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