Cell Organelles and Functions

• Major cell features include organelles, each with specific functions.

Cell Organelles and Functions

• The plasma membrane controls the entry and exit of substances.
• Cytoplasm is the semi-fluid matrix that suspends organelles.
• The nucleus houses DNA and directs cell activities.
• The cytoskeleton provides shape, movement, and support.
• Mitochondria produce ATP (energy) and contain cristae, they are involved in apoptosis (programmed cell death).
• Ribosomes are the site of protein synthesis.
• The endoplasmic reticulum (ER) modifies proteins (rough ER, contains ribosomes), synthesizes lipids, and detoxifies (smooth ER, no ribosomes).
• The Golgi body modifies, sorts, and packages proteins and lipids.
• Vesicles transport materials within the cells
• Lysosomes are digestive organelles containing enzymes.

Cell Size and Surface Area-to-Volume Ratio

• Cells vary, but cannot exceed the volume that can be nourished by materials passing through the surface membrane.
• A physical relationship dictates the small size of cells, known as the surface area-to-volume ratio.
• As a cell enlarges, surface area increases slower than volume, decreasing the SA:Vol ratio.

Prokaryotic versus Eukaryotic cells

• Prokaryotic cells contain "Pro (before) karyotic (nucleus)", they do not have a nucleus.
• Eukaryotic cells contain "Eu (true) karyotic (nucleus)", they have a true nucleus and have other organelles present.
• The largest difference between cell types is the presence or absence of a nucleus.
• Prokaryotic cells (bacteria and archaea) lack membrane-bound organelles, but do have ribosomes.
• Eukaryotic cell DNA is contained within the nucleus.
• Examples of eukaryotic cells include animal, plant, fungi, and protist cells.
• Prokaryotic cells are structurally simpler and typically smaller than eukaryotic cells.
• Eukaryotic cells are structurally more complex, typically larger, and found in plants, animals, fungi, and protists.

Plasma Membrane Structure and Function

• The plasma membrane is the outer boundary of the cell.
• The plasma membrane controls substance movement in and out of the cell.
• The phospholipid bilayer separates extracellular fluid from the cell's cytoplasm.
• Membrane components include proteins, cholesterol, and carbohydrates, giving it the qualities of a fluid mosaic.

Main Membrane Components

• Five main components of the membrane exists.
• Phospholipid bilayer has a phosphate head, which is hydrophilic, and a fatty acid tail, which is hydrophobic, and it controls what passes through the membrane.
• Cholesterol, a lipid steroid, helps maintain proper fluidity and how freely components move within the membrane.
• Proteins transport, support, communicate, and recognize.
• Glycoproteins are chains of sugars attached to a protein that function as attachment sites and in cell recognition.
• Glycolipids are chains of sugars attached to a lipid that also function as attachment sites and in cell recognition.

Labeling the Membrane

• Cytoplasm and extracellular fluid are different, with proteins and fluids specific to the cell.
• Carbohydrates exist on the exterior of the membrane.
• Cholesterol and surface proteins are interspersed throughout.
• Filaments of the cytoskeleton and embedded proteins also exist across and within the membrane.
• There are several membrane layers, the plasma membrane, phospholipid bilayer, glycoprotein and glycolipid.

Membrane Permeability

• Hydrophobic compounds (non-polar), some gasses (oxygen, carbon dioxide), and very small uncharged molecules pass freely through the membrane.
• Water is polar, yet small, allowing for some membrane permeability.
• Hydrophilic (polar compounds) larger than water) and ions/charged compounds cannot pass freely.

Molecular Transport Mechanisms

• Passive transport does not require energy, following the concentration gradient (high to low).

Passive Transport Subtypes

• Simple diffusion is where freely passing molecules through the membrane are controlled by concentration gradient with O2, CO2, uncharged molecules, hydrophobic molecules.
• Facilitated diffusion is aided by transport proteins, still controlled via concentration gradient with water-loving molecules like glucose, amino acids, or charged molecules/ions.
• Osmosis is the movement of water across a selectively permeable membrane from high to low water concentration.
• Water is drawn toward higher solute concentration.

Active Transport

• Active transport requires energy and goes against the concentration gradient (low to high).
• Active transport transports polar or charged items with assistance of a carrier protein and energy (usually from ATP).

Vesicle Transport

• Endocytosis moves things into the cell using a vesicle.
• Three types of moving include, phagocytosis of large particles, pinocytosis of fluids, which receptor-mediated endocytosis uses receptors to bring in specific molecules.
• Exocytosis moves things out of the cell using a vesicle.

Solute Concentration Solutions

• Hypertonic solution (high solute outside cell) causes water to leave the cell, and the cell shrinks.
• Isotonic solution (equal solute inside and outside) causes the cell to gains and loses water at the same rate, maintaining its physical shape.
• Hypotonic solution (low solute outside cell) causes the cell to gain more water than it loses and swells.

Lysosomal Enzyme Disorder

• Tay-Sachs is a hereditary disease that inhibits the ability to break down lipids in nerve cells due to a missing enzyme normally found in lysosomes.

Cytoskeleton Function

• Microtubules make up cilia, flagella, and centrioles.
• Microfilaments are important for muscle contraction, pseudopodia movement, and cell division.
• Intermediate filaments maintain cell shape and anchor organelles.

Definition of Terms

• Concentration gradient defines the difference between a concentration of a substance on each side of a membrane.
• Hydrophobic compounds are water hating (lipophilic).
• Non-polar refers to hydrophobic (non-polar) molecules.
• Hydrophilic compounds are water loving (lipophobic).
• Plora; refers to hydrophilic (polar compounds) larger than water.
• Passive transport does not require energy, and uses a concentration gradient, from high to low concentration.
• Active transport and does require energy and goes against the concentration gradient, from low to high concentrations.
• Simple diffusion is where freely passing molecules through the membrane are controlled by concentration gradient (from high concentration to low concentration).
• Facilitated diffusion uses a transport protein, still controlled by concentration gradient.
• Osmosis occurs with the movement of water across a selectively permeable membrane from a high to low water concentration.
• Exocytosis is moving things out of the cell using a vesicle.
• Endocytosis is moving things into the cell using a vesicle.
• Phagocytosis occurs when cells transport large particles and cells (bacteria) into the cell using vesicles.
• Pinocytosis is when cells transport fluid into the cell using vesicles.
• Receptor-mediated endocytosis occurs when membrane receptors are involved.
• An organelle is a membrane-bound internal compartment in cells for specialized functions.
• The nucleolus is a dense area in the nucleus where ribosomes are produced.
• The nuclear envelope is a double membrane (two different bilayers) that surrounds the nucleus.
• Nucleoplasm is the area residing inside the nucleus.
• Chromosomes are composed of DNA wrapped around proteins, this material is called chromatin.
• Chromatin consists of DNA and its associated proteins.
• Cristae refers to an inner membrane fold = cristae that increases surface area for cellular respiration.
• Apoptosis is defined as programmed cell death.