Cell Biology Overview

Cell Theory

• Cells are the basic unit of life
• All living things are made up of cells
• All cells come from other cells

Cell Growth

• Single-celled organisms grow as the cell grows
• Multicellular organisms grow by adding cells through cell division

Types of Cells

• There are many different types of cells
• Cells can be very different from one another, even within the same organism
• Cells specialize to carry out different functions

Nerve Cells

• Nerve cells are long and thin, like wires
• They carry nerve impulses throughout the body

Muscle Cells

• Muscle cells can contract to provide movement

Skin Cells

• Skin cells are flat and strong to protect the body

Bone Marrow Cells

• Bone marrow manufactures blood cells
• Blood cells carry oxygen through the blood

Differentiation

• The process of a young cell maturing to specialize and become a particular type of cell is known as differentiation

Cell Structure

• All cells are surrounded by a lipid bilayer membrane
• The membrane encloses and contains the contents of the cell
• Many lipids are amphipathic, having both hydrophobic and hydrophilic parts on the same molecule

Lipid Bilayer

• In an aqueous or polar environment, amphipathic molecules arrange themselves in complexes (aggregates of molecules)
• The hydrophobic parts of the molecules face inward, away from the water
• The hydrophilic parts of the molecules face outward, towards the water

Cell Membrane

• The lipid bilayer forms a membrane around the cell
• The hydrophilic portions of lipid molecules face the aqueous environments on both the inside and outside of the cell
• The hydrophobic parts lie in the center of the bilayer and form a barrier that blocks many molecules from crossing the membrane

Selectively Permeable Membrane

• The cell membrane is selectively permeable
• Certain types of molecules can pass through the membrane, while others cannot

Eukaryotic and Prokaryotic Cells

• There are two major categories of cells: eukaryotic and prokaryotic
• All organisms are made up entirely of either eukaryotic or prokaryotic cells

Eukaryotes

• Eukaryotes have a nucleus and other membrane-bound, internal structures called organelles
• Organelles compartmentalize some of the functions of the cell

Prokaryotes

• Prokaryotes do not have a nucleus
• Their genetic material is all together in the cytoplasm
• Prokaryotes are mostly unicellular, with some having colonial or multicellular stages of life
• Prokaryotes have faster division rates
• Prokaryotes can adapt quickly to drastic changes in the environment

Differences Between Eukaryotes and Prokaryotes

• Eukaryotes can carry out more complex and efficient biochemical reactions because reactions can be isolated in membrane-bound compartments
• Prokaryotic biochemical reactions are simpler and must all occur in the cytoplasm, where more complex reactions might interfere with each other

Nucleus

• The nucleus contains the cell's genetic material (DNA)

Organelles

• Organelles are membrane-bound structures within the cytoplasm of eukaryotic cells
• They perform specific functions in the cell

Cytoplasm

• The cytoplasm is the gel-like substance that fills the cell
• It contains the organelles and other cellular components

Ribosomes

• Ribosomes are responsible for protein synthesis
• They are found in both eukaryotic and prokaryotic cells

Endoplasmic Reticulum (ER)

• The ER is a network of membranes that extends throughout the cytoplasm
• It is involved in protein synthesis, folding, and transport
• There are two types of ER: rough ER and smooth ER

Rough ER

• Rough ER has ribosomes attached to its surface
• It is involved in protein synthesis and folding

Smooth ER

• Smooth ER does not have ribosomes attached to its surface
• It is involved in lipid synthesis, detoxification, and calcium storage

Golgi Apparatus

• The Golgi apparatus is a stack of flattened sacs that modify, sort, and package proteins and lipids
• It is involved in the secretion of these substances

Mitochondria

• Mitochondria are the powerhouses of the cell
• They are responsible for cellular respiration, which produces ATP (adenosine triphosphate), the cell's energy currency

Lysosomes

• Lysosomes are membrane-bound sacs that contain digestive enzymes
• They break down waste materials, cellular debris, and invading pathogens

Vesicles

• Vesicles are small membrane-bound sacs that transport materials within the cell

Centrioles

• Centrioles are involved in cell division
• They help to organize the microtubules that form the spindle fibers

Microtubules

• Microtubules are hollow cylinders that provide structural support, aid in cell movement, and transport materials

Flagella

• Flagella are long, whip-like structures that help cells to move
• They are found in some prokaryotic and eukaryotic cells

Cilia

• Cilia are short, hair-like structures that help cells to move or to move fluids past the cell
• They are found in some eukaryotic cells

Cell Wall

• The cell wall is a rigid structure that surrounds plant, bacterial, and fungal cells
• It provides structural support and protection

Capsule

• Some bacteria have a capsule that surrounds their cell wall
• The capsule helps to protect bacteria from the immune system and from dehydration

Plasma Membrane

• The plasma membrane is the outer membrane of the cell
• It controls the movement of substances into and out of the cell

Cytosol

• The cytosol is the fluid component of the cytoplasm
• It is mostly water and contains dissolved substances, such as proteins, ions, and sugars

Chromatin

• Chromatin is the material that makes up chromosomes
• It is composed of DNA and proteins