LECTURE 2 (Cells: Structure and Function)

Every cell has three things in common:

  1. Metabolic functions (using sugars, oxygen, etc)
  2. Responds to its environment
  3. Capable of maintaining homeostasis within itself and within the body.

HOMEOSTASIS is maintaining a constant and appropriate internal environment, such as temperature, pH, glucose levels, etc.

•Plasma membrane (actually, a type of organelle)

•Cytoplasm and cytosol

•Nucleus

•Organelles (a membranous or membrane-bound compartment that carries out particular functions)

•Ribsomes (little factories that take amino acids and make proteins out of them)

CYTOPLASM: watery liquid found inside and outside the organelles, but outside the nucleus.

CYTOSO: Lanother liquid that is thicker than water, and is NOT inside the organelles. It is only found outside of the organelles and nucleus.

Contains the following:

a. Mostly water

b. Things dissolved in water (amino acids, sugars like glucose, nucleic acids, and ATP, which is a molecule used for energy).

c. Cytoskeleton

Cytoskeleton: made up of long protein fibers, extend throughout cytosol.

Function of cytoskeleton:

1) Maintains cell shape

2) Movement (such as muscle cell contraction, organelles within the cell, or the cell itself moving around).

ORGANELLES: those that are surrounded by a membrane

  • PLASMA (CELL) MEMBRANE
  • ENDOPLASMIC RETICULUM (ER): a network of channels.
  • ROUGH ENDOPLASMIC RETICULUM (endoplasmic = within
  • SMOOTH ENDOPLASMIC RETICULUM (no ribosomes)
  • GOLGI COMPLEX
  • VESICLES (vacuoles)
  • MITOCHONDRIA
  • NUCLEUS
  • CENTRIOLES

PLASMA (CELL) MEMBRANE

Surrounds the entire cell.

Functions of the Plasma Membrane:

  1. Movement of materials into and out of cell, acts as a barrier to the external environment
  2. Acts as a site for receiving signals from the rest of the body
  3. Acts as a site for holding the cell in place

The plasma membrane is made up of two layers of molecules = PHOSPHOLIPIDS (Phospho-lipied Bilayer)

RIBOSOMES

Ribosomes make proteins.

Ribosomes are not organelles because they do not have a plasma membrane.

ENDOPLASMIC RETICULUM (ER):a network of channels.

•Two types:

•Rough ER: contains ribosomes

•Function of ribosomes is to make proteins.

•Smooth ER: no ribosomes

•Function is to detoxify chemicals that enter the cell.

ROUGH ENDOPLASMIC RETICULUM (endoplasmic = within cytoplasm; reticulum = network; rough = surface of membrane covered with ribosomes. This is an organelle, but the ribosomes are not.

Function of RER is the synthesis (making) of certain kinds of proteins:

a. Membrane proteins

  1. Proteins for export (such as digestive system enzymes)
  2. Proteins for use within the cell

SMOOTH ENDOPLASMIC RETICULUM(no ribosomes)

Function of SER

a. SER is continuous with the rough ER, but lacks ribosomes and

functions primarily in lipid production

b. Involved in metabolism (makes/ breaks) of carbohydrates (sugars)

and lipids.

  1. Stores calcium (necessary for every cell)
  2. Detoxifies harmful substances (alcohol, drugs, etc)

GOLGI COMPLEX

Functions of Golgi complex:

  1. Packages the proteins made by the RER and sends them where they need to go (like a FedEx center!)
  2. Sometimes proteins are modified in the golgi complex.Therefore, this structure receives materials from the rough ER and “packages and ships” them.

VESICLES (vacuoles): a sphere of membrane with something in it. Bubble-like containers for various substances. This is an organelle. Some are created by the end of the Golgi complex: a piece of membrane pinches off, leaving a protein in the vesicle, which carries the protein to the cell membrane, where it merges with the cell membrane, pops, and releases its contents outside of the cell.

Many types.

Lysosomes

Transport vesicles

Storage vesicles

LYSOSOMES: are sacs of powerful digestive enzymes to dissolve an old organelle, etc, or to commit cell suicide = APOPTOSIS (programmed cell death).

-Specialized vacuoles that contain digestive enzymes and acids that dissolve foreign bodies that enter the cell.

-When bacteria enter a cell, the lysosome will fuse w/the bacteria and release its enzymes on them to destroy them.

TRANSPORT VESICLES: when material needs to move from RER to Golgi complex, or from Golgi complex to cell membrane, etc.

STORAGE VESICLES

MITOCHONDRIA

  • Function of mitochondria is to make ATP, which is cellular energy (ATP is an energy source).

NUCLEUS

NUCLEUS

NUCLEOLUS

  • Within a nucleus there sometimes are areas that are darker. These are regions of condensed RNA.
  • The nucleolus is NOT an organelle, but the nucleus is. Don’t get “nucleolus” mixed up with the word “nucleus” on the test. The nucleolus does not contain the DNA; the nucleus does.The nucleolus is within the nucleus, but it does NOT contain DNA.
  • The nucleolus makes ribosomes and stores RNA (RNA is made in the nucleus). RNA is important for protein synthesis.

TRANSCRIPTION is the process of DNA communicating with RNA.

•This occurs in the nucleus.

•TRANSLATION is the process of RNA communicating with a ribosome to tell it what type of protein to make. Therefore, translation is characterized by PROTEIN SYNTHESIS.

•Thisoccurs in the cytoplasm.

CENTRIOLES

Centrioles are filaments within the cell that function during mitosis.

•When the cell goes from metaphase to anaphase of mitosis, the chromatids separate and follow the spindles of the centrioles towards the opposite ends of the cell.

FLAGELLUM

•Some cells have a flagellum, which is a whip-like tail used to help them move.

•An example is a sperm cell.

MICROVILLI

•Some cells have microvilli, which increase the surface area of cells by approximately 600 fold, thus facilitating absorption and secretion.

CILIA

•Some cells have cilia, which are small, hair-like structures that can wave back and forth, causing substances to move along across the top of the cell.

•For example, the cells of the lungs are lined with cilia, which move mucous up from the lungs so it can be coughed up and swallowed.

STEM CELLS: A population of cells are always available to replace the cells that died

  • Muscle stem cells give rise to new muscle cells.
  • Bone marrow stem cells give rise to new blood cells.
  • Embryonic stem cells give rise to any type of cells, including neurons (adults don’t have neural stem cells) and pancreatic cells (diabetics don’t have pancreatic stem cells).
  • Stem cells are named by type + suffix: BLAST
  • Erythrocyte = RBC. Erythroblast = stem cell that gives rise to erythrocyte.

Too many cells can be a TUMOR (an abnormal growth). Two types of tumors:

  1. BENIGN(“harmless”, although can cause harm by pressing on vital structure)
  2. MALIGNANT (cancerous). These are dangerous because the cells in the tumor METASTASIZE(leave original site, go elsewhere and grow).

Cancer is hundreds of diseases, each with a different cause, symptoms, treatment, and prognosis. Any cell type can become malignant, producing different types of cancer.

THREE TYPES OF CANCER

  1. CARCINOMA: epithelial tissue
  2. SARCOMA: Connective tissue
  3. LEUKEMIA: Blood or blood-forming tissues

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