Cell Structure and Function
Chapter 4
4.1 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
Fig. 4.4, p. 53
one layerof lipidsone layerof lipids
membraneprotein
extracellularenvironment
cytoplasm
Cell Size and Shape
Surface-to-volume ratio limits cell size
4.2 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
Microscopes
Different microscopes use light or electrons to reveal details of cell shapes or structures
Five Different Views
4.3 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, sterols,
proteins, and other components• Phospholipids drift within the bilayer
Many proteins are embedded in or attached to cell membrane surfaces• Receptors, transporters, communication proteins, and
adhesion proteins Plasma (outer) membrane also incorporates recognition
(marker) proteinsAnimation: http://www.susanahalpine.com/anim/Life/memb.htm
Common Membrane Proteins
Membrane Structure Studies
4.4 Introducing Prokaryotic Cells
Bacteria and archaeans• The simplest cells• The groups with greatest metabolic diversity
Cell wall• Surrounds plasma membrane in nearly all prokaryotic organisms
Flagella• Used for motion by prokaryotes that are motile
Capsule• Protects cells from immune destruction
Pili• Protein filaments in some that are used for attachment to
surfaces• “Sex” pilus transfers genetic material
Prokaryote Structure
Prokaryote Structure
4.6 Introducing Eukaryotic Cells
Start with a nucleus and other organelles• Carry out specialized functions inside a cell
Components of Eukaryotic Cells
4.7 Components of The Nucleus
Nucleus separates DNA from cytoplasm• Chromatin (all chromosomal DNA with proteins)
• Chromosomes (condensed)
Nucleolus assembles ribosome subunits
Nuclear envelope encloses nucleoplasm• Pores, receptors, transport proteins
Organization of DNAImage from: http://micro.magnet.fsu.edu/cells/nucleus/images/chromatinstructurefigure1.jpg
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
4.8 The Endomembrane System
Endoplasmic reticulum (ER) • An extension of the nuclear envelope• RER modifies new polypeptide chains• SER makes lipids; other metabolic functions
Transport vesicles• used to move proteins through the cytoplasm
Golgi bodies • Further modify polypeptides• Assemble lipids
Plasma membrane• Where transport vesicles attach to “secrete” cell
products
Endomembrane System Image From: http://www.phschool.com/science/biology_place/biocoach/images/cells/Endosyst.jpg
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
4.9 Mitochondria and Chloroplasts
Mitochondria • Break down organic compounds by aerobic
respiration (oxygen-requiring)
• Produce ATP
Chloroplasts• Produce sugars by photosynthesis
Origins of mitochondria and chloroplasts:http://www.sumanasinc.com/webcontent/animations/content/organelles.html
Mitochondria image from:http://pingrybiology.pbworks.com/f/p0014498-mitochondria.gif
Chloroplasts
4.10 Visual Summary: Plant Cells
Visual Summary: Animal Cells
4.11 Cell Surface Specializations
Most prokaryotes, protists, fungi, all plant cells have a cell wall around their plasma membrane• Protects, supports, maintains cell shape
• Primary and secondary cell walls in some plants
Plasmodesmata across cell walls connect plant cells
Plant Cell Walls
Plant Cell Walls
Plant Cuticle
Protective surface secretion, limits water loss
Extracellular Matrixes
Surrounds cells of specific tissues – • some are hard (bone) and some are liquid (blood)
Animal Cell Junctions
Connect cells of animals• Adhering junctions, tight junctions, gap junctions
4.12 The Dynamic Cytoskeleton
Components of the cytoskeleton• Microtubules
• Microfilaments
• Intermediate filaments (in most)
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/organism
Paramecium image from: http://www.zeiss.de/C12567BE00472A5C/GraphikTitelIntern/Parameciumgross/$File/paramecium1.jpg
Motor Protein: Kinesin
Moves vesicles along microtubules• Animation: http://www.susanahalpine.com/anim/Life/kinesin.htm
Flagellum and Pseudopods
Eukaryotic Flagella and Cilia: Dynein
Eukaryotic Flagella and Cilia: Dynein
Microtubule organizing center
Responsible for the organization/formation of microtubules that function during cell division• Contain centrioles in animal cells