THE TOUR OF THE CELL CHAPTER 4 Cell

THE TOUR OF THE CELL CHAPTER 4

Cell Theory 1) Every organism is composed of one or more cells 2) Cell is smallest unit having properties of life (movement, respiration, sensitivity, growth, reproduction, excretion & nutrition). 3) All cells come from other cells.

Basic Aspects of Cell Structure & Function l The cell: • Smallest unit of life • Can survive on its own or has potential to do so • Is highly organized for metabolism • Senses and responds to environment • Has potential to reproduce

Structure of Cell All start out life with: • Plasma membrane • Region where DNA is stored • Cytoplasm Two types: • Prokaryotic • Eukaryotic

Fluid Mosaic Model of Cell Membrane (Phospholipid Bilayer) l Main component of cell membranes l Gives the membrane its fluid properties l Two layers of phospholipids

Phospholipid Bilayer

Fluid Mosaic Model l Membrane is a mosaic of l Most phospholipids and some proteins can drift through membrane • Phospholipids • Glycolipids • Sterols • Proteins

Fluid Mosaic Model EXTRACELLULAR ENVIRONMENT CYTOPLASM

Cell Size & Shape l Why Are Cells So Small? l Surface-to-volume ratio l The bigger a cell is, the less surface area there is per unit volume l Above a certain size, material cannot be moved in or out of cell fast enough

Defining Features of Eukaryotic Cells l l Have a nucleus and other membrane bound organelles Eukaryotic organisms • Plants • Animals • Protistans • Fungi

Animal Cell Features l l Plasma membrane Nucleus Ribosomes Endoplasmic reticulum l l Golgi body Vesicles Mitochondria Cytoskeleton

Animal Cell

Plant Cell Features l l l Plasma membrane Nucleus Ribosomes Endoplasmic reticulum Golgi body l l l Cell wall Chloroplast Central Vacuole Vesicles Mitochondria Cytoskeleton

The Nucleus l Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm l Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells

Components of Nucleus l l l Nuclear envelope Nucleoplasm Nucleolus Chromosome Chromatin

Nuclear Envelope l Two outer membranes (lipid bilayers) l Pores span bilayer

Nucleolus l l l Cluster of DNA and proteins Materials from which ribosomal subunits are built Subunits must pass through nuclear pores to reach cytoplasm

Chromatin l l l Cell’s collection of DNA and associated proteins Chromosome is one DNA molecule and its associated proteins Appearance changes as cell divides

The Endomembrane System l Group of related organelles in which lipids are assembled and new polypeptide chains are modified l Products are sorted and shipped to various destinations

Endoplasmic Reticulum (ER) l In animal cells, continuous with nuclear membrane l Extends throughout cytoplasm l Two regions - rough and smooth l Protein synthesis (RER), Lipid synthesis (SER)

Mitochondria l ATP-producing powerhouses l Double-membrane system l Carry out the most efficient energyreleasing reactions l These reactions require oxygen

Specialized Plant Organelles l Central Vacuole l Chloroplasts

Central Vacuole l Fluid-filled organelle l Stores amino acids, sugars, wastes l As cell grows, vacuole expands as a result of fluid pressure forces cell wall to expand l In mature cell, central vacuole takes up 50 -90 percent of cell interior

Chloroplasts Convert sunlight energy to ATP through photosynthesis

The Cytoskeleton l Present in all eukaryotic cells l Basis for cell shape and internal organization l Allows organelle movement within cells and, in some cases, cell movement

Components of Cytoskeleton intermediate filament microtubule microfilament

Mechanisms of Movement l Length of microtubules or microfilaments can change l Parallel rows of microtubules or microfilaments actively slide in a specific direction Microtubules or microfilaments can move organelles to different parts of cell l

Flagella and Cilia l Structures for cell Microtubule doublet motility l 9 + 2 internal structure Dynein arm

Cell Surface Specializations & Junctions l Cell wall • • Structural component that wraps around the plasma membrane Occurs in plants, some fungi, some protistans

Cell Junctions l Plants • Plasmodesmata l Animals • Tight junctions • Adhering junctions • Gap junctions

Animal Cell Junctions Tight junctions Adhering junction Gap junction

Prokaryotic Cells l Archaebacteria and Eubacteria l DNA is NOT enclosed in nucleus l Generally the smallest, simplest cells l No organelles