Biology 107Biology 107

Cell IICell II

September 24, 2004September 24, 2004

Cell IICell II

Student Objectives:Student Objectives: As a result of this lecture and the assigned As a result of this lecture and the assigned reading, you should understand the following:reading, you should understand the following:

1.1. Ribosomes are non-membranous organelles that are the sites of Ribosomes are non-membranous organelles that are the sites of synthesis of proteins in the cell. synthesis of proteins in the cell. RibosomesRibosomes consist of two consist of two subunits, the large and the small, comprised of proteins and subunits, the large and the small, comprised of proteins and specific RNAs, called rRNAs (ribosomal RNAs). The mRNA and specific RNAs, called rRNAs (ribosomal RNAs). The mRNA and the amino acids with their carriers (tRNAs or transfer RNAs) bind the amino acids with their carriers (tRNAs or transfer RNAs) bind to ribosomes, and polypeptide chains are formed by dehydration to ribosomes, and polypeptide chains are formed by dehydration synthesis. synthesis.

2.2. Ribosomes may be attached to membrane or "free" (non-Ribosomes may be attached to membrane or "free" (non-membrane attached) in the cytoplasm.membrane attached) in the cytoplasm.

Cell IICell II3.3. Endoplasmic reticulum is a membranous organelle that may be Endoplasmic reticulum is a membranous organelle that may be

subdivided into two different types with different functions.subdivided into two different types with different functions.

a.a. Rough endoplasmic reticulum (Rough endoplasmic reticulum (RERRER) is so named because it is ) is so named because it is studded with ribosomes. RER functions to make proteins for studded with ribosomes. RER functions to make proteins for secretion secretion by the cell or for incorporation into cellular membranes. The by the cell or for incorporation into cellular membranes. The RER also RER also begins the compartmentalization and processing of some begins the compartmentalization and processing of some proteins proteins so they can be shipped out of the cells or distributed to so they can be shipped out of the cells or distributed to specific specific subcompartments.subcompartments.

b.b. Smooth endoplasmic reticulum (Smooth endoplasmic reticulum (SERSER) is a series of ) is a series of interconnected interconnected membrane tubules that lack ribosomes. SER and RER membrane tubules that lack ribosomes. SER and RER are are continuous. One of the functions of ER lacking ribosomes is the continuous. One of the functions of ER lacking ribosomes is the

synthesis of lipids, including phospholipids, fats and steroids. synthesis of lipids, including phospholipids, fats and steroids. SER SER also contains enzymes that are involved in detoxification, and in also contains enzymes that are involved in detoxification, and in some some cells SER is involved in calcium storage and release.cells SER is involved in calcium storage and release.

Cell IICell II4.4. The The Golgi apparatusGolgi apparatus is a stack of flattened membrane sacs, but is a stack of flattened membrane sacs, but

they are not interconnected like ER stacks. Golgi receives, they are not interconnected like ER stacks. Golgi receives, modifies and segregates different proteins.modifies and segregates different proteins.

a.a. Some of the proteins modified and sorted by the Golgi are Some of the proteins modified and sorted by the Golgi are parts of membranes (such as channel proteins or parts of membranes (such as channel proteins or

receptor receptor molecules), some of the proteins are secreted, molecules), some of the proteins are secreted, and some of the and some of the proteins are routed to other organelles proteins are routed to other organelles (e.g., lysosomes).(e.g., lysosomes).

b.b. Within the Golgi are enzymes to add sugar molecules, Within the Golgi are enzymes to add sugar molecules, sulphate sulphate groups and phosphate groups to proteins.groups and phosphate groups to proteins.

c.c. Specific chemical modifications help tag and sort Specific chemical modifications help tag and sort molecules molecules through the Golgi into different destination through the Golgi into different destination streams.streams.

Cell IICell II5. Vesicles are relatively small membrane sacs that function to

shuttle materials around the cells and between the cell surface and the membranous organelles. For those membranous organelles that do not have direct membranous continuity, vesicles provide indirect, functional continuity through pitching off, movement to a new site, fusion and transfer of materials. This shuttling system has directionality and provides points of control of passage. When vesicles fuse with a new membrane system they are adding not only contents but also membrane.

6. The lysosomes are membrane-bounded sacs (vesicles) that contain hydrolytic (digestive) enzymes necessary for the normal turnover of cell components. The membrane enclosure of the hydrolytic enzymes keeps these enzymes from destroying the cell.

Ribosomes Consist of Large Ribosomes Consist of Large and Small Subunitsand Small Subunits

Ribosomes May be “Free” or Ribosomes May be “Free” or Bound to ER MembraneBound to ER Membrane

RER Contains Bound RER Contains Bound RibosomesRibosomes

RER Synthesizes Integral Membrane RER Synthesizes Integral Membrane Proteins, Lysosomal Proteins, and Proteins, Lysosomal Proteins, and Proteins for Secretion from the CellProteins for Secretion from the Cell

Endoplasmic Endoplasmic Reticulum Reticulum

(ER)(ER)Rough endoplasmic reticulum Rough endoplasmic reticulum (RER) is involved in protein (RER) is involved in protein synthesissynthesis

Smooth endoplasmic Smooth endoplasmic reticulum (SER) is involved in reticulum (SER) is involved in lipid synthesis, breakdown of lipid synthesis, breakdown of certain toxins, and calcium certain toxins, and calcium sequestrationsequestration

Golgi ApparatusGolgi Apparatus

Golgi Apparatus Processes and Sorts Golgi Apparatus Processes and Sorts Materials it Receives from the RERMaterials it Receives from the RER

Lysosomes Contain Hydrolytic Lysosomes Contain Hydrolytic EnzymesEnzymes

Example of Pathway for Proteins Example of Pathway for Proteins Synthesized in RER and Synthesized in RER and

Processed/Sorted in the GolgiProcessed/Sorted in the Golgi

Synthesis and Processing of Synthesis and Processing of Lysosomal ProteinsLysosomal Proteins

Cellular TraffickingCellular Trafficking

Cellular TraffickingCellular Trafficking