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

bacterial flagellum

pilusplasma membrane

DNA in nucleoid

cytoplasm, with ribosomes

Most prokaryotic cells have a cellwall outside the plasma membrane,and many have a thick, jellylikecapsule around the wall. cell

wallcapsule

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