Cell Structures

The Nucleus

• nuclear envelope contains nuclear pores for some things to enter and exit (nucleoplasm within)
• chromatin is DNA and proteins, when the cell begins to divide, chromatin condenses and forms chromosomes
• DNA remains in the nucleus, it sends instructions to the cytoplasm via messenger RNA
• RNA directs the synthesis of proteins on ribosomes in the cytoplasm
• Nucleolus assembles ribosomes within the nucleus, ribosomes contain the "tools" to construct proteins

Endoplasmic Reticulum -- Transport System

(endoplasm means "within cytoplasm", reticulum means "little net"
--divides cell into compartments
--channels molecules through the cell's interior, like a little highway

Rough ER
--has ribosomes which give it its "rough" appearance
--functions in protein synthesis
--ER transports newly assembled proteins to the Golgi Apparatus

Smooth ER
--mostly contains enzymes that unction in lipid synthesis (such as hormones like estrogen and testosterone)

Golgi Apparatus -- Delivery System    

• flattened stacks of membranes
• functions in collection, packaging and distribution of molecules made in the cell and used elsewhere
• front end (cis) faces the ER, and the back end (trans) faces the cell membrane
                --the folded stacks are called cisternae
• unprocessed proteins enter the Golgi apparatus from ER
               proteins are packaged and exported near membrane

Jobs of the Golgi Apparatus (aka Golgi Complex)

• separates proteins according to their destinations
• modifies proteins (adds sugar and makes glycoproteins)
• packages materials into vesicles which are exported outside the cell  -  secretion

Lysosomes - Intracellular Digestion Centers

• vesicles that are used to digest
• contain high levels of degrading enzymes   (to "lyse" means to dissolve)
• recycle old and worn out cell parts
• "suicide sac" -  apoptosis
• digest other particles taken in by phagocytosis
• -this "food" is stored in food vacuoles, the lysosomes fuse with the vacuoles and release digestive enzymes
• found in animal cells

 TAY-SACHS disease – missing an enzyme of the lysosomes that breaks down a fatty substance.  Over time this fat builds up in the brain and nervous tissue, smothering the cells.  Results in degeneration and death.

Ribosomes - Sites of Protein Synthesis

--each is composed of two subunits, one large and one small
--mRNA is "read" by the ribosomes and amino acids are assembled into proteins
--ribosomes are manufactured by the nucleolus inside the nucleus
--polyribosomes – strings of ribosomes in the cytoplasm that work to make a protein

Other Organelles

-- Peroxisomes – result in hydrogen peroxide, broken down by catalase
-- Vacuole  --  mainly storage or specific functions (contractile vacuole)
-- Plant cells have a CENTRAL VACUOLE  - used for storage and help to maintain hydrostatic pressure

ENERGY RELATED ORGANELLES

Mitochondria - The Cell's Chemical Furnaces

--contains its own DNA, support for Endosymbiosis Theory
--singular is "mitochondrion"
--2 membranes, one smooth outer membrane, and an inner membrane folded into layers called cristae
--Cristae has two compartments: the matrix and the intermembrane space
--mitochondria divide before cell division, they are not synthesized like other cell parts
--function to store energy for cell use. Energy is stored in the form of ATP - adenosine triphosphate

 

Chloroplasts - Where Photosynthesis Takes Place

--only found in plant cells
--has its own DNA, like mitochondrion
--functions to convert light energy to carbohydrates
--carbohydrates then broken down in mitochondria to produce ATP
--consists of grana, closed compartments that are stacked
--thylakoids are the individual disk shaped compartments that make up the grana (stack of thylakoids)
--stroma is the fluid surrounded the thylakoids

*Chloroplasts are a type of plastid
Chromoplasts – red, yellow and orange pigment
Leucoplasts – colorless (potatoes)

 

Cytoskeleton - Support System

• Microfilaments (now called actin filaments) – occur in bundles, form tracks within the cell for the movement of organelles,  used to form pseudopods (ameba)
• Intermediate filaments  - support membrane, cell to cell junctions
• Microtubules -  (little pipe) – regulated by the MTOC (microtubule organizing center), radiate from the centrosome   -  form the spindle during cell division
• Centrioles – used during cell division to move and separate chromosomes, only found in animal cell

Related to Movement

Pseudopod – extensions of the cell that allow for movement (ameba), depend on actin filaments

Cilia (hair)

Flagella (whip)
--function in movement
-- 9+ 2 Arrangement of microtubules