Chapter 6 Part B A tour of The Cell

Smooth ER & its Functions It lacks the surface ribosomes Its functions include: Synthesizes lipids Metabolizes carbohydrates Stores calcium Detoxifies poison

The Golgi Apparatus The Golgi apparatus Consists of flattened membranous sacs called cisternae Works in partnership with the ER. Receives many of the transport vesicles produced in the rough ER Refines, stores, and distributes the chemical products of the cell.

Figure 4.12

Functions of the Golgi apparatus cis face (“receiving” side of Golgi apparatus) Vesicles move from ER to Golgi Vesicles also transport certain proteins back to ER Vesicles coalesce to form new cis Golgi cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma mem- brane for secretion Vesicles transport specific proteins backward to newer Cisternae trans face (“shipping” side of 0.1 0 µm 1 6 5 2 3 4 Golgi apparatus Figure 6.13 TEM of Golgi apparatus

A lysosome is a membrane-enclosed sac. Lysosomes A lysosome is a membrane-enclosed sac. It contains digestive enzymes. The enzymes break down macromolecules. Lysosomes have several types of functions:

They fuse with food vacuoles to digest the food. digestive Lysosome Formation

They break down damaged organelles.

Vacuoles are membranous sacs. Two types: the contractile vacuoles of protists the central vacuoles of plants.

Figure 4.14

A review of the endomembrane system

Chloroplasts and Mitochondria: Both energy transformers with two membranes Mitochondria (two membranes) Found in nearly all eukaryotes Are the sites of cellular respiration Chloroplasts (two membranes) Found only in plants Member of the plasid family Contain chlorophyl Sites of photosynthesis

Chloroplasts and Mitochondria: Energy Conversion Cells require a constant energy supply Chloroplasts: The sites of photosynthesis, which is: the Conversion of light energy to chemical energy Mitochondria: The sites of cellular respiration, which involves: the production of ATP from food molecules. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Chloroplast structure includes Thylakoids, membranous sacs Stroma, the internal fluid

Are found in leaves and other green organs of plants and in algae Chloroplasts Are found in leaves and other green organs of plants and in algae Chloroplast DNA Ribosomes Stroma Inner and outer membranes Thylakoid 1 µm Granum Figure 6.18

Mitochondria are enclosed by two membranes A smooth outer membrane An inner membrane folded into cristae Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Mitochondrial DNA Inner Cristae Matrix 100 µm Figure 6.17

Mitochondria and chloroplasts share another feature unique among eukaryotic organelles. They contain their own DNA. They contain their own ribosomes The existence of separate “mini-genomes” is believed to be evidence that Mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past.

Peroxisomes: Oxidation Produce hydrogen peroxide and convert it to water Chloroplast Peroxisome Mitochondrion 1 µm Figure 6.19

A cellular infrastructure of a network of fibers. The Cytoskeleton: A cellular infrastructure of a network of fibers. Provides mechanical support to the cell Maintain the shape of the cell Forms tract for organelles movement Can change the shape of a cell allowing cells like amoebae to move. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Cytoskeleton Three main types of fibers making the cytoskeleton: Microtubules: Shape the cell & guide movement of organelles Help separate chromosome in dividing cells Intermediate filaments: Support cell shape Fix organelles in place Microfilaments Made of actin and involved in motility

Figure 4.18a

Centrosomes and Centrioles The centrosome Is considered to be a “microtubule-organizing center”

Contains a pair of centrioles Centrosome Microtubule Centrioles 0.25 µm Longitudinal section of one centriole Microtubules Cross section of the other centriole Figure 6.22

Cilia and Flagella Cilia and flagella are motile appendages. Flagella propel the cell in a whiplike motion. Cilia move in a coordinated back-and-forth motion.

Figure 4.19a, b

Some cilia or flagella extend from nonmoving cells. The human windpipe is lined with cilia.

The Extracellular Matris (ECM) made up of glycoproteins and other macromolecules Collagen Fibronectin Plasma membrane EXTRACELLULAR FLUID Micro- filaments CYTOPLASM Integrins Polysaccharide molecule Carbo- hydrates Proteoglycan Core protein Integrin Figure 6.29 A proteoglycan complex

Functions of the ECM include Support Adhesion Movement Regulation

Intercellular Junctions Plant Plasmodesmata Are channels that perforate plant cell walls Interior of cell 0.5 µm Plasmodesmata Plasma membranes Cell walls Figure 6.30

Animals: Tight Junctions, Desmosomes, and Gap Junctions In animals, there are three types of intercellular junctions Tight junctions Desmosomes Gap junctions

Types of intercellular junctions in animals Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm 1 µm Space between cells Plasma membranes of adjacent cells Extracellular matrix Gap junction Tight junctions 0.1 µm Intermediate filaments Desmosome Gap junctions At tight junctions, the membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins (purple). Forming continu- ous seals around the cells, tight junctions prevent leakage of extracellular fluid across A layer of epithelial cells. Desmosomes (also called anchoring junctions) function like rivets, fastening cells Together into strong sheets. Intermediate Filaments made of sturdy keratin proteins Anchor desmosomes in the cytoplasm. Gap junctions (also called communicating junctions) provide cytoplasmic channels from one cell to an adjacent cell. Gap junctions consist of special membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for commu- nication between cells in many types of tissues, including heart muscle and animal embryos. TIGHT JUNCTIONS DESMOSOMES GAP JUNCTIONS Figure 6.31