The Cell: Basic Unit of Life

Discovery of Cells• Discovered in 1665 by Robert Hooke,

English scientist and inventor of the light microscope

Cell Theory• Cells are the building blocks of living

organisms and the basic unit of life• All cells come from other cells• Cells contain hereditary information which

control all cell function• All metabolism (the chemical reactions of

life) occurs within the cell

Biological size and cell diversity

• Some cellular processes depend on the surface area for efficiency. Ex: Diffusion depends on surface area. The greater the surface area, the greater the rate of diffusion.

• Other cellular processes depend on volume. Ex: the making of large proteins requires greater volume in the cell

• Therefore the Surface Area to Volume Relationship is important in living organisms

Cell Size

Cell Surface Area-to-Volume Ratio• For a 1 cell organism such as a bacterium,

getting its oxygen would be through simple diffusion. However, simple diffusion cannot satisfy the requirements for larger organisms—it would take several years!!!

• The plasma membrane of cells must be large enough relative to cell volume to regulate passage of materials

• Cell size and shape are related to its function!!!

Cell Surface Area-to-Volume Ratio

1. Light Microscope: referred to as compound microscope, used by most students

• Two features determine how clearly an object is viewed

1. Magnification2. Resolution

• Light microscope has 500 times more resolution than human eye

Technologies Used To Study Cells

2. Electron Microscope• Developed in the 1950s• Allows study of the ultrastructure of cells• 10,000 times more resolution than human eye• Types of Electron Microscopes:

1. Transmission Electron Microscope (TEM)• Used to see the internal structure (ultra structure) of cells

2. Scanning Electron Microscope (SEM)• Used to produce 3D images of surfaces

Technologies Used To Study Cells

Comparing Light & Electron Microscopy

TEM: Tongue With Taste Bud

SEM: Human Embryo at Day 3

SEM: Human Embryonic Stem Cells

SEM: Tooth Plaque

SEM: Cluster of Breast Cancer Cells

SEM: Osteoporosis Bone

SEM: Red Blood Cells

SEM: Nerve Cells

SEM: Blood Clot

SEM: Lung Cancer Cells

SEM: Isabela Implanting onto the wall of the uterus

SEM: Split Human Hair

3. Freeze-Fracturing• Living material is plunged into liquid nitrogen

(-196 ºC) and pushed against a blade in a precise way

• Frozen tissue splits along lines of weakness, often in the middle of a membrane

• The fractured surfaces are “etched” with a heavy metal so that they can be seen using TEM

• Used to determine function of organelles

Technologies Used To Study Cells

Freeze Fractioning

Freeze Fractioning: Blood Vessel in a Melanoma

Prokaryotic Cells• DNA is not enclosed by a nucleus• Bacteria

Eukaryotic Cells• DNA is enclosed by a nucleus• Highly organized membrane-enclosed

organelles• Animal, plant, fungi & protists

Types of Cells

Functions of cell membranes:• Divide the cell into structures that carryout specialized

activities, Organelles:Mitochondion Endoplasmic reticulumRibosomes VacuolesGolgi Complex ChloroplastsNucleus Nucleolus

• Interacting membranes form endomembrane system• Vesicles transport materials between compartments

Intro To Cell Membranes

Diagram ofa plant cell

Diagram ofan animal cell

Nucleus• Contains the cell’s DNA• Bounded by

– Nuclear envelope– Double membrane perforated with nuclear pores

• DNA forms chromatin, which is organized into chromosomes

Nucleolus• Located inside the nucleus• Its purpose is to make ribosomes

Cell Organelles

The cellnucleus

Cell Organelles

Plasma Membrane• Physically separate cell interior from

extracellular environment• Regulates passage of materials• Participates in biochemical reactions• Receives information about environment• Communicates with other cells

The Fluid Mosaic Model of the Plasma Membrane

• It consist of a fluid Phospholipid Bilayer with a “mosaic” pattern of numerous proteins such as structural proteins and transport proteins

• The Phospholipid Bilayer is Amphipathic because it contains both:

• Hydrophobic regions• Hydrophilic regions

Phospholipid Bilayer

Fluid Mosaic Model of the Plasma Membrane

Endoplasmic Reticulum (ER)• Network of folded internal membranes in the

cytoplasm

• Two Types of ER:1. Smooth ER

• Site of lipid synthesis• Site of detoxifying enzymes• Does not have Ribosomes attached to its surface

2. Rough ER• Has Ribosomes attached to its surface• Ribosomes manufacture proteins• Proteins may be moved into the ER lumen

Cell Organelles

EndoplasmicReticulum (ER)

Cell OrganellesGolgi Complex• Membrane complex that processes, sorts, and

modify proteins

• In animal cells, Golgi complex also manufactures lysosomes (sacs which contain enzymes that breakdown materials)

• Golgi Complex modifies carbohydrates and lipids and packages into vesicles, which are then transported out of the cell.

Golgi Complex

Cell Organelles

Lysosomes • break down worn-out cell structures,

bacteria, and other substances Peroxisomes• Involved in lipid metabolism and

detoxification• Contain enzymes that produce and

degrade hydrogen peroxide

Lysosomes

Cell Organelles

Mitochondria “The Powerhouse of the Cell”

• Responsible for the brake down of nutrients and the transfer of energy from the nutrients to ATP through a process called Cellular Respiration.

• As a by-product of Cellular Respiration, Carbon Dioxide & Water are produced

• Most metabolic reactions within the cell take place in the Mitochondia

Mitochondria

Cell OrganellesChloroplasts • Place where Photosynthesis occurs• During Photosynthesis, Chlorophyll traps

light energy• Light energy is converted to chemical

energy (ATP) to make Glucose• As a by product of Photosynthesis,

Oxygen is produced

Chloroplast

Cellular Respiration and Photosynthesis

Cell OrganellesCytoskeleton • Internal framework of fibers made of:

– Microtubules– Intermediate filaments– Microfilaments

• Provides structural support for the cell• Involved with transport of materials in the

cell

TheCytoskeleton

Cell Organelles

Cilia– Thin, movable structures that project

from cell surface– Function in movement

Flagella– Tail-like projections– Function in movement

Cilia

Flagella