Lecture 5: Cellular Biology II

I. Nucleus: control center for cellular function; contains genetic material

A. Number of nuclei

1. Most cells have a single nucleus

2. Large cells (those with a large amount of cytoplasm) have to be multinucleate

3. Red blood cells—only cell lacking a nucleus

B. Structures

1. Nuclear envelope

            a. Double membrane—inner and outer

                        i. Outermembrane is continuous with ER

                        ii. Nuclear pores

                        iii. Selectively permeable

            b. Perinuclear cisterna—fluid between membranes

2. Nucleoli

            a. No membrane

            b. Ribosomes subunits are assembled here

                        i. Large in growing cells

            c. Associated with chromatin region associated with DNA coding for rRNA

                        i. Nuclear organizing regions (DNA regions)

3. Chromatin—DNA + globular histone

            a. Nucleosome—fundamental unit of chromatin

                        i. Units of eight wrapped by DNA molecule

b. Chromosomes: prior to cell division, chromatin condenses to form chromosomes

 

II. Cell Life Cycle

The cell cycle includes all events from a cell’s formation until it divides. The cell cycle includes two major periods: interphase and cell division (mitosis).

A. Interphase: from cell formation until cell division

1. Metabolic or growth phase: all non-replication activities

2. Preparation for division

3. Subphases:

            a. G1: growth phase with little cell division related activites

                        i. Can last minutes to years (G0)

            b. S: synthetic phase; DNA replicates

c. G2: brief period of growth where enzymes and other proteins necessary for division are synthesized

            i. Very brief

4. DNA replication (Do not need to know molecular events)

B. Cell Division

1. Mitosis and cytokinesis

2. Characteristics of mitosis

            a. Daughter cells (2) are identical to mother cell

            b. No gain or loss of genetic material

            c. Series of continuous events

            d. Lasts about two hours

3. Phases of mitosis

            a. Prophase

                        i. Prior to the start of prophase, centrioles have replicated (two pairs)

                        ii. Chromatin condenses to form chromosomes

                        iii. Chromosomes already replicated and consist of two sister chromatids

                        iv. Sister chromatids are connected by centromere

                        v. Nuceoli disappear

vi. Centriole pairs are rearranged to focal loci for mitotic spindles (microtubules)

vii. Nuclear membrane disappears and spindles interact with chromosomes

viii. Spindles attach to kinetochores (proteins on centromere)

ix. Kinetochore microtubules pull chromatids to center of the cell

            b. Metaphase

                        i. Chromosomes cluster at the middle of the cell

                        ii. Metaphase plate

            c. Anaphase

                        i. Centromeres of the chromosomes split

                        ii. Each chromatid is now a chromosome

                        iii. Kinetochore fibers contract and pull chromosomes towards poles

                        iii. Poles of cells are pushed apart to elongate the cell

                        iv. V-shaped

                        v. Shortest stage; minutes

            d. Telophase

                        i. Chromosome movement stops

                        ii. Chromosomes uncoil to form chromatin

                        iii. Nuclear membrane reforms

                        iv. Nucleoli reform

                        v. Spindles disassemble

4. Cytokinesis—peripheral microfilaments contract at the cleavage furrow to squeeze the cells apart

 

C. Meiosis (Chapter 28): gamete production; two consecutive divisions produce four daughter cells each with half as many chromosomes as mother cell

1. Nuclear divisions: Meiosis I and meiosis II

2. Meiosis I (preceded by interphase where DNA is replicated): Reduction Division

            a. Prophase I

                        i. Chromosome form, nuclear membrane and nucleolus disappear

ii. Synapsis: homologous chromosomes form tetrads; crossover points form (chiasmata)

            b. Metaphase I

                        i. Tetrads align on equatorial plate

            c. Anaphase I

                        i. Centromeres do not break (sister chromotids remain paired)

ii. Homologous chromosomes separate, breaking at crossover points (exchange parts of chromosomes)

iii. Paternal and maternal chromosomes are separated

            d. Telophase I

                        i. Same events as telophase of mitosis

                        ii. Cytokinesis follows

iii. Daughter cells are haploid (Diploid amount of DNA but haploid chromosomal number)

3. Meiosis II (Like mitosis without DNA replication during interphase)

a. Four daughter cells are produced each genetically unique from original mother cells

 

III. Cancer

Terms:

A. Neoplasia—increase in new cells

1. Dystrophy—disorder arising from abnormal change in cell size

            a. Hypertrophy—increase in size of cells

2. Dyplasia—disorder arising from abnormal change in cell number

            a. Hyperplasia—increase in number of cells

            b. Aplasia—decrease in cell number

                        i. Normal during development

                        ii. Occurs later in life (e.g., dementias, osteoporosis)

B. Tumor—unchecked growth of genetically abnormal cells

1. Classification based on characteristics

            a. Benign

                        i. Looks like normal tissue

                        ii. Grows slowly

                        iii. Does not invade

            b. Malignant: Cancer

                        i. Poorly differentiated

                        ii. Grow fast

                        iii. Invasive

                        iv. Metastasize

2. Classification based on origin

            a. Carcinomas—epithelial origin

                        i. Glandular

                        ii. Squamous

                        iii. Melanocyte

            b. Sarcomas—connective tissue origin

                        i. Cartilage

                        ii. Bone

                        iii. Fibrous connective

                        iv. Meninges

3. Classification based on prognosis or therapy

            a. Tumor mass

            b. Lymph involvement

            c. Metastasis

 

C. Epidemiology—cause of disease; factors that lead to cancer

For a few rare situations, there are known genetic defects (e.g., retinoblastoma) or viral agents (e.g., Burkitt’s lymphoma). But for most other cancers, the specific cause is not known.

A. Risk factors

1. Host factors

            a. Age

            b. Sex

            c. Psychological factors

            d. Genetic factors

2. Environmental and lifestyle factors

            a. Geographic location

            b. Nutrition

            c. Occupation

                        i. Asbestos

                        ii. Pesticides

                        iii. Radiation

            d. Cigarette smoking

 

D. Etiology

1. Cancer has no single cause. Its etiology is complex, requiring both:

            a. DNA damage

            b. Inadequate physiological defense or repair

2. Initiation of cancer—Neoplastic Transformation

            a. Arise from a single cell

            b. Cell suffers multiple transforming genetic mutations

                        i. Mutations are either inherited or acquired

3. Acquired mutations

            a. Random events during DNA replication

            b. Induced by mutagens (carcinogens)

4. Initial DNA damage promotes accumulation of further damage

            a. Damage typically involves genes that normally:

                        i. Induce cell proliferation or growth (proto-oncogenes)

                        ii. Inhibit growth of damaged cells (tumor suppressor genes)

 

E. Treatment

1. Surgery—resection of the tumor

2. Radiation therapy—x-rays or gamma rays delivered to the tumor; induce apoptosis in radiosensitive cells (including normal cells)

3. Chemotherapy (antineoplastic agents)—cytotoxic drugs that induce DNA damage; normal cells are often better at repair and less vulnerable to apoptosis

4. Bone marrow transplantation—certain cancers require high doses of radiation or chemotherapy; such treatment is toxic to bone marrow

5. Biological response modifiers—agents that boost immune system response or antagonize tumor growth through other biological effects (e.g., interferon, cytokines, etc.)

6. Gene therapy—modify gene function; include synthetic nucleotide strands to repair DNA, antisense strands to prevent gene expression, insertion of gene sequences to produce normal gene products

 

End Cell Biology

 

Tissue I

Tissue—a group of closely associated cells performing a restricted range of functions.

 

Overview of Tissues

 

 

Tissue Type

Nervous

Muscle

Epithelial

Connective

Primary Function

Information Processing

Contraction to Generate Force

Cover Exposed Surfaces

Structure and Support

Cell Types

Neurons

Glia

Smooth

Cardiac

Skeletal

Squamous

Cuboidal

Columnar

Transitional

Glandular

Fibroblasts

WBC’s

Mast Cells

Plasma Cells

Macrophages

Adipocytes

Fibers

(Minimal)

(Minimal)

Basement Membrane

Collagen

Reticular

Elastic

Fluids

Nutrient-Rich, Aqueous

(Minimal)

(Limited)

Depends on Type of Connective Tissue

 

I. Classes of Tissue

A. Nervous Tissue

1. Neurons

            a. Chemical and electrical transmission of information

2. Glia

            a. Support and repair

 

B. Muscle

1. Function: Contracts to generate force

2. Types

            a. Skeletal

                        i. Striated

                        ii. Multinucleated

                        iii. Voluntary control

            b. Smooth

                        i. Non-striated

                        ii. Uninucleated

                        iii. No voluntary control

            c. Cardiac

                        i. Striated

                        ii. Intercalated disks

                        iii. No voluntary control

 

C. Epithelial

1. Functions:

            a. Protection

            b. Absorption

            c. Filtration

            d. Secretion

2. Characteristics

            a. Cellularity: close-packed cells with limited extracellular material

            b. Cellular connections

                        i. Tight junctions

                        ii. Desmosomes

            c. Cellular organization

                        i. Apical surface in contact with fluid or air

                        ii. Basal cell layer in contact with basement membrane (lamina)

            d. Connective tissue support

                        i. All epithelial sheets are supported by connective tissue

ii. Deep to the basement lamina is a layer of connective tissue—reticular lamina

iii. Basement lamina + reticular lamina = basement membrane

            e. Innervated—receives nervous innervation

            f. Avascular—contains no blood vessels

            g. Highly regenerative

                        i. Cells are replaced rapidly by cell division

                        ii. Cell loss due to friction and contact with hostile environments


3. Classification

 

4. Nomenclature

            a. Two names

                        i. First indicates number of cell layers

                        ii. Second indicates cell shape

            b. All cells in a given layer will have the same shape

5. Epithelial layers

            a. Simple

                        i. Single cell layer

                        ii. Areas of absorption and filtration

            b. Stratified

                        i. Two or more cell layers

                        ii. Areas of high abrasion

6. Cell shape: all cells have six irregular sides that differ in height

            a. Squamous

                        i. Flattened

                        ii. Scale-like

            b. Cuboidal

                        i. Boxlike

                        ii. As tall as wide

            c. Columnar

                        i. Tall

7. Shape of nucleus

            a. Conforms to cell shape

                        i. Squamous—disc shaped

                        ii. Cuboidal—spherical

                        iii. Columnar—elongated from top to bottom

8. Types of Simple Epithelia

            a. Simple squamous

            b. Simple cuboidal

            c. Simple columnar

            d. Pseudostratified columnar

9. Types of Stratified Epithelia

            a. Stratified squamous

                        i. Cell shape varies according to layer

                        ii. Name is based on shape of apical surface

            b. Stratified cuboidal

            c. Simple columnar

            d. Transitional epithelia

 

Nonglandular Epithelia

I. Simple

A. Simple squamous

1. Function

            a. Diffusion and filtration

2. Location

            a. Endothelium

                        i. Lining of lymphatic system

                        ii. Lining of all organs in cardiovascular system

            b. Mesothelium

                        i. Serous membrane linings of ventral body cavity

B. Simple cuboidal

1. Function

            a. Secretion and absorption

C. Simple columnar

1. Function

            a. Absorption and secretion

2. Location

            a. Digestive tract

3. Modifications

            a. Dense microvilli on apical surface

            b. Goblet cells that secrete protective lubricant

D. Pseudostratified columnar

1. Single layer of cells that vary in height

2. Only tallest reach apical surface

3. Nuclei are located at different heights

4. Function

a. Absorption and secretion

5. Modifications

            a. Ciliated with mucous cells

                        i. Mucous traps particulate matter

                        ii. Cilia propel trapped matter out

 

II. Stratified epithelia

A. Characteristics

1. Two or more cell layers

2. Regenerate from below via mitotic division

            a. Basal cell divide

            b. Move apically to replace older surface cells

3. Durable

4. Protection

B. Stratified squamous

1. Surface cells are squamous

2. Deep layers consist most often of cuboidal

3. Location

            a. Areas of abrasion

            b. Forms external surface of the body

                        i. Extends into all body openings

                        ii. Outer layer (epidermis) is keratinized

4. Surface cells are flattened and atrophied

C. Stratified cuboidal and columnar are rare

D. Transitional

1. Location

            a. Lining of urinary organs

                        i. Need to stretch (undergo a transition)

2. Cell organization

            a. Basal surface—cuboidal or columnar

            b. Apical surface

                        i. Unstretched—rounded and dome-like

                        ii. Stretched—flattened; squamous-like

            c. Cell layers

                        i. Unstretched—six layers

                        ii. Stretched—three layers

 

Glandular Epithelia 

A. Terms:

1. Gland: consist of one or more cells that make and secrete a particular product

2. Secretion: refers to both  the aqueous product of glandular cells and the process of making that product

a. Formation involves active processes

i. Made in ER, packaged in Golgi (secretory vesicles), secreted by exocytosis

B. Classification

1. Route of secretion

a. Exocrine

            i. Secrete via ducts

            Secrete onto body surface or cavities

b. Endocrine (Discussed later)

i. Ductless

            ii. Secrete directly into extracellular space

2. Cell number

            a. Unicellular

            b. Multicellular

C. Multicellular exocrine glands

1. Common elements

            a. Duct derived from epithelium

            b. Secretory unit consisting of secretory cells

            c. Supportive connective tissue

                        i. Supplies blood and nervous fibers

            d. Fibrous capsule

                        i. May penetrate gland and divide it into lobes

2. Classification based on duct structures

            a. Simple

                        i. Single unbranched duct

            b. Compound

                        i. Branched duct

3. Classification based on secretory parts

            a. Tubular

                        i. Secretory cells form a tube

            b. Alveolar

                        i. Secretory cells form a flask-like sac

            c. Tubuloalveolar

                        i. Contain both

4. Classification based on how product is secreted

            a. Merocrine glands

                        i. Secrete via exocytosis without altering secretory cell

            b. Holocrine glands

i. Accumulate products until cell bursts, releasing secretory products, then dies

            c. Apocine glands

                        i. Accumulate products just beneath free surface

                        ii. Top of cell is removed and products are released

                        iii. Cell is repaired

D. Unicellular exocrine glands

1. Single cells scattered in epithelial sheet

2. Ductless

3. Goblet cells

            a. Produce mucin

            b. Protects and lubricates surfaces