Quick Facts• Primary purpose is to maintain the internal environment of cells by regulating what goes in and what comes out.• Average width: 0.01μm• Primary components:

• Phospholipid bilayer• Protein molecules• Glycoproteins and glycolipids • Cholestrol: steroid that stabilizes the membrane

Phospholipids

Carbohydrate groups and ProteinsCarbohydrate

groups on glycoproteins and

glycolipids• Form antigen (label identifying cell as “self”)

Proteins• Facillitate the movement of substrate across the membrane

7-9nm thick (nucleus & ER membranes = 5-7nm)

All biological membranes are the same : fluid-mosaic model§ phospholipid bilayer, proteins, carbohydrates and cholesterol

Membranes are fluid structures - individual lipid molecules & some proteins move about within the layers

Phospholipids§ Hydrophobic tails will face away from water to form a monolayer or micelle (if tails

are short)§ Therefore membrane is impermeable to water soluble (polar) molecules

Proteins carry out most other membrane functions,§ they are located throughout the membrane (hence the term mosaic)§ can cross both layers OR be confined to one§ Provide channels for water-soluble molecules & ions to pass

Cholesterol (between the phospholipid molecules)§ makes the membrane less fluid & more stable

Carbohydrates are usually on the outer surface & linked to protruding proteins

Membranes

How does it regulate molecular transport?

Passive Transport• Diffusion• Osmosis• Facilitated diffusion (channel & carrier mediated)

Active Transport• Primary (uses chemical energy)• Secondary (uses electrochemical gradient)

Passive transport: Diffusion•Relies on molecules being small enough to pass through the semi-permeable membrane …• or in the case of channel-mediated diffusion, can be through a protein channel•Movement of molecules governed by the concentration gradient (high to low)•Diffusion ceases when balance is achieved•Diffusion animation

Passive transport: Osmosis• Occurs when molecules of a substrate are too large to pass through the semi-permeable membrane• Substrate molecules do not move, instead water crosses the membrane in order to achieve balance (low to high)• Diffusion ceases when balance is achieved• Osmosis animation

Solute

Solvent(eg. Water)

Passive transport: Facilitated diffusion•Molecules of substrate are unable to permeate the membrane but are instead transported through specialised protein channels.•Proteins change shape to facilitate movement•Molecules are transported along the concentration gradient (high to low)•Diffusion ceases when balance is achieved•Facilitated diffusion animation

Facilitated diffusion

Primary active transport•Active transport involves molecules moving against the concentration gradient•Molecules are transported along protein channels, proteins change shape to facilitate movement•Requires the input of energy in the form of ATP (Adenosine triphosphate)•Allows cell to retain ideal intracellular environment even when concentration of required ions in extracellular environment is low.•Primary active transport animation

Secondary active transport•Same purpose as in primary active transport except …•ATP is not required to power the protein pump.•Instead, energy is gained by moving another substance in or out of the cell, but along the concentration gradient.•A bit like a wind-up toy, an input of energy will result in the output of energy,•Secondary active transport animation

Bulk transport•Substrate can be moved in bulk by packaging it in a vesicle that either merges with the plasma membrane or breaks off from it.•Substrate exits the cell via EXOCYTOSIS•Substrate enters the cell via ENDOCYTOSIS, of which there are 3 types:

• Phagocytosis (taking in solids)• Pinocytotsis (taking in liquids)• Receptor mediated endocytosis

•Bulk transport animation

Endocytosis

Exocytosis

• Isotonic: (iso - same) surrounding fluid and cells internal fluid are of equal concentration

• Hypotonic: (hypo - lower) surrounding solution has a lower concentration than the cells.Water will diffuse through the membrane into the cells

• Hypertonic: (hyper - higher) surrounding solution has a higher concentration than the cells

Mitochondrion

Golgi apparatus

Centriole

smooth ER

Lysosome

Cytoplasm/Cytosol

Plasma membrane Cell Wall

Ribosome

rough Endoplasmic Reticulum (ER)

Nucleus

nuclear pore

nucleolus

nuclear membrane

Eukaryote’s nuclear envelope is a double membrane

Prokaryotes lack a nuclear envelope DNA contains encoded instructions for every aspect of an organisms existence; structure, function and behaviour

DNA granular until mitosis, then DNA becomes organised into chromosomes

Nucleolus/nucleoli = aggregation of RNANuclear pores to allow movement between nucleus and cytoplasm

Control centreNucleus

Produces chemical energy in the form of adenosine triphosphate (ATP) through the process of cellular respiration

Outer & inner membraneThe inner membrane contains many folds to provide a larger surface area for energy production

ATP produced by reactions on inner membrane

Only in eukaryotes

Energy supplying organelleMitochondrion

Synthesize proteins through the addition of amino acids

Receive coded instructions via mRNAComposed of protein and rRNA (ribosomal RNA)

Free ribosomes in the cytosol make proteins for local use

Ribosomes connected to the ER make proteins for other parts of the cell or for export

Protein factoriesRibosomes

Ribosomal products

Cell Type Protein Function Kept / exported

RBC Haemoglobin Carry O2 Kept

Pancreas Insulin Control glucose levels

Exported

Muscle Actin / Myocin

Movement Kept

Stomach Pepsin Digestion Exported

Liver Catalaze Speed up reaction

Both

Network of intracellular membranesPrior to transport, packages substances in a transport vessicle

Production, processing, transport & storage of materials within a cell

Links with plasma membrane and other membranous organelles

Intracellular transportEndoplasmic Reticulum

Stack of flat membrane sacsCollects identical proteins and condenses them in to a single export unit

Packages protein bundles in to excretory vessicles

Concentration and packagingGolgi Apparatus

Organelles in action

Large membrane-bound vessicles containing digestive enzymes

Used for breaking down unwanted structures or substances within the cell

Malfunction results in build up of toxic substances within the cell

Animation

Controlled destructionLysosome

Peroxisomes § Prevent the dangerous build-up of hydrogen peroxide (a

byproduct of some cellular processes)

Endosomes § pass newly ingested material to lysosomes for digestion

Cilia & Flagella§ used for movement in many prokaryotic cells & some

eukaryotes§ covered by an extension of the cell membrane§ made up of 9 doublet microtubules & 2 single, central

microtubules

Other organelles

Cytoplasm

A ribosome on the ER assembles around the mRNA, every 3 nucleotides codes a particular amino acid

The protein is packaged in a transport vessicle and transported through the cell along the ER

How it all comes togetherProtein production to excretion

An mRNA copy of a gene on the DNA is made. This copy then travels out in to the cytosol

Proteins are concentrated and then packaged in to a secretory vessicle.

Vessicle floats through the cytosol before merging with the plasma membrane

Nucleus

Ribosome

ER

Golgi Body

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SummaryOf structures and functions

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Membrane bound (called a tonoplast in plants), liquid filled spaces

food vacuoles (intracellular digestion)contractile vacuoles (water balance)plant cells typically have large ones filled with sap (turgidity & storage)

Present in plants, fungi, some protists, bacteria & animalsVacuole

Double membrane, inner membrane contains many inner folds

Contains DNA, free ribosomes, starch grains and lipid droplets

Folded inner membrane forms thylakoids, stacks of these are called grana

The light-dependent reaction occurs in the chlorophyl containing grana

The light-independent reaction occurs in the fluid around the grana called the stroma

Only plants cells contain chloroplasts. Photosynthetic bacteria contain chlorophyll, but it is free-floating within the cell.

Sunlight trappersChloroplasts

Only in plant, fungi & bacterial cellsPrimary cell wall made of non-living cellulose (chitin in fungi and bacteria)

Plants have secondary cell walls made of ligninThe walls of two cells are connected by a sticky pectin layer

Provides support, strength & prevents expansion

Freely allows water & dissolved substances through

Rigidity and supportCell Wall

The cell skeletonMaintain the shape of the cellProvide a support structure for the

components of the cellMovement of materials within cellMovement of the cell itself - if required

Maintain the shape of the cellProvide a support structure for the

components of the cellMovement of materials within cellMovement of the cell itself - if required

Microtubules

• Hollow• Composed of tubulin

Microfilaments

• Solid• Thinner• More flexible

Intermediate filaments

• Very tough• Composed of proteins

Occluding (tight) junctionsCell membranes “come

together”Function:

• hold cell together• help to maintain polarity

of cell• prevent passage of

molecules

NO movement of material between cells

Communicating (gap) junctionsAligned protein channels in the membranes of adjoining cells

Permit the passage of: amino acids, sugars, salt ions, and other small molecules

Anchoring junctions (Desmosomes)

Dense plaques of protein anchoring intermediate filaments that protrude in to the cytosol of neighbouring cells

Serve as a bridge connecting the actin cytoskeleton of neighbouring cells

Connections between plant cells: plasmodesmata

Signal to apoptose may come from inside or outside the cell

Cell death via apoptosis is a normal part of the cell cycle

Failure to apoptose will result in uncontrolled growth and reproduction.

Invasion in to healthy cells represents a malignant tumour

Cancer is the second highest cause of death in humans after heart disease

Animation of difference between apoptosis and necrosis

Programmed cell deathApoptosis

Apoptosis The sequence of events