Cytology

Number of distinguishable cell types

Over 200 distinguishable cell types in the body

4 Basic tissues

Epithelia, connective tissue, muscle, and nerve

Epithelia location

Cover body exterior surfaces and line body cavities, including blood vessels

Epithelia and glands

Epithelia form both exocrine and endocrine glands

Epithelial cell adherence

Cells are tightly adherent to one another

Epithelial cell shapes

Can be squamous, cuboidal, or columnar

Epithelia functions

Includes protection, absorption, secretion, excretion, and gas exchange

Connective tissue cell density

Consists of relatively few cells that are not adherent to each other

Connective tissue vascularity

Vascular (unlike epithelium)

Connective tissue matrix

Contains an abundant matrix

Connective tissue function: structural

Cohesion of structural elements

Connective tissue function: distribution

Medium through which blood vessels distribute nutrients and take up metabolic waste

Connective tissue function: defense

Involved in immune and inflammatory responses

Connective tissue function: repair

Involved in tissue repair following injury

Muscle tissue function

Responsible for movement and changes in size and shape of body organs

Muscle cell orientation

Elongated cells usually oriented parallel to each other and organized in bundles

Sarcoplasm

The name for muscle cell cytoplasm

Main sarcoplasm components

Occupied mostly by the myofilaments actin and myosin

Muscle filament arrangement

Highly organized to allow for contraction

Nervous system responsibility

Responding to the environment and maintaining coordinated functional activities of organs and organ systems

2 Main nerve cell types

The neuron and supporting cells

4 Common features of cells

Surrounded by a membrane, zero to many nuclei, contain organelles, and contain inclusions

Nucleus definition

Membrane-limited organelle that contains the genetic information of the cell

Nucleus function: DNA replication

Site of replication of DNA as required for cell division

Nucleus function: repair

Site of DNA repair

Nucleus function: transcription

Site of RNA transcription and processing

3 Major components of the nucleus

Nuclear envelope, chromatin, and nucleolus

4 Components of the nuclear envelope

Outer nuclear membrane, inner nuclear membrane, nuclear pores, and nuclear lamina

Importance of nuclear morphology

Important in determining the health of a cell, as in tumor cell development

Normal nucleus shapes

Round, ellipsoid, infolded, or lobulated

Normal nucleus number

Varies from none to multi

Normal nucleus location

Central, basal, or eccentric

Nuclear envelope structure

Consists of two unit membranes separated by a 10-30 nm space

Outer nuclear membrane face

Faces the cytoplasm

Outer nuclear membrane continuity

Continuous with and shares properties with the rER

Outer nuclear membrane attachments

Can have ribosomes attached to the cytoplasmic surface

Inner nuclear membrane face

Faces the nuclear matrix

Inner nuclear membrane support

Supported by the nuclear lamina

Inner nuclear membrane associations

Associates with chromatin

Perinuclear cisternae

The space between the two unit membranes of the nuclear envelope

Membrane continuity point

The inner and outer nuclear membranes are continuous with one another at the nuclear pores

Nuclear pore function

Bidirectional “gates” for trafficking of molecules between the nucleus and the cytoplasm

Diffusion through nuclear pores

Small molecules less than 40–60 kd pass through by diffusion

Energy-dependent nuclear transport

Required for proteins of any size containing a nuclear localization sequence

Nuclear transport energy sources

Requires either ATP or GTP

Nucleoporins

The specific proteins that constitute the nuclear pore

Nuclear pore structure

Contains a central cylindrical body between inner and outer octagonal rings

Nuclear pore ring components

Each ring contains 8 protein particles

Nuclear basket

Formed by protein filaments extending from the rings on the nuclear side

Nuclear lamina location

Located between the inner nuclear membrane and the peripheral heterochromatin

Nuclear lamina composition

Made up of intermediate filament proteins called lamins (A, B, and C)

Nuclear lamina function: envelope stability

Gives shape and stability to the nuclear envelope

Nuclear lamina function: organization

Organizes the interphase nucleus

Nuclear lamina function: structural link

Acts as a structural link between chromatin and the nuclear envelope

Nuclear lamina function: cell division

Responsible for the dissolution and reformation of the nuclear envelope during division

Nuclear lamina function: pore position

Positions nuclear pore complexes within the nuclear envelope

Dissolution of nuclear lamina

Caused by lamin phosphorylation at mitosis

Laminopathies/Envelopathies

Inheritable diseases resulting from mutations in nuclear membrane, pores, or lamins

Laminopathy disease examples

Striated muscle disorders, partial lipodystrophy, peripheral neuropathies, progeroid syndromes

Chromatin

Complex of DNA, histone, and non-histone proteins found in eukaryotic nuclei

Chromosome

Structure of a very long DNA molecule and associated proteins

Chromosome visibility

Readily visible during meiosis or mitosis when they become condensed

Chromatid

One copy of a chromosome formed by DNA replication, joined at the centromere

Heterochromatin appearance

Electron-dense portions of the nucleus

Heterochromatin transcription status

Represents genes that are not being transcribed

Constitutive vs Facultative heterochromatin

Constitutive is never transcribed

Euchromatin (Extended chromatin)

Uncoiled or loosely packed portions of chromosomes

Euchromatin transcription status

Represents genes that are being transcribed

Barr body

The inactive, highly coiled X chromosome in females

Barr body appearance

Small drumstick or clump of heterochromatin adjacent to the nuclear envelope

Nucleolus Nucleolus location

Usually eccentrically placed in the interphase nucleus

Nucleolus membrane status

Not surrounded by a membrane

Nucleolus number

1-2 per cell depending on species and synthetic activity

Nucleolus major function

Site of ribosomal RNA (rRNA) transcription and synthesis

Nucleostemin

Protein in the nucleolus that regulates the cell cycle

Nucleolus composition

Rich in rRNA and protein

3 Areas of the nucleolus

Fibrillar center (pale), pars fibrosa (dense), and pars granulosa (granular)

Nucleolar Organizing Regions (NORs)

Regions on ten interphase chromosomes containing genes that encode rRNA

NOR function

Help reorganize the nucleoli following cell division

RNA and Ribosomes RNA composition

Linear molecule with ribose sugar and uracil instead of thymine

RNA synthesis

Synthesized by the transcription of DNA

messenger RNA (mRNA) function

Contains sequences that code for amino acids

transfer RNA (tRNA) function

Transfers the correct amino acid to the ribosome

ribosomal RNA (rRNA) function

Forms ribosomes in association with specific proteins

Ribosome definition

The sites of protein synthesis

Large ribosomal subunit components

5S, 28S, and 5.8S rRNA plus ~49 proteins

Large ribosomal subunit function

Catalyzes peptide bond formation

Small ribosomal subunit components

18S rRNA and ~33 proteins

Small ribosomal subunit function

Binds mRNA and tRNA

Svedberg units (S)

Measure of sedimentation used to describe macromolecule size

Ribosome appearance in EM

Appear as granular material in the cytoplasm

Ribosome cytoplasmic associations

Outer nuclear membrane and endoplasmic reticulum

Polyribosomes

Clusters of ribosomes around a single strand of mRNA

Events in nucleolus (Ribosome formation)

Transcription of rDNA to pre-rRNA, association with proteins, and cleavage

Ribosome formation in nucleus

28S and 5.8S combine with 5S rRNA to form large subunit

Ribosome formation in cytoplasm

Assembly of subunits into ribosomes and polysomes in the presence of mRNA

II. Membranes 4 Membrane concepts

Not homogenous, in constant flux, asymmetric, shape determined by cytoskeleton

Unit membrane structure

Trilaminar structure of two electron dense lines (leaflets) separated by an electron lucent zone

Membrane mass composition

Lipids make up 50% of membrane mass

Lipid function in membranes

Responsible for membrane form and permeability properties