CELL STRUCTURE AND FUNCTION OF ORGANELLES

IN THIS TOPIC

Structure and functions : Cell wall Cell membrane Organelles

Movement of molecules/substances in and out of the cell

CELL WALL

Outside the cell membrane

In plant cell, prokaryotes, some protista and fungi only.

Components : middle lamella primary wall secondary wall Plasmodesmata

Land plants : Cellulose Lignin Suberin

Waxy Waterproof (some tissue)

Functions : Cell shape Support and mechanical strength Prevent haemolysis ‘skin’ Carbohydrate store

CELL MEMBRANE

Both in animal and plant cell

Selective permeable

Composed of : Proteins Glycoprotein Glycolipids Phospholipid Cholesterol and lipoprotein (a few)

Fluid mosaic model

Lipid bilayer Phospholipid Hydrophilic head (polar) Hydrophobic tail (non-polar)

Embedded protein Embedded between layer Integral protein Peripheral protein (not embedded) Free movement within layer As carrier and channel protein

Cholesterol Make phospholipid stay in position

‘Fluid’ protein and lipid molecules able to shift and move laterally

‘Mosaic’ the protein molecules form mosaic-like patterns when viewed

from the top.

Functions of cell membrane

Barrier Maintain internal environment of

cell Communication between cell Markers to foreign materials Transportation

(Text book page 29)

ORGANELLES

1. Nucleus2. Endoplasmic reticulum3. Golgi apparatus4. Mitochondria5. Lysosomes6. Ribosomes7. Chloroplasts8. Centrioles9. Vesicles

Nucleus

Nucleus

‘The Control Centre’

Available in all eukaryotes excepts ; Sieve tube of phloem R_ _ _ _ oo _ _ _ l l

Components of nucleus

nuclear envelope

nucleoplasm

nucleolus

chromatin

Nuclear envelope

Two outer membranes (lipid bilayers) Innermost surface has DNA attachment

sites

Nuclear porebilayer facing cytoplasm Nuclear envelope

bilayer facing

nucleoplasm

Nucleolus dark spot in the middle of the nucleus produce ribosomes

Functions : Store genetics material and information

Site of cell division Produce RNA & DNA

Endoplasmic reticulum

In animal cells, continuous with

nuclear membrane

Extends throughout cytoplasm

Two regions - rough and smoothRough ER Smooth ER

Functions

ROUGH ER SMOOTH ER

Prominent in cells that manufacture protein for export ; digestive enzymes, hormones, structural protein or antibodies

Necessary for steroid synthesis, metabolism and detoxification of substances in liver, phospholipid synthesis and excitation-contraction coupling in skeletal muscle

With ribosome Without ribosome

Golgi body

Puts finishing touches on proteins and lipids that arrive from ER

Packages finished material for shipment to final destinations

Material arrives and leaves in vesicles

Mitochondria

ATP-producing powerhouses

(aerobic respiration)

Membranes form two distinct

compartments

ATP-making machinery

embedded in inner

mitochondrial membrane

outercompartment

innercompartment

outer membrane inner membrane

repeated foldings of inner membrane (cristae)

Lysosomes

a vesicle with enzymes digest biological macromolecules ER to Golgi body Autophagy Autolysis

Ribosomes

Function as the site of mRNA translation during protein synthesis

Free-wheeling in cytoplasm / attached to ER

TWO subunits ; small and large

Chloroplasts

Site of photosynthesis

Centrioles

Type of cytoskeleton (network of fiber) In mitosis; source of mitotic spindle Functions ;

Organise the formation of spindle fiber Organise the formation of cilia and flagella

(9+2 / 9+3)

vesicles

a sac In cytoplasm Types ;

Lysosome Peroxisome Shuttle vesicles Secretory vesicles Endocytosis vesicles Storage vesicles

♫ ♪ Take 5 ♫ ♪

MOVEMENT OF MOLECULES/SUBSTANCES IN AND OUT OF THE CELL

The movement of molecules are based on concentration gradient

Concentration gradient ; Means the number of molecules or ions in one

region is different than the number in another region

In the absence of other forces, a substance moves from a region where it is more concentrated to one where it’s less concentrated - “down” gradient

Passive transport

Active transport

Endocytosis

Exocytosis

PASSIVE TRANSPORT

Does not require ATP High to low of concentration gradient

Types ; Diffusion Osmosis Facilitated diffusion

Diffusion

movement of molecules or ions down a concentration gradient

the molecules move using a natural kinetic energy

what determines the rate of diffusion?

Steepness of concentration gradient◦ Steeper gradient, faster diffusion

Molecular size◦ Smaller molecules, faster diffusion

Temperature◦ Higher temperature, faster diffusion

Surface area◦ Higher surface area, faster diffusion

Molecules that diffuse through cell membranes

Oxygen – Non-polar so diffuses very quickly.

Carbon dioxide – Polar but very small so diffuses quickly.

Water – Polar but also very small so diffuses quickly.

Simple Diffusion

small, nonpolar molecules

(ex. O2, CO2)

Polar molecules(ex. Glucose, water)

ions(ex. H+, Na+, K+)

LIPID-SOLUBLE WATER-SOLUBLE

LIPID-SOLUBLE

Facilitated diffusion

movement of molecules or ions down a concentration gradient with the help of transport protein

Types of transport protein ; Carrier protein Channel protein

glucose transporter

solute (glucose)

low

[ conc’n] of glucose outside cell > inside

Glucose binds

Protein change shapeGlucose is exposed to fluid on the

other side of the membrane, detaches, leaves channel

Osmosis

Water movement across a partially permeable

membrane from an area of high

water potential (low solute concentration) to an area of low water potential (high solute concentration)

HypotonicSolution

membrane permeable towater but not to solutes

HypertonicSolution

Tonicity 2% sucrosesolution

distilled water

10%sucrose solution

2%sucrose solution

Hypotonic Conditions

Hypertonic Conditions

Isotonic Conditions

Isotonic solution Hypotonic solution Hypertonic solution

H2O H2O

(1) Normal (2) Lysed

H2O

H2O H2O H2O

Animalcell

Plantcell

(4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed)

(3) Shriveled

Plasmamembrane

H2O

H2O

ACTIVE TRANSPORT

Transport of molecule

Low to high of concentration gradient

require ATP

Involves carrier protein

ATP

ADP

Pi

higher calcium concentration

lower calcium concentration

Calcium enter tunnel

Calcium pump

ATP transfer a phosphate group

Shape change –Ca release

Shape returns o its resting position

ENDOCYTOSIS

Transport of macromolecules

Involves formation of vesicle

Into the cell

Two types; Phagocytosis Pinocytosis

phagocyticvesicle

ediblebacterium

amoeba

Phagocytosis

Phagocytosis; “cellular eating”.

In phagocytosis, the cell engulfs a particle by extending pseudopodia around it and packaging it in a large vacuole.

The contents of the vacuole are digested when the vacuole fuses with a lysosome.

In pinocytosis; “cellular drinking”

a cell creates a vesicle around a droplet of extracellular fluid.

EXOCYTOSIS

Transport of molecules Out of a cell Enclosed in vesicle Move to cell surface membrane Fuse release

Both diffusion and facilitated diffusion are forms of passive transport of molecules down their concentration gradient, while active transport requires an investment of energy to move molecules against their concentration gradient.

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