enduring understanding 2.b growth, reproduction and dynamic homeostasis require that cells create...

E N D U R I N G U N D E R S TA N D I N G 2 . BG R O W T H , R E P R O D U C T I O N A N D D Y N A M I C

H O M E O S TA S I S R E Q U I R E T H AT C E L L S C R E AT E A N D M A I N TA I N

I N T E R N A L E N V I R O N M E N T S T H AT A R E D I F F E R E N T F R O M T H E I R E X T E R N A L

E N V I R O N M E N T S .

E S S E N T I A L K N O W L E D G E 2 . B . 3E U K A R Y O T I C C E L L S M A I N TA I N I N T E R N A L

M E M B R A N E S T H AT PA R T I T I O N T H E C E L L I N T O S P E C I A L I Z E D

R E G I O N S .

BIG IDEA IIBIOLOGICAL SYSTEMS UTILIZE FREE ENERGY AND MOLECULAR BUILDING BLOCKS

TO GROW, TO REPRODUCE AND TO MAINTAIN DYNAMIC HOMEOSTASIS.

ESSENTIAL KNOWLEDGE 2.B.3: EUKARYOTIC CELLS MAINTAIN INTERNAL MEMBRANES THAT PARTITION THE CELL INTO SPECIALIZED REGIONS.

• Learning Objectives:• (2.13) The student is able to explain how internal

membranes and organelles contribute to cell functions.• (2.14) The student is able to use representations and

models to describe differences in prokaryotic and eukaryotic cells.

OVERVIEW: THE FUNDAMENTAL UNITS OF LIFE

• All organisms are made of cells• The cell is the simplest collection of matter

that can live• Cell structure is correlated to cellular function• All cells are related by their descent from earlier cells

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

TYPES OF CELLS

• The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic

• Eukaryotic cells have internal membranes that compartmentalize their functions• Protists, fungi, animals, and plants all consist of eukaryotic cells

• Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells


COMPARING PROKARYOTIC AND EUKARYOTIC CELLS

• Basic features of all cells: • Plasma membrane• Semifluid substance called cytosol• Chromosomes (carry genes)• Ribosomes (make proteins)


PROKARYOTES VS. EUKARYOTES

• Prokaryotes:• NO NUCLEUS, but do have nucleoid region with DNA present • Small and Simple – few organelles • Have cell membranes and cytoplasm

• Ex. Bacteria and Archaea

• Eukaryotes:• Contain nuclei • Contains organelles that perform specialized functions • Unicellular or multicellular

• Ex. Plants, animals, protists, fungi

Fig. 6-6

Fimbriae

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella

Bacterialchromosome

(a) A typical rod-shaped bacterium

(b) A thin section through the bacterium Bacillus coagulans (TEM)

0.5 µm

EUKARYOTIC CELLS

• Eukaryotic cells are characterized by having• DNA in a nucleus that is bounded by a membranous nuclear

envelope• Membrane-bound organelles• Cytoplasm in the region between the plasma membrane and

nucleus

• Eukaryotic cells are generally much larger than prokaryotic cells


A VIEW OF THE EUKARYOTIC CELL

• A eukaryotic cell has internal membranes that partition the cell into organelles

• Plant and animal cells have most of the same organelles-• Not in Animal Cells:

• Chloroplasts | central vacuole | tonoplast | cell wall | plasmodesmata

• Not in Plant Cells:• Lysosomes | centrioles | flagella


Fig. 6-9a

ENDOPLASMIC RETICULUM (ER)

Smooth ERRough ERFlagellum

Centrosome

CYTOSKELETON:

Microfilaments

Intermediatefilaments

Microtubules

Microvilli

Peroxisome

MitochondrionLysosome

Golgiapparatus

Ribosomes

Plasma membrane

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

Fig. 6-9b

NUCLEUS

Nuclear envelopeNucleolus

Chromatin

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Ribosomes

Central vacuole

Microfilaments

Intermediate filaments

Microtubules

CYTO-SKELETON

Chloroplast

PlasmodesmataWall of adjacent cell

Cell wall

Plasma membrane

Peroxisome

Mitochondrion

Golgiapparatus

ORGANELLES: EMERGENT PROPERTIES

• All biological systems are composed of parts that interact with each other. These interactions result in characteristics not found in the individual parts alone. In other words, “THE WHOLE IS GREATER THAN THE SUM OF ITS PARTS.” • This phenomenon is referred to as emergent properties.

• All biological systems from the molecular level to the ecosystem level exhibit properties of biocomplexity and diversity.

• Together, these two properties provide robustness to biological systems, enabling greater resiliency and flexibility to tolerate and respond to changes in the environment.


INTERNAL MEMBRANES FACILITATE CELLULAR PROCESSES.

• Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface area where reactions can occur.

• Membranes and membrane-bound organelles in eukaryotic cells localize (compartmentalize) intracellular metabolic processes and specific enzymatic reactions.

• Archaea and Bacteria generally LACK internal membranes and organelles and have a cell wall.

COMPARTMENTALIZATION IN CELLS

• Subcellular Structures that Function in Control:• Nucleus (plant and animal)• Centrosome (plant and animal)

• Subcellular Structures that Function in Assembly, Transport, and Storage:• Endoplasmic reticulum (plant and animal)• Ribosomes (plant and animal)• Golgi apparatus (plant and animal)• Vacuoles (plant -1 large, and animal - many)• Lysosomes (animal)• Leucoplasts (plant only)

• Subcellular Structures that Function in Energy Transformations:• Chloroplasts and Chromoplasts (plant only)• Mitochondria (plant and animal)


Fig. 6-10 – The Nucleus

NucleolusNucleus

Rough ER

Nuclear lamina (TEM)

Close-up of nuclear envelope

1 µm

1 µm

0.25 µm

Ribosome

Pore complex

Nuclear pore

Outer membraneInner membraneNuclear envelope:

Chromatin

Surface ofnuclear envelope

Pore complexes (TEM)

THE ENDOMEMBRANE SYSTEM

• The endomembrane system regulates protein traffic and performs metabolic functions in the cell

• Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface area where reactions can occur.

• Components of the endomembrane system:• Nuclear envelope• Endoplasmic reticulum• Golgi apparatus• Lysosomes• Vacuoles• Plasma membrane

• These components are either continuous or connected via transfer by vesicles


FIGURE 7.16: RELATIONSHIPS AMONG ORGANELLES OF THE ENDOMEMBRANE SYSTEM

LYSOSOMES: DIGESTIVE COMPARTMENTS

• A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules

• Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids

• Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole

• A lysosome fuses with the food vacuole and digests the molecules

• Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy


FIGURE 7.14 THE FORMATION AND FUNCTIONS OF LYSOSOMES (LAYER 1)

Fig. 6-14

Nucleus 1 µm

Lysosome

Digestiveenzymes

Lysosome

Plasmamembrane

Food vacuole

(a) Phagocytosis

Digestion

(b) Autophagy

Peroxisome

Vesicle

Lysosome

Mitochondrion

Peroxisomefragment

Mitochondrionfragment

Vesicle containingtwo damaged organelles

1 µm

Digestion

In phagocytosis, large substances are taken up by a cell and digested by lysosome enzymes.

In autophagy, lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules.

APOPTOSIS – PROGRAMMED CELL DEATH

• Programmed destruction of cells (apoptosis) by their own lysosomal enzymes is important in the development of many multicellular organisms (such as tadpoles into frogs).

• This even occurs in the hands of human embryos (which are webbed until lysosomes digest the tissue between the fingers).


LYSOSOMAL DISORDERS

• A variety of inherited disorders called lysosomal storage diseases affect lysosomal metabolism. • In Pompe’s disease, the liver is damaged by an accumulation of

glycogen due to the absence of a lysosomal enzyme needed to break down that polysaccharide.

• In Tay-sacs disease, a lipid-digesting enzyme is missing or inactive, and the brain becomes impaired by an accumulation of lipids in the cells.


The Golgi Complex

cis face(“receiving” side of Golgi apparatus) Cisternae

trans face(“shipping” side of Golgi apparatus)

TEM of Golgi apparatus

0.1 µm

Fig. 6-11: Ribosomes

Cytosol

Endoplasmic reticulum (ER)

Free ribosomes

Bound ribosomes

Large subunit

Small subunit

Diagram of a ribosomeTEM showing ER and ribosomes

0.5 µm

Fig. 6-12Smooth ER

Rough ER Nuclear envelope

Transitional ER

Rough ERSmooth ERTransport vesicle

RibosomesCisternaeER lumen

200 nm

FUNCTIONS OF SMOOTH ER

• The smooth ER• Synthesizes lipids• Metabolizes carbohydrates• Detoxifies poison• Stores calcium


FUNCTIONS OF ROUGH ER

• The rough ER• Functions to compartmentalize the cell, serves as

mechanical support, provides site-specific protein synthesis with membrane-bound ribosomes.

• Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates)

• Distributes transport vesicles, proteins surrounded by membranes

• Is a membrane factory for the cell


PATHWAY OF PROTEIN-BASED SECRETION


MITOCHONDRIA & CHLOROPLASTS

• Mitochondria and chloroplasts change energy from one form to another

• Mitochondria are the sites of cellular respiration, a metabolic process that generates ATP

• Chloroplasts, found in plants and algae, are the sites of photosynthesis


MITOCHONDRIA AND CHLOROPLASTS

• Mitochondria and chloroplasts • Are not part of the endomembrane system• Have a double membrane• Have proteins made by free ribosomes• Contain their own DNA


Fig. 6-17

Free ribosomesin the mitochondrial matrix

Intermembrane space

Outer membrane

Inner membraneCristae

Matrix

0.1 µm

Fig. 6-18

Ribosomes

Thylakoid

Stroma

Granum

Inner and outer membranes

1 µm

A Living Unit is Greater than the Individual Sum of Its Parts

5 µ

m

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