The Cell

Chapter 4

Cells

Marks the boundary between the “living and the dead”

Structural and functional unit of an organism

Smallest structure capable of performing all of the functions necessary for life

What is a cell?

Why do we care? We have TRILLIONS of them!! (@65) Every organism is composed of

one or more cells Basic unit of structure and function in organisms All come from pre-existing cells

Cell Theory

Why are Cells so Small????

Large cells have far less surface for each unit of volume than do small cells

All cells…….

Have an outer plasma membrane Contain DNA

Enclosed within the cell somewhere Contain cytoplasm

Plasma Membrane

All cells surrounded by a plasma membrane Phospholipid bilayer forms spontaneously

whenever a collection of phospholipids is placed in water

Cytoplasm material inside a cell

is the cytoplasm Everything between

the plasma membrane and the region of DNA

Gives cells their shape

Assist in movement of cell and organelles

Microscopes

Compound light microscope Multiple lenses

increase magnifying power

Two basic kinds of cells Prokaryotic

Nothing separates the DNA from internal cell parts

Eukaryotic Contain organelle sacs Nucleus – contains the

DNA

Eukaryotic Cells

Examples of Eukaryotic Cells: Animal Plant Fungi Protozoa

Organelles Organelles act as their own separate

“organs” They physically isolate chemical reactions

inside cells Animals and plants will differ in their organelles

Nucleus Encloses the DNA of a

eukaryotic cell Contains chromosomes Functions:

Prevents DNA from getting entangled with structures in the cytoplasm

Outer membranes act as a boundary

Components of the nucleus Nuclear pores Nuclear envelope Nucleolus Nucleoplasm DNA

Chromosomes Chromatin

Nuclear envelope Double-membrane

system composed of lipid bilayer (with pores)

Bilayers surround the fluid part of nucleus (nucleoplasm)

Continuous with the endoplasmic reticulum

Nucleolus

Dense mass located within the nucleus

Produces ribosomes

Ribosomes Site of protein

synthesis Occurs in the cytoplasm

Attached to the endoplasmic reticulum

Differ between prokaryotes and eukaryotes Why is this important

from a health aspect?

Endomembrane System Helps modify proteins into final form

Lipids are assembled Compartmentalizes the cell Main components:

1. Nuclear envelope 2. Endoplasmic reticulum (ER) 3. Golgi body 4. Various vesicles (transport)

1. Nuclear envelope Merges with the

membrane of the ER Consists of

membranous channels and saccules

2. Endoplasmic Reticulum Channel that snakes

through the cytoplasm Lipids assembled and

polypeptide chains modified into final proteins

Can be rough or smooth Dependant on the

attachments of ribosomes Rough ER

Processing and modification of proteins

Smooth ER Synthesizes phospholipids

3. Golgi Body (Apparatus) Series of flattened

sacs Collects, sorts,

packages, and distributes materials such as proteins and lipids

Contain enzymes that put the finishing touches on proteins and lipids

4. Vesicles Enzymes from golgi apparatus sort and

package the molecules into vesicles Tiny sac that moves through cytoplasm Function in transport, storage, or digestion of

substances Two main types:

Lysosomes Peroxisomes

Lysosome A lysosome is a

membrane-enclosed sac contains digestive

enzymes to break down: Macromolecules damaged organelles

Put it all together……

Organelles That Contain DNA Eukaryotic cells contain cell-like organelles

that, besides the nucleus, also contain DNA these organelles appear to have been derived

from ancient bacteria that were then assimilated by the eukaryotic cell

they include the following organelles: Mitochondria Chloroplasts

Energy-Related Organelles organelles specialize in

converting energy to a form that can be used by the cell Requires solar energy Dissipates as heat

Chloroplasts Use solar energy to

synthesize carbohydrates Carbohydrates then

broken down in the….. Mitochondria

Produce ATP molecules

Energy-Related Organelles

Photosynthesis Cellular Respiration The chemical energy of

carbohydrates is converted at ATP

DNA in mitochondria?? mtDNA

Inherited solely from mother

First set of DNA to be sequenced

Endosymbiotic theory Helps in evolutionary

inheritance

Organelles That Contain DNA

The theory of “endosymbiosis” states that some

organelles evolved from a symbiosis

one cell of a prokaryotic species was engulfed by and lived inside of a cell of another species of prokaryote

Organelles That Contain DNA Other evidence supporting endosymbiotic theory:

Mitochondria are about the same size as modern bacteria

The cristae in mitochondria resemble folded membranes in modern bacteria

Mitochondrial ribosomes are similar to modern, bacterial ribosomes in size and structure

Mitochondria divide by fission, just like modern bacteria

Cytoskeleton – Cytoplasm System of

interconnected fibers, threads, and lattices in the cytosol

Extend from nucleus to the plasma membrane

Gives cells their shape

Assists in movement of cell and organelles

Assemble and disassemble as needed

The three protein fibers of the cytoskeleton

The Cytoskeleton: Interior Framework of the Cell Centrioles

complex structures that assemble microtubules in animal cells and the cells of most protists

anchor locomotory structures

such as flagella or cilia

The Cytoskeleton: Interior Framework of the Cell vacuoles

membrane-bound storage centers

central vacuole filled with water and

dissolved substances

Outside the Plasma Membrane Cell walls

found in plants, fungi, and many protists

comprised of different components than prokaryotic cell walls

function in providing protection, maintaining cell shape, and preventing excessive water loss/uptake

Outside the Plasma Membrane

Extracellular matrix (ECM) takes the place of the cell wall

in animal cells and is comprised by a mixture of proteins secreted by the cell

collagen and elastin proteins

Form a protective layer over the cell surface

fibronectin protein Connects the ECM to the

plasma membrane integrins

Connected to fibronectin Proteins that extend into the

cytoplasm of the cell

Plant Cells

Cell wall Central vacuole Chloroplasts

Fungal Cells Mold or yeast Spores Cell wall Unicellular or

multicellular

Protozoa Cells

No cell wall Unicellular Motility

Prokaryotes

ArchaeBacteria

“Micro”organisms

Characteristics of Cells

Prokaryotic cells ~1.0 µm in diameter All are microorganisms Unicellular Bacteria and Archaea no nucleus no membrane-bound

organelles

Prokaryotes – General cell structure Nucleoid Pili Fimbriae Flagella Cell wall Glycocalyx Ribosomes