Chapter 7 Inside the Cell Biological Science, Third Edition – Scott Freeman Lectures by Cheryl Ingram-Smith

What’s a Cell? The cell is the simplest collection of matter that can be alive Looking at cell structure, there are two broad groupings of life: Prokaryotes, which lack a membrane-bound nucleus. Eukaryotes, which have such a nucleus. For the Discovery Channel Video Cells, go to Animation and Video Files

Prokaryotic Cells . Prokaryotic cells generally have few or no substructures separated from the rest of the cell by internal membranes. Along with a membrane, Prokaryotes have a tough cell wall that protects the cells and gives them shape and structure.

A Prokaryotic Cell Ribosomes Plasmids Cytoplasm Chromosome Flagellum Plasma membrane Cell wall

Eukaryotes and Prokaryotes Compared Major differences between typical eukaryotes and prokaryotes are as follows: (1) Eukaryotic chromosomes are found inside a membrane- bound compartment called a nucleus. (2) Eukaryotic cells are often much larger. (3) Eukaryotic cells contain extensive amounts of internal membrane. (4) Eukaryotic cells feature a diverse and dynamic cytoskeleton.

Eukaryotic Cells The relatively large size of the eukaryotic cell makes it difficult for molecules to diffuse across the entire cell. Organelles help solve this problem by breaking up the large cell volume into several smaller functional units. chemical reaction efficiency by separating incompatible chemical reactions and grouping enzymes and substrates together. The quantity/size of organelles is determined by the function of the cell, but all eukaryotic cells share some common features. For the Cell Biology Video Movement of Organelles in Vitro, go to Animation and Video Files For the Cell Biology Video Movement of Organelles in Vivo, go to Animation and Video Files

Animal and Plant Cells Generalized animal cell Nuclear envelope Nucleolus Nucleus Chromosomes Rough endoplasmic reticulum Centrioles Ribosomes Peroxisome Structures that occur in animal cells but not plant cells Smooth endoplasmic reticulum Golgi apparatus Lysosome Mitochondrion Cytoskeletal element Plasma membrane

Animal and Plant Cells Generalized plant cell Nuclear envelope Nucleolus Nucleus Chromosomes Rough endoplasmic reticulum Structures that occur in plant cells but not animal cells Ribosomes Smooth endoplasmic reticulum Golgi apparatus Cell wall Vacuole (lysosome) Chloroplast Peroxisome Mitochondrion Plasma membrane Cytoskeletal element On average, prokaryotes are about 10 times smaller than eukaryotic cells in diameter and about 1000 times smaller than eukaryotic cells in volume.

The Nucleus It houses the cell’s genetic material (DNA) Directs protein synthesis by synthesizing mRNA contains most of the cell’s genes and is usually the most conspicuous organelle Enclosed by the nuclear envelope, separating it from the cytoplasm

Close-up of nuclear envelope Chromatin Nucleus Nucleolus Chromatin Figure 4.8a Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Figure 4.8a The nucleus and its envelope (part 1: detail of art) Pore complex Ribosome Close-up of nuclear envelope Chromatin 10

Ribosomes The protein factory of the cell Composed of complexes of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations In the cytosol (free ribosomes)-make Proteins used in the cell On the outside of the endoplasmic reticulum (bound ribosomes)-make Proteins for the membrane or export

Free ribosomes in cytosol Figure 4.9 0.25 m Ribosomes ER Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit Figure 4.9 Ribosomes Small subunit TEM showing ER and ribosomes Diagram of a ribosome 12

Endomembrane System Components of the endomembrane system Nuclear envelope Endoplasmic reticulum (smooth and rough) Golgi apparatus Lysosomes Vacuoles Plasma membrane These components are either continuous or connected through transfer by vesicles

Endoplasmic Reticulum Accounts for more than half of the total membrane volume in many eukaryotic cells Continuous with the nuclear envelope Two distinct regions of ER Smooth ER: lacks ribosomes Rough ER: surface is studded with ribosomes

Functions of Smooth ER Synthesizes lipids—such as hormones Detoxifies drugs and poisons—by adding hydroxyl, making molecule more soluble. Stores calcium ions—drives muscle cell contraction © 2014 Pearson Education, Inc. 15

Functions of Rough ER bound ribosomes, secrete glycoproteins used for cell signaling Distributes transport vesicles, proteins surrounded by membranes Most proteins synthesized in rough ER are bound for membranes or excretion from cell Is the membrane factory for the cell © 2014 Pearson Education, Inc. 16

Endoplasmic Reticulum Transport vesicle Smooth ER Rough ER Ribosomes Transitional Cisternae ER lumen Rough ER Nuclear envelope 0.2 m

Golgi Apparatus Consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles Can be thought of as the warehouse of the cell. Stores & coordinates the transport of materials made by the cell.

Golgi Apparatus Golgi apparatus 0.1 m cis face (“receiving” side of TEM of Golgi apparatus Golgi apparatus trans face (“shipping” side of Golgi apparatus) Cisternae 0.1 m cis face (“receiving” side of Golgi apparatus)

Lysosomes Membranous sac of hydrolytic enzymes that digest macromolecules for energy Creates an acidic environment for enzymes to digest food Can fuses with the food vacuole and digests the molecules Also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy

Lysosomes 1 m Nucleus Lysosome Digestive enzymes Plasma membrane Food vacuole Lysosomes: Phagocytosis Digestion

Vacuole Large vesicles derived from the endoplasmic reticulum and Golgi apparatus Food vacuoles are formed by phagocytosis Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many plant cells, hold organic compounds and water (storage)

Vesicles

Energy Organelles Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP Chloroplasts, found in plants and algae, are the sites of photosynthesis Both contain their own DNA, separate from the DNA in the Nucleus!

Energy Organelles

Endosymbiont Theory An early ancestor of eukaryotic cells engulfed a prokaryotic cell The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion Some then engulfed a photosynthetic prokaryote, creating the early ancestors of plants and alage

Endosymbiont Theory Mitochondrion Nonphotosynthetic eukaryote At least one cell Chloroplast Engulfing of photosynthetic prokaryote Nucleus Nuclear envelope Endoplasmic reticulum Ancestor of eukaryotic cells (host cell) Engulfing of oxygen- using nonphotosynthetic prokaryote, which becomes a mitochondrion

Cytoskeleton The cytoskeleton is a network of fibers extending throughout the cytoplasm It organizes the cell’s structures and activities, anchoring many organelles

Cytoskeleton The cytoskeleton helps to support the cell and maintain its shape It interacts with motor proteins to produce motility Inside the cell, vesicles and other organelles can “walk” along the tracks provided by the cytoskeleton (b) SEM of a squid giant axon Receptor for motor protein Vesicle Motor protein (ATP powered) ATP Microtubule of cytoskeleton Motor proteins “walk” vesicles along cytoskeletal fibers.

Cytoskeleton Three main types of fibers make up the cytoskeleton Microtubules (thickest) Shape and support the cell Guide movement of organelles Separate chromosomes during cell division Microfilaments (thinnest) bear tension, resisting pulling forces Create movement & shape changes of cell Initiates cell division Intermediate filaments Anchors organelles within cell

Cytoskeleton