Cells

Chapter 7

The size range of cells

Why are cells so small?

Small cells have a high surface area to volume ratio which allows more stuff to move in and out of the cell

CELL THEORY

• Living organisms are composed of one or more cells

• Cells are the smallest unit of life• Cells come from other cells

ALL CELLS HAVE

• Plasma membrane – Outer layer

• Cytoplasm – Watery stuff inside

• DNA– Genetic material

TWO BASIC CELL TYPES

Prokaryotic Cells

• DNA in nucleoid region

• No membrane-bound organelles

• No nucleus• Small• Bacteria

Plasma Membraneaka: The Gate-keeper

Overview of an Animal Cell

Overview of a Plant Cell

Nucleus & Nuclear Envelope

Ribosomes

Endoplasmic Reticulum (ER)

Golgi Apparatus

LysosomesSac of hydrolytic enzymes

Digests macromoleculesBreaks down dead organelles

pH ~ 5

Formation & Function of Lysosomes

The Endomembrane System

MitochondriaSite of Cellular Respiration, Makes ATP

ChloroplastSite of Photosynthesis

Converts energy from sunlight to chemical energy stored in sugar

Central Vacuole: Plant Cells

StoresWaterWasteNutrients

Makes plant cell turgid

PeroxisomesProduce and break down H2O2

Do not bud from the Endomembrane System

Cytoskeleton

• Network of fibers throughout cytoplasm

• Gives cell shape

• Holds organelles in place

• Involved in movement & changing shape

Motor Molecules & Cytoskeleton

Changing shapeCilia movementFlagella movement

Organelles move along microtubule or microfilamentEx: Vesicle transport

Centrosomes & Centrioles• Pair of centrioles w/in centrosome

– Centriole: 9x3 ring of microtubules

• Microtubules grow out of centrosome

• Most plant cells lack centrioles

Structure of Eukaryotic Cilia/ Flagella9x2 + 2 ring of microtubulesCovered in plasma membrane

Basal BodyAnchors cilia/ flagella to cell9x3 ring of microtubules

Wave

Back and forth

Dynein “walking” moves Cilia and Flagella

•Powered by ATP•Dynein arms grip adjacent microtubule•Grip, pull, release – repeat•Results in bending of microtubules

Microfilaments (actin filaments)• Pulling force

– Muscle contraction– Cytoplasmic streaming– Pseudopodia

• Part of Extracellular Matrix– Support cell membrane– Inside of cell membrane

Extracellular Matrix

Plant Cell Walls• Protects cell• Gives cell shape• Prevents excessive uptake of

H20• Primary, secondary walls

• Plasmodesmata– Cell to cell communication

– Cytoplasm continuous from one cell to other

• Middle lamella cements cells together

Cell Junctions in Animal Cells

Fuses membranesStrong sheets

Pass ions and small molecules