copyright © 2004 pearson education, inc. publishing as benjamin cummings cell size is limited...

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

Cell Size is Limited• Surface to Volume Ratio limits upper size

• Larger cells have less surface area relative to volume


A Generic Animal Cell


• An idealized plant cell

Cell Membrane

Function

1. Separates cytoplasm from external environment

2. Regulates what enters and leaves cell

3. Cell identification

4. Cell-cell communication

Plasma membrane regulates movement of

materials due to its chemical

composition:Phospholipids

CholesterolProteins

Phospholipids

• Phospholipids BilayerPhospholipids have:1. Hydrophilic head

2.Nonpolar hydrophobic tail

Hydrophilic "heads" faces the watery environment inside and outside cell

Hydrophobic tail forced to face inward – away from water.

The phospholipids are

not bound together –

gives the membrane a

fluid nature

CHOLESTEROL

• Function:

1.Stabilizes membrane (structural support)

2.Cell communication (cell-cell and cell-hormone)

Some interesting facts

• Most common molecule in membrane (>50%)

• Due small size and weight – only 20% of membrane mass

• Is an amphipathic molecule Homework – find out what this means

Proteins

• Are embedded in membrane

• Serve different functions

Functions

• 1. Channel Proteins - small openings for molecules to diffuse through

• 2. Carrier Proteins- binding site on protein "grabs” molecules, pulls them into cell

• 3. Receptor Proteins – act as triggers that set off cell responses (such as release of hormones or opening of channel proteins)

• 4. Cell Recognition Proteins - ID tags, identify cell to immune system

• 5. Enzymatic Proteins - carry out metabolic reactions

LABEL YOUR DIAGRAM WITH THE FOLLOWING

DETAILS

Task: Due Tuesday Oct. 4,

2011• Read pages 47 -49 in your text

• Answer questions 1 – 5 in practice section

• Explain the structure and function of glycoproteins.

• How are liposomes used in cancer treatment and gene therapy?

• What role might receptor proteins have in medical disorders such as Hypertension?


• Surrounded by a double membrane called the nuclear envelope

Structure and Function of the Nucleus

– It contains

– chromatin -a DNA-protein structure

– a nucleolus - which produces ribosomal parts

– Nucleoplasm

• Occurs only in eukaryotic cells


• Animation of nuclear membrane system

• http://users.uma.maine.edu/SBaker/nucleus_endo.html

• Animation of nuclear membrane system

• http://users.uma.maine.edu/SBaker/nucleus_endo.html


Nuclear Pore Complex

Allows movement of material into and out of nucleus


• Ribosomes build all the cell’s proteins

– Are not membrane bound

Ribosomes


• DNA controls the cell by transferring its coded information into RNA

How DNA Controls the Cell

– The information in the RNA is used to make proteins

Synthesis ofmRNA in thenucleus

1

2 Movement ofmRNA intocytoplasm vianuclear pore

3 Synthesis ofprotein in thecytoplasm

DNA

mRNA

Nucleus

Cytoplasm

mRNA

Ribosome

Protein


• Many of the membranous organelles in the cell belong to the endomembrane system

– Endoplasmic reticulum - rough and smooth

– Golgi Apparatus

– Lysosomes

– Vacuoles

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING

CELLULAR PRODUCTS


• The endoplasmic reticulum (ER)

The Endoplasmic Reticulum

– Greek for ‘network within a cell’

– Produces an enormous variety of molecules

– Is composed of smooth and rough ER

Nuclearenvelope

Ribosomes

Rough ERSmooth ER


• The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

Rough ER


• The functions of the rough ER include

– Producing proteins

– Producing new membrane


• After the rough ER synthesizes a molecule it packages the molecule into transport vesicles

1


Smooth ER• The smooth ER lacks

the surface ribosomes of ER

• Produces lipids, including steroids and sex hormones

• Regulates sugar

• Detoxifies drugs

• Stores calcium


• The Golgi apparatus

The Golgi Apparatus

– Works in partnership with the ER

– Refines, stores, and distributes the products of cells

Transportvesiclefrom ER

“Receiving” side ofGolgi apparatus

Golgi apparatus

New vesicle forming

Transport vesiclefrom the Golgi

“Shipping” side ofGolgi apparatus

Plasma membrane


• A lysosome is a membrane-enclosed sac

Lysosomes

– Greek for ‘breakdown body’

– It contains digestive enzymes

• Isolated by membrane

– The enzymes break down

• Macromolecules

• Old organelles


• Lysosomes have several types of digestive functions

• They exit the Golgi apparatus


– They fuse with food vacuoles to digest the food


– They fuse with old organelles to recycle parts

– Digest bacteria in white blood cells


Lysosomal diseasesGenetic disorders

Recipe is messed up

Enzyme doesn’t work

what should get broken down doesn’t

Tay-Sachs

lipids aren’t broken down

build up occurs

death by age 5

Pompe’s disease

glycogen builds up


• Vacuoles are membranous sacs

Vacuoles

– Two types are the contractile vacuoles of protists and the central vacuoles of plants

Figure 4.15

Contractilevacuoles

Centralvacuole

(a) Contractile vacuoles in a protist (b) Central vacuole in a plant cell


• A review of the endomembrane system


• Cells require a constant energy supply to do all the work of life

CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION


• Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy

CHLOROPLASTS

Figure 4.17

Inner and outermembranes ofenvelope

Space betweenmembranes

Stroma (fluid inchloroplast)

Granum


Chloroplasts• Double membrane

• Grana

– Stacks of thylakoids

• Hollow disks

• Sunlight energy is coverted to chemical energy

• Stroma- fluid filling chloroplast

• Contains some DNA


• Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules

Mitochondria

Figure 4.18

Outermembrane

Innermembrane

Cristae

Matrix

Space betweenmembranes


Mitochondria• Double membrane

– Big bag stuffed into smaller bag

– Folds of inner bag called cristae

• Matrix -space inside inner bag

• Contains some DNA


• The cytoskeleton is an infrastructure of the cell consisting of a network of fibers

– Microfilaments - small threads

– Intermediate filaments - ropelike

– Microtubules - small tubes

THE CYTOSKELETON:CELL SHAPE AND MOVEMENT


• One function of the cytoskeleton

Maintaining Cell Shape

– Provide mechanical support to the cell and maintain its shape


Figure4.9x


• The cytoskeleton can change the shape of a cell

– This allows cells like amoebae to move


• Cilia and flagella are motile appendages

Cilia and Flagella


• Flagella propel the cell in a whiplike motion

• Cilia move in a coordinated back-and-forth motion

Figure 4.20A, B


• Some cilia or flagella extend from nonmoving cells

– The human windpipe is lined with cilia

– Smoking damages the cilia


Cilia and Flagella

• Same structure and function

• 9 + 2 arrangement of microtubules

• Wrapped in plasma membrane


Mechanism of Movement• Dynein arms use ATP for energy to ‘walk’ up adjoining

microtubule, causing them to bend


• Most cells secrete materials that are external to the plasma membrane

• This extra cellular matrix

– Regulates

– Protects

– Supports

CELL SURFACES:PROTECTION, SUPPORT, AND CELL-CELL

INTERACTIONS


• Plant cells are encased by cell walls

Plant Cell Walls and Cell Junctions

Figure 4.21

– These provide support for the plant cells

Walls of two adjacentplant cells

Vacuole

Plasmodesmata(channels between cells)


• Animal cells lack cell walls

Animal Cell Surfaces and Cell Junctions

– They secrete a sticky covering called the extracellular matrix

– This layer helps hold cells together


• Animal cells connect by various types of junctions

– Tight junctions – leakproof – fuses membranes of cells – found in intestinal epithelium (lining of intestine). Made of filaments (type of cytoskeleton material made from glycoprotein)

– Anchoring junctions - Desmosomes - hold cells together

– Communicating junctions - gap junctions. Provides a channel between cells for passage of small ions and molecules. Gap junctions are found in embryos, cardiac muscles and endocrine glands


Figure 4.22

Extracellular matrix

(a) Tight junctions

(b) Anchoring junctions

(c) Communicating junctions

Plasma membranesof adjacent cells

Extracellular matrix

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