[MOD1LEC] Organelles Of The Cell

What are the two types of living cells? How are they different from each other?

The two types of living cells are eukaryotic cells and prokaryotic cells

Eukaryotic cells contain a membrane-bound nucleus and membrane-bound organelles

Prokaryotic cells do NOT have a membrane-bound nucleus or membrane-bound organelles

What is considered the smallest individual unit of life?

The cell is considered the smallest individual unit of life

What are the tenets of the Modern Cell Theory?

• All organisms are composed of cells and cell products

• The cell is the simplest structural and functional unit of life. There are not smaller subdivisions of a cell or organism that, in themselves, are alive

• An organism’s structure and all of its functions are ultimately due to the activities of its cells

• All cells come only from pre-existing cells, not from nonliving matter

• The cells of all species have many fundamental similarities in chemistry, composition, and metabolic mechanisms

What are the three composite or generalized eukaryotic cell regions?

• The nucleus

• The cytoplasm

• The plasma membrane

Nucleus

• Control center of the cell

• Largest organelle

• Usually the only organelle visible with a light microscope

Nuclear envelope [Structures Of The Nucleus]

• Comprised of a phospholipid bilayer

• Contains nuclear pores that allow molecules and ions in and out of the nucleus, including

  • messenger RNA

  • ribosomes

  • enzymes

  • hormones

Nuclear pores [Structures Of The Nucleus]

Pores found on the nuclear envelope that regulate the movement of molecules and ions in and out of the nucleus, including

• messenger RNA

  • copy of DNA that exits the nucleus

  • is synthesized into protein

• ribosomes

• enzymes

  • travels from the cytoplasm to the nucleus
    
    

• hormones

  • activates certain genes

Nucleoplasm [Structures Of The Nucleus]

A jelly-like fluid containing the nucleolus, a spherical body made of RNA

The nucleolus produces ribosomes

Chromatin [Structures Of The Nucleus]

Latent chromosomes made of DNA and protein

• DNA contains the genetic code or blueprint

• mRNA is a copy of the DNA in the nucleus

Cytoplasm

The location of most cellular activities

Cytosol [Structures of the Cytoplasm]

Complex, semitransparent mixture made of 60-80% water plus dissolved solutes (soluble proteins, salts, and sugars)

Inclusions [Structures of the Cytoplasm]

Transient chemical substances

• stored nutrients like glycogen

• secretory products like mucus

• pigment granules such as melanin

• oil droplets

Ribosomes

The site of production of proteins, and the only organelle without a membrane

• Reads mRNA (copy of DNA from the nucleus) and assembles amino acids into proteins specified by the code

• The ribosomes that float around the cytoplasm make enzymes and other proteins for use within the cell

• Can be found in the nucleoli, cytosol, and surfaces of the nuclear envelope and rough ER

Endoplasmic reticulum

A branching network of membranes that occur throughout the cytoplasm

• Involved in intracellular communication

Rough endoplasmic reticulum

Contains ribosomes which accounts for its rough or grainy appearance

• Involved especially in protein synthesis, or creation of proteins that are going to be implemented in the process of exocytosis or lysosomes

Smooth endoplasmic reticulum

Contains no ribosomes, accounting for its smooth appearance

• Involved in processes such as

  • lipid synthesis

  • detoxification

  • calcium storage and release

    • found in liver cells

Golgi complex

Packages proteins received from the rough ER which are used inside and outside the cell for various functions

• Involved in the modification of newly synthesized proteins, lipids, and carbohydrates

• Synthesizes lysosomes and secretory vesicles

Golgi vesicles

Vesicles that may break off of the Golgi apparatus and become secretory vesicles

• Carry cell products to the cell surface for exocytosis

• Some become lysosomes

Vesicles

Membranous sacs or bags containing various substances for intracellular use and/or extracellular secretion

Lysosomes

Vesicles that contain powerful hydrolytic enzymes (enzymes that digest materials with water)

• Help destroy foreign substances entering the cell

• Involved in glucose mobilization

• Autophagy - digestion of worn out organelles

• Apoptosis - programmed cell death

Cytoskeleton

A group of microfilaments, intermediate filaments, and microtubules

• Form an internal scaffolding that holds organelles in place

• Gives shape to the cell

Microfilaments [Structures of the Cytoskeleton]

• Made of the protein actin

• Forms a fibrous mat outside of the cell called the terminal web that the phospholipid bilayer rests on, giving it structure

Intermediate filaments [Structures of the Cytoskeleton]

• Thicker and stiffer than microfilaments

• Give the cell its shape, resists stress, and attaches cells to neighboring cells

• Made of keratin in epidermal cells (fingernails and hair)

Epidermal means that it relates to the layer of skin known as the epidermis

Microtubules [Structures of the Cytoskeleton]

• Holds the organelles of the cell in place

• Forms bundles that help maintain the cells shape and rigidity

• Forms the axoneme (central core) of cilia and flagella

• Forms the mitotic spindle that guides chromosomes during cell division

These are not permanent structures, and can change locations throughout the cell as needed

Centrioles

A short, cylindrical assembly of microtubules

• Arranged in nine groups of three microtubules each

• Two centriole assemblies lie perpendicular to each other within a small area of the cytoplasm called the centrosome

Centrioles play a role in cell division

Cilia and flagella

Hair-like motile projections from free surfaces that help propel substances within body or allow movement

• Cilia are usually shorter and more numerous, and move mucus, ova, etc.

• Flagella are usually longer and less numerous

Plasma membrane

The cell and many of the organelles within it are bordered by a plasma membrane

• Establishes boundary, shape, and identity of the cell

What processes occur at the surface of a cell’s plasma membrane?

• Immune processes

• Binding of the egg and sperm

• Cell-to-cell signaling by hormones

• Detection of tastes and smells