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

extracellular environment one layer of lipids one layer of lipids membrane protein cytoplasm Fig. 4.4, p. 53

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) proteins Animation: 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 DNA Image from: http://micro. magnet. fsu

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

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 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

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