Cell Structure and Function
What is a Cell?
 Each cell has a plasma membrane, cytoplasm,
and a nucleus (in eukaryotic cells) or a nucleoid (in
prokaryotic cells)
Components of Cell Membranes
 Lipid bilayer
Cell Size and Shape
 Surface-to-volume ratio limits cell size
Key Concepts:
WHAT ALL CELLS HAVE IN COMMON
 Each cell has a plasma membrane, a boundary
between its interior and the outside environment
 The interior consists of cytoplasm and an
innermost region of DNA
How Do We See Cells?
 Three key points of the cell theory:
• All organisms consist of one or more cells
• The cell is the smallest unit that retains the
capacity for life
• A cell arises from the growth and division of
another cell
Relative Sizes
Membrane Structure and Function
 Each cell membrane is a boundary (lipid bilayer)
that controls the flow of substances across it
 Fluid mosaic model
• Membrane is composed of phospholipids,
cholesterol, proteins, and other components
• Phospholipids drift within the bilayer
Common Membrane Proteins
Introducing Prokaryotic Cells
 Bacteria and archaeans
• The simplest cells
• The groups with greatest metabolic diversity
Prokaryote Structure
 Cell wall
• Surrounds plasma membrane
 Flagella
• Used for motion
 Pili
• Protein filaments used for attachment
• “Sex” pilus transfers genetic material
cytoplasm,
with ribosomes
bacterial flagellum
Most prokaryotic cells have a cell
wall outside the plasma membrane,
and many have a thick, jellylike
capsule around the wall.
DNA in
cell plasma
pilus capsule wall membrane nucleoid
Introducing Eukaryotic Cells
 Start with a nucleus and other organelles
• Carry out specialized functions inside a cell
Components of The Nucleus
 Nucleus separates DNA from cytoplasm
• Chromatin (all chromosomal DNA with proteins)
• Chromosomes (condensed)
 Nucleolus assembles ribosome subunits
 Nuclear envelope and Pores
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
The Endomembrane System
 Endoplasmic reticulum (ER)
• An extension of the nuclear envelope
• RER modifies new polypeptide chains
• SER makes lipids; other metabolic functions
 Golgi bodies
• Further modify polypeptides
• Assemble lipids
The Endomembrane System
 Vesicles
• Endocytic and exocytic: Transport or store
polypeptides and lipids
• Peroxisomes: Digest fatty acids and amino acids;
break down toxins and metabolic by-products
• Lysosomes: Intracellular digestion (animals)
• Central vacuole: Storage; fluid pressure (plants)
Endomembrane System
Endomembrane System
Endomembrane System
Mitochondria and Chloroplasts
 Mitochondria
• Break down organic compounds by aerobic
respiration (oxygen-requiring)
• Produce ATP
 Chloroplasts
• Produce sugars by photosynthesis
Mitochondria and Chloroplasts
The Dynamic Cytoskeleton
 Components of the cytoskeleton
• Microtubules
• Microfilaments
• Intermediate filaments
Components of the Cytoskeleton
Cytoskeleton Function
 Organizes and moves cell parts
 Reinforces cell shape
 Interactions between motor proteins and
microtubules in cilia, flagella, and pseudopods
can move the whole cell
Flagellum and Pseudopods