AP Bio A Tour of the Cell

Nucleus

• Structure

  • DNA and protein surrounded by a nuclear membrane
  • Contains nuclear pores, nuclear lamina, and a nucleolus

• Nuclear membrane

  • Also called the nuclear envelope.
  • Double membrane
  • Porous

• Nuclear lamina

  • A protein network that stabilizes the nucleus
  • Found just inside the nuclear membrane.

• Functions

  • Control center of the cell
  • Contains DNA
  • Directs protein synthesis
  • Contains genetic material

• Nucleolus

  • Small dark region of the nucleus.
  • Place where ribosomes are made.

Other notes

• DNA is found in the form of chromatin
  • thin and uncoiled
  • chromosomes only form when a cell divide

Ribosomes

• Structure

  • Made of rRNA and protein.
  • Made in the nucleolus, assembled in the cytoplasm.
  • 2 subunits
  • Large subunit
  • Small subunit

• Functions

  • Help assemble proteins using the genetic code.
  • Assemble when a protein is being formed.

• Other notes

  • Can be found free floating in the cytoplasm or bound to the rough endoplasmic reticulum.
  • Found in higher numbers in cells that are responsible for making a lot of proteins.

Endoplasmic reticulum

• lumen (cisternal space): the internal compartment of the ER

• Rough E.R.

  • Structure

  • studded network of membranes with ribosomes on the outer surface

  • Functions

  • makes secretory proteins (glycoproteins)

  • grows in place by adding membrane proteins and phospholipids to its own membrane

  • makes membrane phospholipids

  • transports proteins

• Smooth E.R.

  • Structure

  • smooth network of membranes because it lacks ribosomes

  • Functions

  • synthesis of lipids

  • metabolism of carbohydrates

  • detoxification of drugs and poisons

  • storage of calcium ions

  • make steroids

Golgi Apparatus (Complex, Body)

• Structure

  • The Golgi apparatus consists of flattened membranous sacs (cisternae) that look like a stack of pita bread. There can be hundreds in a cell.
  • The membrane of each cisterna in a stack separates its internal space from the cytosol.
  • Vesicles concentrated in the vicinity of the Golgi apparatus are engaged in the transfer of material between parts of the Golgi and other structures.
  • A Golgi stack has distinct structural directionality, with membranes of cisternae on opposing sides of the stack differing in thickness and molecular composition.
  • The two opposing sides of a Golgi stack are referred to as the Cis Face and the Trans Face.

• Cis Face

  • Usually located near the ER. Transport vesicles move material from the ER to the Golgi Apparatus.
  • A vesicle that buds from the ER can add it's membrane and the contents of it's lumen to the Cis Face by fusing with a Golgi membrane.
  • Known as the "receiving side" of the Golgi apparatus.

• Trans Face

  • The trans face is where they exit in the form of smaller detached vesicles
  • Vesicles filled with processed lipids and proteins bud off from the trans face.

• Functions

  • Responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations such as lysosomes, the plasma membrane, or secretion
  • Manufactures some macromolecules, as many polysaccharides secreted by cells are Golgi products. Pectins and other non cellulose polysaccharides are made in the Golgi of plant cells and incorporated into the cell walls along with cellulose.

Lysosomes

• Structure

  • membranous sac of hydrolytic enzymes
  • circular

• Functions

  • eukaryotic cells use lysosomes to digest (hydrolyze) macromolecules
  • lysosomal enzymes work best in the acidic environment found in lysosomes x
  • It is the digestive system of the cell serving both to degrade material taken up from outside the cell and to digest obsolete components of the cell itself.

• Other notes

  • Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the golgi apparatus for further processing
  • Apoptosis seems to be dependent on lysosomal proteases, which need to be released into the cytosol for apoptosis to be efficient.
  • Apoptosis is the death of cells which occurs as a normal and controlled part of an organism's growth or development.

Vacuoles

• Types
  • Central
  • Contractile
  • Food

Central Vacuole

• Structure

  • surrounded by membrane called tonoplast
  • largest organelle in the cell
  • consists of cell sap and tonoplast

• Functions

  • act as a storage space for water and other molecules in the cell
  • develops by the coalescence of smaller vacuoles

• Other Notes

  • Turgor pressure is the pressure exerted by a water-filled central vacuole against the cytoplasm and other organelles of the cell

Contractile Vacuole

• Structure

  • membrane makes contract and then water squeezes water out

• Functions

  • controls the intracellular water balance by accumulating and expelling excess water out of the cell, allowing cells to survive under hypotonic stress as in pond water.

Food Vacuole

• Structure

  • composed of single layered membrane
  • found in cytoplasm of plants, animals, and protists
  • surrounded by thin membrane and filled with fluid and any particles they take in

• Function

  • store cellular fuel

• Other Notes

  • When a cell wants to digest the food inside a vacuole, the vacuole merges with lysosomes

Mitochandria

• Structure

  •  oval-shaped with two membranes (an outer and inner membrane), found in cytosol of a cell

• Parts

  • ==Cristae== - folds in the inner membrane which increase the surface area of the mitochondria → creates more space for chemical reactions
  • ==Matrix== - gel-like substance
  • DNA is found in offspring inherit mitochondrial DNA solely from the mother
  • Inner membrane space - small lumen (inside space of tubular structure) between the outer and the inner mitochondrial membranes

• Functions

  • Involved in breaking down sugars and fats into energy through cellular respiration
  • This metabolic process creates ATP
  • ATP - the energy source of a cell through a series of steps that require oxygen

• Other Notes

  • Mitochondria do not contain anywhere near the amount of DNA needed to code for all mitochondria-specific proteins, however, a billion or so years of evolution could account for a progressive loss of independence
  • mitochondria is the powerhouse of the cell
  • Found in almost all eukaryotic cells
  • Mitochondria is constantly being recycled by the cell

Plastids

• Choloroplasts

  • Structure

  • Made up of 3 compartments: the intermembrane space, stroma, and the thylakoid space

  • Has a round or disk-shaped body

  • Thylakoid membrane

  • membranous system in the form of flattened, interconnected sacs

  • often in interconnected stacks called grana

  • used to convert light energy into chemical energy

  • Stroma

  • fluid outside the thylakoid

  • contains chloroplast DNA, ribosomes, and many enzymes

  • Involved in the synthesis of organic molecules from carbon dioxide and water

  • Functions

  • An organelle found in plants and photosynthetic protists that absorbs sunlight 

  • Uses it to drive the synthesis of organic compounds from carbon dioxide and water.