Chapter 4: Cytology

Ribosomes

Cytoplasmic organelles where proteins are synthesized

Plasma membrane

Composed of phospholipids, cholesterol, and proteins that encloses the cell contents

Separates the body’s two main fluid components:

• Intracellular space (inside the cell)

• Extracellular space (outside the cell)

Plasma membrane - Cholesterol

A steroid that stabilizes the membrane’s structure in the face of changing temperatures

Plasma membrane - Integral proteins

Span the width of the membrane

Plasma membrane - Peripheral proteins

Located on only one face of the membrane

Plasma membrane - Glycoproteins and glycolipids

Cell recognition

Microvilli

Tiny projections on the free surface of some epithelial cells, increases surface area for absorption

In parts of the body where rapid absorption is necessary the plasma membrane is folded into…

Projections called microvilli

Which type or organelle contains its own DNA and ribosomes?

Mitochondria

Golgi Apparatus

Membrane-enclosed sacs system close to the cell nucleus that packages protein secretions for export, packages enzymes into lysosomes for cellular use, and modifies proteins destined to become part of the cellular membrane

Ribosomes

Cytoplasmic organelles composed of proteins and RNA (ribosomal RNA) where proteins are synthesized

• Not enclosed by a membrane

Peroxisome

Membranous sacs in the cytoplasm containing powerful oxidase enzymes that use molecular oxygen to detoxify harmful or toxic substances such as red radicals

Also synthesize phospholipids that are critical for normal functioning of the nervous system

Cytosol

Viscous, semitransparent fluid substance of cytoplasm in which other element are suspended

Contains water, solutes, RNA, enzymes, and other proteins

Mitochondria

Responsible for ATP (energy) generation for cellular activities (the powerhouse of the cell)

Lysosome

Organelles that originate from the Golgi Apparatus and contain strong digestive enzymes (catalyze reactions that digest particles brought into the cell, worn-out organelles, and even the cell itself)

Nucleus

Control center of the cell that contains the genetic material

Cytoskeleton

An elaborate series of rods running through the cytosol, supporting cellular structures and providing the machinery to generate various cell movements

Cytoskeleton - Intermediate filaments

Rodlike structures that maintain the shape of organelles and the nucleus and give the cell mechanical strength

Cytoskeleton - Microtubules

The largest filaments

Hollow tubes that maintain the shape of the cell, hold organelles in place, move substances within the cell, and function in cell division

Cilia

Small, hairlike extensions that beat rhythmically together to propel substances past the cell

• Act like tiny brooms, removing debris that has been inhaled and trapped in mucus

Flagella

Single extensions that propel the cell itself (sperm cells are the only flagellated cells in the human body)

Centriole

Paired organelles found near the nucleus of the cell, active in cell division

• Microtubule organizing centers and are important in facilitating the assembly and disassembly of microtubules

Centrosome

Central area of the cell

Smooth Endoplasmic Reticulum

Lacks ribosomes

• Breakdown of stored glycogen

• Detoxification of drugs, certain pesticides and carcinogens

• Absorption, synthesis, and transport of fats

• Synthesis of steroid-based hormones such as sex hormones

• Stores calcium ions

• Lipid synthesis

• Lipid metabolism, cholesterol synthesis, and synthesis of the lipid components of lipoproteins

Rough endoplasmic reticulum

Performs some of the final steps of protein synthesis, modifying proteins the ribosomes have made

• Particularly integral membrane proteins and proteins secreted from the cell

Nucleolus

“Birthplace” of ribosomes

Dense spherical body in the cell nucleus involved with ribosomal RNA synthesis and ribosomal subunit assembly

Chromatin

A ball-like mass of tightly coiled DNA and proteins; RNA; and the nucleolus

Nuclear envelope

Double membrane that surrounds the nucleus

Nuclear pores

Holes in the nuclear envelope

Extracellular fluid

Fluid located outside the cells; includes interstitial fluid, blood plasma, and cerebrospinal fluid

Cytokinesis

The division of cytoplasm that occurs after the cell nucleus has divided

Plasma membrane structure

Phospholipids form a bilayer

Why do phospholipids form a bilayer in the plasma membrane?

The hydrophilic heads of the phospholipids are attracted to the water, while the hydrophobic tails are repelled by it. To minimize contact between the hydrophobic tails and water, they arrange themselves into a bilayer, with the tails facing each other in the interior and the heads exposed to the water on both surfaces. 

Diffusion

The movement of solute particles from a HIGH solute concentration to a LOW solute concentration until a state of equilibrium is reached

• Passive process - requires no net input of energy by a cell

Osmosis

The movement of solvent from a LOWER solute concentration to a solution with a HIGHER solute concentration

Isotonic

Iso = “same”

Extracellular fluid (ECF) has the same solute concentration as the cytosol

• Both have equal ability to cause osmosis

• No net movement of water into or out of a cell

• Solutions given by intravenous (IV) administration are almost always isotonic

Hypotonic

Hypo = “below”

Extracellular (ECF) has a lower solute concentration than the cytosol

• Cytosol has more solute particles, and has a greater ability to cause osmosis than the ECF

• Water will move into the cell by osmosis

• May cause cell to swell and burst

• Given as IV fluids when a patient has certain types of dehydration

Hypertonic

Hyper = “above”

ECF has a higher solute concentration than the cytosol

• ECF has a greater ability to cause osmosis

• Causes ECF to pull water molecules out of the cytosol by osmosis

• May cause cell to shrivel or crenate as it loses water to the ECF

• Only ever given by IV under very specific conditions

Interphase

When the cell is NOT dividing:

• G1

• S

• G2

Interphase - G1

Initial growth phase

• Cell grows, develops, and carries out activities specific to that cell type

Interphase - S

Cell’s DNA is replicated

• “S” stands for synthesis

Interphase - G2

Second growth phase which the cell makes its final preparations for division (mitosis)

Mitosis

• Prophase

• Metaphase

• Anaphase

• Telophase

Prophase

• Nuclear membrane starts to degenerate

• Chromatin condenses into individual chromosomes

• Mitotic spindle organizing around centrioles

• Centrioles have reaches opposite poles of the cell

• Spindle fibers emanate from each side of the mitotic spindle and attach to the centromere (one single fiber attaches to each side of the centromere)

Metaphase

Sister chromatids line up along the equator of the cell

Anaphase

• Spindle fibers shorten which pulls sister centromeres apart

• Sister chromatids migrate toward the opposite poles of the cell

• Cytokinesis begins

Telophase

• Cleavage furrow forms between the two cells

• Cell is pinched into two identical daughter cells and cytokinesis is completed

• Nuclear membrane begins to reassemble

• Mitotic spindle becomes less visible

• DNA returns to its chromatin form

Mitotic spindle

Made up of microtubules that facilitates the separation of chromosomes

• Ensures accurate chromosome segregation

Centromere

The point where sister chromatids are joined and where spindle fibers attach during cell division

• Ensures that sister chromatids are properly aligned and separating

• Ensuring each new cell receives the correct number of chromosomes

Metaphase plate

An imaginary line that runs across the cell, dividing the cell into hemispheres

Chromosome

Thread-like structure made of DNA and proteins

• Ensures accurate chromosome that the correct instructions are available for cell function and genes are passed down from one generation to the next

Centriole

Small, cylindrical organelle

• Forms spindle fibers that pull chromosomes apart

Spindle fibers

Long strands of protein that extend toward opposites sides of the cell

Chromatid

One of the two identical halves of a chromosome that has been replicated in preparation for cell division

• The two “sister” chromatids are joined at the centromere

Active Transport

Requires ATP to move

Brownian movement

Solute

Soluble

Solvent

Active transport

Filtration

Pinocytosis

Endocytosis

Semi-permeable membrane

Insoluble

Phagocytosis

Solution