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 pilus plasma membrane DNA in nucleoid cytoplasm, with ribosomes Most prokaryotic cells have a cell wall outside the plasma membrane, and many have a thick, jellylike capsule around the wall. cell wall capsule

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

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

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