A&P Lesson 3 - Cellular Form and Function

Organelles

the internal structures of a cell that carry out specialized metabolic tasks

What are the 2 main categories of organelles?

• non-membranous organelles

• membranous organelles

Non-membranous organelles

do not have a membrane surrounding them

• includes cytoskeleton, microvilli, centrioles, cilia, ribosomes, and proteasomes

Cytosol

a clear, viscous, watery colloid within the cell that contains enzymes, other proteins, amino acids, ATP, electrolytes, dissolved gases, and metabolic waste

Cytoskeleton

a network of protein filaments and cylinders

What are the functions of the cytoskeleton?

• structural support

• organizes cell content

• Directs movement of materials within cell and contributes to movement

What are the elements/components of a cytoskeleton?

microfilaments, intermediate filaments, and microtubules

Microfilaments

• smallest - 6nm thick

• made of actin protein

What are the functions of microfilaments?

• form terminal web

• provide mechanical strength by anchoring cytoskeleton to plasma membrane proteins

• interacts with cytosolic proteins to adjust liquidity of cytosol

• can interact with thick filaments for muscle cell contraction

If microfilaments make dense interactions, what happens to the cytosol?

it becomes dense and gelatinous

If microfilaments make dispersed interactions, what happens to the cytosol?

it becomes more fluid

Intermediate filaments

• 8-10 nm thick

• within skin cells

• made of protein keratin

What are the functions of intermediate filaments?

• give cell shape, strength/durability and resists stress

• stabilizes organelle position

• stabilized cell onto a substrate/other cells

Microtubules

• largest - 25 nm thick

• consists of protofilaments made of protein tubulin

What are the functions of microtubules

• dynamic and can readily assemble/disassemble

• maintains cell shape (changes to microtubules can change cell shape)

• holds organelles

• “highway system” - motor proteins can use ATP energy to move organelles that are attached to them along microtubule “tracks”

• makes axonemes of cilia and flagella

• forms mitotic spindle

• attaches to the centrosome

Microvilli

• extensions of the plasma membrane (1-2 um in length)

• core composed of microfilaments

• provide 15-40x more surface area to cells that have them

• best developed in cells specialized in absorption

• brush border

Cilia

• small hair-like processes 7-10 um long

• can be motile or non-motile

• beat in waves to sweep material across a surface

Where are cilia found?

• found in respiratory tract, uterine tubes, ventricles of brain, and ducts of testes

What is cilia composed of?

microtubules

How many cilia are found on each cell?

50-200

What is the difference between microvilli and cilia?

Microvilli - short and finger like Cilia - long and hair like

-1-2 nm -7-10nm

-add surface area -move material across cell

Centriole

a short cylindrical assembly of microtubules arranges in 9 groups of 3 microtubules each

What is the function of the centriole?

• play important role in cell division (mitosis)

• form spindle apparatus during mitosis

Ribosomes

small granules of protein and RNA responsible for producing proteins

• free ribosomes

• fixed ribosomes

What are the functions of the ribosomes?

• read the coded genetic messages in mRNA

• assemble amino acids into proteins

Where are ribosomes found?

in nucleoli, in cytosol, on outer surfaces of rough ER, and nuclear envelope

Free ribosomes

found in the cytoplasm to produce cytosolic proteins

Fixed ribosomes

attached to the endoplasmic reticulum; start off as free ribosomes

How do free ribosomes become fixed ribosomes?

mRNA attaches to the free ribosome, the ribosome can be signaled to attach onto the ER if destined

Proteasomes

• hollow, cylindrical organelles that dispose of surplus proteins

• contain enzymes (proteases) that break down tagged, targeted proteins into short peptides and amino acids

• can destroy tagged damaged cell proteins or viral proteins

Membranous organelles

surrounded by a membrane

• includes nucleus, endoplasmic reticulum (rough and smooth), Golgi complex, lysosomes, peroxisomes, and mitochondria

Membrane flow

continuous exchange membranes from one organelle to another via vesicles

Endoplasmic reticulum (ER)

network of interconnected membranous channels called cisterns

Rough ER

• parallel flattened sacs covered with ribosomes attached to its outside

• produces phospholipids and proteins of nearly all cell membranes

• synthesizes proteins that are packaged in other organelles of secreted from cell by exocytosis

Smooth ER

• tubular ER that lacks attached ribosomes

• synthesizes lipids and steroids

• detoxifies alcohol and other drugs

• calcium storage

Golgi complex

• a system of membranous cisterns that synthesize carbohydrates and modifies newly synthesized proteins

• sorts protein, splices some, adds carbohydrate moieties to some and packages them into membrane-bound Golgi vesicles

What happens to the Golgi vesicles?

some become lysosomes, some migrate and fuse to plasma membrane, and some become secretory vesicles

Lysosomes

package of enzymes bound by a membrane

What are the functions of lysosomes?

• intracellular hydrolytic digestion of substances

• can be used to break down invading bacteria or recycled damaged organelles

Primary lysosomes

formed by the Golgi complex, enzymes inside are inactive

Secondary lysosomes

formed when primary lysosome fuses to an endosome or damaged organelle which activates the enzyme

Autophagy

digestion of cell’s surplus organelles

Autolysis

digestion of a cell by itself; cell suicideL

Lysosomal storage disease

• > 30

• caused by lack of specific lysosomal enzyme which causes waste build up in cells

Tay-Sachs disease

rare genetic disease caused by lack of lysosomal enzyme which causes build up of lipids in brain cells causing them to die

Peroxisomes

resemble lysosomes but contain different enzymes; are produced by ER and mitochondria and from other peroxisomes

• present in all cells

Where are peroxisomes abundant?

kidney and liver

What are the functions of peroxisomes?

• use molecular oxygen to oxidize organic molecules

• neutralize free radicals, detoxify alcohol, other drugs and blood borne toxins

• break down fatty acids into acetyl groups for mitochondrial use in ATP synthesis

• reactions produce hydrogen peroxide (H2O2) but peroxisomes contain the enzyme catalase that breaks it down

Mitochondria

• organelles specialized for synthesizing ATP when oxygen is abundant

• change shape from spheroidal to thread-like

• surrounded by double membrane

• problems with mitochondria can cause metabolic disorders

Metabolic disorders

inherited from maternal side and cause problems with mitochondrial ATP generation; all cells in body are affected