2D

What are liposomes?

Closed spherical vesicles formed when phospholipids are added to pure water.

This is due to the amphipathic nature of phospholipids. The hydrophobic tails are not exposed to water and the hydrophilic heads are.

What are the hydrophilic heads exposed to?

Water on the outside of the membrane

Name four roles of membrane proteins

• Transporters

• Anchors

• Receptors

• Enzymes

Describe transporter proteins.

Transport tridents, metabolites and ions across the bilayer

Describe anchor proteins

Anchor the membrane to macromolecules

Describe receptor proteins

Detect chemical signals in the environment and transmit them to the interior of the cell

Describe enzymes.

Catalyses specific reactions

What are the two types of membrane proteins?

Integral

Peripheral

Name three integral membrane proteins.

• Transmembrane proteins

• Monolayer-associated proteins

• Lipid-linked proteins

Transmembrane proteins

Stretch across the lipid bilayer as a single a-helix, as multiple a-helices or as a b-barrel.

Monolayer-associated proteins

Anchored to the cytosolic surface (the side of the membrane that faces the inside of the cell) via an amphipathic a-helix.

Lipid-linked protein

Attached to either side of the bilayer via a covalent attachment to a lipid molecule

Name a peripheral membrane protein

Protein-attached protein

Protein-attached protein

Attached to membrane by relatively weak non-covalent interactions with other membrane proteins

Organelles within prokaryotes

• Flagellum

• Plasma membrane

• Cell wall

• Capsule

• Cytosol

• Ribsomes

• DNA

+ Cilia on the outside

Features of the nucleus (4)

• Contains DNA

• Surrounded by double-membrane nuclear envelope, with nuclear pores which are gateways for molecules to move in and out, enabling communication

• Storehouse for genetic information

• Contains nucleolus and DNA associated with proteins that are packed together

Brief overview on gene expression

1. DNA synthesis (replication)

2. RNA synthesis (transcription)

3. Protein synthesis (translation)

Endoplasmic reticulum

• Made up of interconnected tubes and flattened sacs

• Rough ER and Smooth ER

• Location where the majority of cell membrane components and materials for export are made

• Continuous with the membrane of the nuclear envelope

RER

Rough ER

• Contains ribosomes

• Makes membrane and secreted proteins

• Manufactures lipids and proteins (by ribosomes bound to the rough ER surface)

SER

Smooth ER

• Makes membrane vesicles

What is the cytosol?

The fluid inside cells, where majority of the organelle’s proteins are manufactured

Differs from the cytoplasm as the cytosol is the fluid part and the cytoplasm is there cytosol and everything suspended within it such as organelles

Do cytosolic proteins have sorting signals?

No, they remain at their site of manufacture.

Protein signal sequence

• Majority of organelle proteins are manufactured in the cytosol (on ribosomes)

• Sorting signals within the amino acid sequence direct proteins to their requisite organelle

  • If a protein has a signal for the nucleus it gets sent there

• If there is no signal, it stays in the cytosol (some proteins function in the cytosol)

Protein signal sequence- ER pathway

• If the protein has an ER signal sequence, an SRP (signal recognition particle) binds to it

• The ribosome and growing protein get directed to the rough ER membrane

• Within the ER, proteins fold up, assemble with other proteins, form disulphide bonds and are enhanced with oligosaccharide chains

What are vesicles?

Membrane-enclosed sacs

What is the function of transport vesicles?

Move substances from one location to another

How do transport vesicles work?

• Vesicles bud off “pinches off” from the ER

• They capture free molecules in the lumen and molecules embedded in the membrane

• The vesicle fuses with the membrane of another membrane-enclosed compartment, transferring the captured molecules to that organelle

What is the Golgi Apparatus?

Stacked, flattened membrane sacs

What is the function of the golgi apparatus?

To process and modify new proteins and lipids

• Add specific chemical groups

• Target them to their destinations