Chapter 7Cell Structures

Viruses- Considered nonliving in biologya. protein coat- capsidb. DNA/ RNA core

Prokaryotes vs EukaryotesProkaryotes EukaryotesNo nucleus- DNA in nucleiod area(DNA- circular/ no histone proteins)

Nucleus- DNA stored here(DNA- linear/ along w/ histone proteins)

Lacks membrane bound organelles Contains specialized organellesUnicellular MulticellularSmaller/ simpler Larger/ complex1-10 microns in diameter 10-100 microns in diameterDomain Bacteria & Archaea Domain Eukarya Kingdoms:

Protista, Fungi, Plantae, Animalia

*** Common features:- Cell membrane, cytoplasm, chromosomes, ribosomes

Contributions to Cytology:a. Robert Hooke (1665)- 1st to observe cells viewing

a slice of cork/ coined to the term “cells”b. Anton van Leeuwenhoek- 1st to view living cells

(protists- “animalcules”)c. M.J. Schleiden (1838)- plants composed of cellsd. Theodor Schwann (1839)- animals composed of

cellse. Robert Virchow (1858)- cells come from pre-

existing cells

Cell Theory

• Schleiden, Schwann, and Virchow contributed to the cell theory

1. All living things are composed of cells2. Cells are the basic unit of structure and

function3. Cells produced from pre-existing cells

Eukaryotic Cell Structures

• Domain Protista, Fungi, Plantae, and Animalia• Organelle “Little organ”

– Specialized subunits within a cell that has a specific function

– Usually enclosed within its own membrane

*** NOTE: [*] =These structures contain DNA and are capable of replication

a. Cell Membrane (Plasma membrane)

• Double layer of protein and lipid around ALL cells

• Separates the interior of a cell from the outside environment

• Semi-permeable (selective) allows only certain substances to pass through

Cell Membrane- Lipid Bilayer

b. Cell Wall

• Rigid, nonliving structure outside the cell membrane

• Not present in Animals, but present in: 1. Plants & some protists (algae) cellulose- provides support to cells2. Fungi chitin

c. Nucleus

• Double membrane bound organelle• Contains genetic material DNA• Known as the “control center of the cell”

d. [*] Chromosome

• Found within nucleus• Single DNA molecule• Segments represent

different genes • Within eukaryotic cells:

composed of DNA and proteins chromatin

• Principal nuclear structure visible during cell division

e. Nucleolus (i)• Small dense organelle within nucleus• Contains DNA, RNA, & protein• Within eukaryotic cells:assemble ribosomes

• Lily parenchyma cell (TEM x7,210) Note the large nucleus and nucleolus in the center of the cell

f. Nuclear Membrane (Envelope)

• Double membrane that surrounds the nucleus• Semi-permeable (selective)• Consists of protein-lipid molecules

g. Cytoplasm (Cytosol)

• All living material between the nuclear and plasma membrane

• Semi-liquid substance that contains organellesEx: ribosomes, chloroplasts, mitochondria

h. Ribosomes• Small organelles composed of

ribosomal RNA (rRNA) and proteins• 2 types:

1) Attached - Found on rough endoplasmic reticulum (RER) - Synthesizes extracellular proteins

2) Free - Found in cytoplasm - Synthesizes intracellular proteins

***[NOTE: Protein functions= a. enzymes/ b. structural parts]

i. [*] Mitochondrion (ia)• Double membrane bound

organelle• Produces ATP energy for ALL

cells• Contains own DNA and

ribosomes• Site of cellular respiration (Krebs

Cycle, respiratory chain, and oxidative phosphorylation)

j. Endoplasmic Reticulum (ER)

• Extensive system of membrane present in most eukaryotic cells

• Material transported through these channels and canals

• May connect to nuclear or cell membranes

Cont. Endoplasmic Reticulum• 2 types:

1)Rough ER (RER) - Ribosomes attached to RER/gives “rough” appearance - Synthesizes proteins and other materials for export

2) Smooth ER (SER) - No ribosomes attached

- Synthesizes lipids and steroids - Metobolizes CHOs - Detoxify drugs and poisons

k. Golgi Apparatus

• Layer of flattened, disc-shaped sacs, tubules, and vesicles near nucleus of gland cells

• Synthesizes cell secretions

• Source of lysosomes

l. Vacuoles

• Membrane-bound sac• Transport raw materials

to cell interior• Also transport wastes• Used for storage of

water/ food• In plant cells: typically

large and central

Vacuole in Plant Cell

m. Lysosomes• Double membrane bound sac

containing hydrolytic enzymes- Hydrolytic (“water-splitting”) breakdown substances by adding H2O

• Fuse with food vacuoles to digest contents

• “Suicide bag” digest cytoplasm if membrane ruptures

• - Present in white blood cells (WBC): leukocytes

n. [*] Plastids• Cytoplasmic, often pigmented

organelle in plant cells

• Includes:1. Amyloplast - Stores starch - Root and internal stem tissue- not exposed to light

2. Chromoplast - Contain variety of carotenoids yellow, red, orange pigments/ - Ex: carrots, tomatoes

Parenchyma cell containing chromoplasts: each red dot is a chromoplast that contains carotenoids

Amyloplasts in a potato cell

Cont. Plastids3. Chloroplast

- Contain carotenoids and chlorophylls a, b, c, d, e

- Contains DNA and ribosomes- Site for photosynthesis

o. Cytoskeleton

• Network of protein scaffolding or “skeleton” of the cytoplasm

• Provides shape, organization, and movement

• Consists of: 1. Microfilaments

- Thinnest, solid protein

tubules - Hold organelles in place - Enable cells to change

shape 2. Intermediate Filaments

Cont. Cytoskeleton3. Microtubules - Thickest, hollow protein rods

- Provides shape and support to cells- Serve as “tracks” for organelles to move on- Makes up the following:

a. [*] Centrioles • Forms spindle pole during mitotic and meiotic

cell division• Found in pairs at right angles near nucleus of

animal cells• Have own DNA• Microtubules in triplets• Present ONLY in animal cells

Cont. Microtubulesb. Cilium (ia)

• Short, numerous structures embedded in the surface of some eukaryotic cells

• Arranged in rows (9 + 2 arrangement of microtubules)

• Involved in locomotion and movement of substances across surface

c. Flagellum (a)• Long, single threadlike organelle • Used in locomotion• 9 +2 arrangement of microtubules

p. Kinetosome• Motion-controlling granules at

base of flagella and cilia q. Fibrils• Protein molecules that form

spindles during plant and cell division

• Functions in specialized cells: a. muscle contractionb. nerve cells carry impulses

r. Pinocytic Vesicle• Indentation in cell membrane

which results in vacuole formation

• 2 types:1) Pinocytosis -“Cell drinking” - Intake of fluid by cell2) Phagocytosis - “Cell eating” - Intake of solids - Function of WBC

(leukocytes)

s. Contractile Vacuole• Expels excess water in freshwater organisms

placed in hypotonic environment/ ex: distilled water

• Maintains appropriate concentrations of salts and other molecules

EUKARYOTIC CELLS PROKARYOTIC CELLS

Nucleus present? Yes, organized No, lack nuclear membrane

Membrane-enclosed organelles present?

Yes No

Chromosomes present? Yes, in pairs Yes, single

Cytoplasmic streaming present? Yes No

Cell division by mitosis? Yes No

Type of flagella present? Complex Simple

Type of ribosomes present? Large Small

Type of cytoskeleton present? Complex Simple

Cellulose present in cell wall? Yes No

DNA bound to histone proteins? Yes No

Prokaryotic Cell Structures

- Domain Archeabacteria and Eubacteria

a. Plasmid small circular DNA separated from main chromosomeb. Mesosome infolding of plasma membrane significant in copying DNA prior to divisionc. Nucleiod area of cell containing the main chromosome

Prokaryotic Replication