Chapter 4

Structure and Function of Cells

Cells are the basic units of life

All organisms are composed of cells

• Cell theory states– A cell is the basic unit of life– All living things are made up of cells– New cells arise only from preexisting cells

Metabolically active cells are small in size

Why are cells so small?Cells need a surface area large enough to gain nutrients and get rid of waste.

Prokaryotic cells evolved first

• Prokaryotic (“before” “nucleus”) cells lack a membrane bound nucleus

• Prokaryotic cells are also much smaller than eukaryotic• Domains Bacteria and Archaea are prokaryotic• All cells contain

– Cell membrane (plasma membrane)– Cytoplasm– Genetic material

• Prokaryotic cells contain– Cell membrane

• Allows substances in and out

– Cytoplasm• Fluid that fills cell

– Ribosomes• Protein synthesis

– Cell wall• Holds cell shape

– Pili• Allows attachment to solid

surfaces

– Flagella (some cells)• movement

Prokaryotic cells cause disease, decompose dead material, and are used in the production of food and drugs.

Eukaryotic cells contain specialized organelles

• Eukaryotic (“true” “nucleus”) cells have a membrane bound nucleus

• Domain Eukarya contains eukaryotic cells• Larger than prokaryotic cells• Less surface area to volume• Contains organelles (“little organs”) that perform specific

functions

Animal Cell

Plant Cell – Notice the cell wall, chloroplasts, and large central vacuole

Protein synthesis is a major function of cells

The nucleus contains the cell’s genetic information• Chromosomes

– DNA and proteins

• Chromatin– Extended chromosomes after cell division

• Nucleolus– Region of chromatin where subunits of ribosomes are produced

• Nuclear envelope– Separates nucleus from cytoplasm

• Nuclear pores– Allows ribosomal subunits out and proteins in

The ribosomes carry out protein synthesis

• Do not have membranes• Polyribosomes

– Group of ribosomes

• Endoplasmic reticulum– Rough version has ribosomes attached to it

• Messenger RNA– Copy of a gene– Tells cell how to make a particular protein– Indicates correct sequence of amino acids– Leaves nucleus via nuclear pore– Attaches to ribosome– Protein is produced

The endoplasmic reticulum synthesizes and transports proteins and lipids

• Many ribosomes attach to the endoplasmic reticulum, making it a site of protein production

• Types of ER– Rough ER

• Has ribosomes attached• Make proteins

– Smooth ER• Does not have ribosomes attached• Make lipids

• Transport vesicles– Pinched off portions of ER that contain proteins,

membranes, and lipids going mainly to the Golgi apparatus

The Golgi apparatus modified and repackages proteins for distribution

• Receives, processes, and packages proteins and lipids, so that they may be sent to their final destination

• Receives at inner face• Processes as it moves from inner face to outer face• Packages into vesicles that leave from the outer face

– Some are secretory vesicles that discharge contents out of the cell. Also called exocytosis.

Vacuoles and vesicles have varied functions

Lysosomes digest biomolecules and cell parts

• Vesicles produced by Golgi apparatus

• Have low internal pH that digests old and worn-out organelles

• White blood cells engulf bacteria and digest it to protect your body

Peroxisomes break down long-chain fatty acids

• Help produce cholesterol and important phospholipids

• In germinating seeds, convert fatty acids and lipids to sugars that are used as energy

Vacuoles are common to plant cells

• Store water, sugars, salts, toxins (protects plant from herbivory), and water-soluble pigments (responsible for flower color)

• Central vacuole provides support to the plant

• Stores waste and breaks down old organelles like lysosomes in animal cells

Vesicles allow the organelles of the endomembrane system to work together

1. Proteins, produced in the rough ER are carried in

2. Transport vesicles to

3. The Golgi apparatus, which sorts the proteins and packages them into vesicles that transport them to various cellular destinations

4. Secretory vesicles take proteins to the plasma membrane, where they exit the cell when the vesicles fuse with the membrane

5. In animal cells, lysosomes produced by the Golgi apparatus

6. Fuse with incoming vesicles from the plasma membrane and digest biomolecules and debris

A cell carries out energy transformations

Chloroplasts and mitochondria have opposite functions

• Chloroplasts are found in plant cells and contain the green pigment chlorophyll, which is responsible for the ability to absorb solar energy

• Protists and algae also contain chloroplasts• Mitochondria carry out cellular respiration• Mitochondria produce ATP

(Cellular respiration and photosynthesis reactions)

The cytoskeleton is dynamicThe cytoskeleton maintains cell shape and assists movement• Cytoskeleton

– Network of protein fibers within cytoplasm– Holds organelles in place but allows them to move if needed– Allows cells to change shape– Support and movement

• Types of fibers– Actin filaments

• Support plasma membrane• Largest

– Intermediate filaments• Support nuclear envelope, plasma membrane, and cell to cell connections• Medium

– Microtubules• Maintain shape of cell and act as tracks along which organelles can move• Smallest

Cilia and flagella permit movement

• Cilia– Short– Move an egg along the oviduct– Move mucus that contains debris out of lungs

• Flagella– Long tail– Sperm tail