Chapter 4: The Cell

The working unit of life

Cells

n All living things are made of cells n  Cells first appeared 3.5 billion years ago, and all cells have

descended from them n  Viruses are not cells but require other cells to function

n  Organisms can be: n  Unicellular: consisting of only one cell n  Multicellular: many cells working together

n  Cells are small

Cell sizes vary, but 10 µm (microns) is an average. (1/1000 of a centimeter)

Cells are individually specialized

n Neurons, myocytes, macrophages, epithelia, osteocytes…

2 major kinds of cells

n  Prokaryotes n  Bacteria and archaea (single-celled organisms) n  No nucleus

n  Eukaryotes n  Plants, animals, fungi

n  Unicellular or multicellular n  DNA is contained in a nucleus

Eukaryotic Cells

•  DNA is contained within nucleus •  Almost always require oxygen to survive •  Larger than prokaryotic cells •  Usually part of multicellular organisms

•  Many compartments within cell – Organelles: highly organized, specialized

structures within a cell

What’s in a cell?

•  Cell membrane: outer lining •  Sometimes called the plasma membrane

•  Nucleus

•  Cytoplasm: – Other organelles – Cytosol: jelly-like fluid – Cytoskeleton: internal scaffolding

Animal Cells: Protein Production pathway

Animal Cells: Protein Production pathway

Nucleus •  DNA is confined within the nucleus •  This organelle has a nuclear membrane

•  The “blueprints” (genes/DNA) stay in nucleus; information must be copied & transported out to the “factory” (cytoplasm)

Protein Production: From nucleus to the factory

•  The copy: Messenger RNA (mRNA) •  Other types of RNA exist

Protein Production: The Factory

•  Ribosomes – Read the mRNA and translate the information – Build a protein (polypeptide chain of amino

acids)

Protein Production: Decision Time

•  Where should the ribosome carry the mRNA & make protein?

Rough Endoplasmic Reticulum (RER)

or remain

“Free” Ribosomes

RER: secreted and membrane-bound proteins Free ribosomes: cytoplasmic & nuclear proteins

Rough Endoplasmic Reticulum

“Rough” because covered with bumpy-looking ribosomes The ribosomes are making proteins from the

information in mRNA Endoplasmic reticulum helps to fold and put the finishing touches are newly made proteins From the ER, proteins are transported to other places inside or outside the cell

Protein transport: The assembly line

•  Proteins made in the RER do not stay there

•  Transport Vesicles – Bits of the RER membrane “bud” off, taking a

small amount of the cisternal contents with it – The membrane surrounding these “buds” can

fuse with other membranes

Golgi Complex: Distribution center of the cell

•  Like the RER, a connected network of membranous sacs with internal spaces

•  Receives the contents of transport

vesicles from the RER that fuse to it

•  Processing, sorting, and shipping

Protein production

•  Ribosomes assemble amino acids into proteins

•  Parts of ribosomes are made in the nucleolus, a dark-colored part of the nucleus

Lysosomes

•  Recycling centers

– A kind of membrane-sealed acid vat that takes in large molecules, breaks them down, and returns what is usable to the cell

Lysosomes •  Digest:

– worn out cellular components, including whole organelles by membrane fusion

–  invading bacteria

– other foreign material

•  Contain many enzymes to perform these diverse chemical reactions

Mitochondria: Powerhouses

•  All these cellular processes require energy

•  Of course, energy comes from food

•  Mitochondria convert “food” to a universal currency for cellular energy: ATP

Mitochondria •  Power-hungry cells have hundreds; quiet cells

have only a few •  Mitochondria consume OXYGEN

and release HEAT and CO2

(that’s why you need to breathe!)

Mitochondria

•  Likely are remnants of ancient endosymbionts

(bacteria that lived inside other cells)

Mitochondria even have their own DNA!!

Cytoskeleton

•  Structural support •  Maintain cell shape

•  Cell movement

The Cytoskeleton Microfilaments Intermediate Filaments

Cytoskeleton: Microtubules Tube-shaped structures that form

Cilia Flagella

Structure

(cytoskeleton)

Control Center (nucleus)

Assembly Line (Endoplasmic Reticulum) Workbenches (ribosomes) Distribution center (Golgi complex)

Cleaning Crew (lysosomes)

Security Gate (cell membrane)