Cell Structure and Organelle Function

What Is the Cell Theory?

Why are cells small?

Cheek cells. microscopyu.com

All Cells Share Common Features

• Members of Bacteria, Eukaryota, and Archaea share common cellular features.

Plasma Membrane• A plasma membrane encloses all cells and

regulates material flow

Cytoplasm

• Cytoplasm – Interior fluid – Where cell’s metabolic reactions occur– Contains organelles– Fluid portion (cytosol) contains water, salts,

and organic molecules

Genetic Material

• All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint

• All cells use RNA (ribonucleic acid) to copy DNA to make proteins

All Cells Share Common Features

• All cells obtain energy and nutrients from the environment

• All cells use common building blocks to build the molecules of life

There Are Two Basic Cell Types• Cells are either:

– Prokaryotic• Before nucleus

– Eukaryotic• True nucleus• Membrane bound organelles www.ucmp.berkeley.edu/

alllife/eukaryota.html

Eukaryotic Cells

• Eukaryotic cells > 10 µm long

• Have membrane-enclosed organelles that perform specific functions

Cell Walls

The Cytoskeleton

The Cytoskeleton

• Main functions of cytoskeleton– Maintaining and changing cell shape– Providing for cell movement– Providing for organelle movement, including

vesicle endo- and exocytosis– Facilitating cell division in chromosome

movements and cytokinesis

Cilia and Flagella

• Cilia and flagella are extensions of the plasma membrane

• Cilia– Short, hair-like structures, numerous

• Flagella– Longer, whip-like, fewer in number

• Functions– motility– Cilia - create currents of moving fluid in

environment

The Nucleus• Control center of cell

• Contains genetic information (in eukaryotes)

• Contains:– Nuclear envelope– Chromosomes– Nucleolus

System of Membranes

• Membrane system includes the plasma membrane and organelle membranes

Vesicles

• Vesicles – membranous sacs that carry substances

throughout the cell

Endoplasmic Reticulum

• A series of enclosed, interconnected channels within cell

• Two forms of ER– Smooth ER

– Rough ER

Golgi Apparatus

• a set of stacked flattened sacs

Fate of Substances Made in the Membrane System (3)

1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane

Fate of Substances Made in the Membrane System (3)

2. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell• Lysosomes fuse

with food vacuoles and digest food into basic nutrients

Fate of Substances Made in the Membrane System (3)

3. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes

Vacuoles Serve Many Functions

• Fluid-filled sacs with a single membrane

• Contractile vacuoles in freshwater organisms used to collect and pump water out

Vacuoles Serve Many Functions

• Plant central vacuoles used in several ways• Maintain water balance• Store hazardous

wastes, nutrients, or pigments

• Provide turgor pressure on cytoplasm to keep cells rigid

Mitochondria Extract Food Energy

• Mitochondria - round, oval, or tubular sacs of double-membranes

– Inner membrane is folded into cristae

– Intermembrane compartment lies between inner and outer membranes

– Matrix space within inner membrane

Mitochondria Extract Food Energy

• Mitochondria may be remnants of free-living prokaryotes (endosymbiotic hypothesis)

thebrain.mcgill.ca

Plants Use Plastids for Storage

• Plastids found only in plants and photosynthetic protists

– Ex. chloroplasts

• Surrounded by a double membrane

• Functions– Storage for photosynthetic products– Storage of pigment molecules

Chloroplasts

• Chloroplasts - specialized organelles surrounded by a double membrane

– Outer membrane

– Inner membrane encloses the stroma space• Stacked hollow membranous sacs (grana)

within stroma are called thylakoids

Chloroplasts

• Contain chlorophyll and other pigments that capture sunlight, CO2, and water and are used to make sugar (photosynthesis)

Prokaryotic Cells

• Most prokaryotic cells (bacteria) are < 5 µm long

Prokaryotic Cell Wall

• A stiff cell wall is usually present

Prokaryotic Cells• Motility by flagella

• May have capsules or slime layers on their surfaces

• Pili and fimbriae are protein projections in some bacteria that further enhance adhesion

E. Coli with fimbriae. mgm.stonybrook.edu

E. Coli with fimbriae. med.upenn.edu

Prokaryotic Cells

• Cell shapes: bacilli, cocci, or spirilla

abe.ufl.edu

Prokaryotic Cells• Single, circular chromosome of DNA in

area called the nucleoid• Small rings of DNA (plasmids) located in

the cytoplasm

Prokaryotic Cells• No nuclear

membrane or membrane-bound organelles present

• Some have internal membranes used to capture light

• Cytoplasm may contain food granules

The End