BCMB Ch. 4 - Cellular Structure and Function

difference between the cytosol and cytoplasm

cytoplasm contains the contents of the cell including the organelles vs. The cytosol contains the contents of the cell NOT including the organelles

Phospholipid Bilayer (plasma membrane) function

• Regulating the passage of substances into and out of the cell as well as between organelles and the cytosol (the organelles are surrounded by plasma membranes)

• Detecting chemical messengers at the cell surface

• Linking adjacent cells together

• Anchoring cells to the extracellular matrix

phospholipid

formed when two fatty acid chains and a phosphate group bind to glycerol, polar heads can interact with water, Non-polar heads cannot

Integral membrane proteins (transmembrane proteins)

• Extend from one side of the membrane to the other (connecting the inside and outside of the cell)

• Amphipathic: it has both hydrophobic and hydrophilic properties

Peripheral membrane proteins

• Only reach one side of the membrane surface

• Not amphipathic

Most transmembrane proteins cross the membrane ___ times

7

Membrane junctions

allow adjacent cells to communicate with one another by connecting their plasma membranes

integrins

transmembrane proteins that bind to other proteins in the extracellular matrix and connect them to nearby cells

Types of junctions

• Desmosomes

• Tight Junctions

• Gap Junctions

The plasma membranes of adjacent cells do NOT touch, but remain very close together, about _____ nanometers

20

cadherins

hold the cells close together so that they can communicate

desmosomes

found in areas that are subject to stretching (i.e. the skin) and they hold the cells together

tight junctions

• formed when two adjacent cells are sitting next to each other and physically touching

• Held together by protein complexes

• No pore is present

• Located in areas where it is important to limit the movement of particles- i.e. the lining of the bladder and intestine

Gap Junctions

• Protein channels that connect the cytosols of adjacent cells

• In a sense makes the cells act like one giant cell

• Found in electrical synapses

Glycoproteins

• Sugar/protein complexes on the outside of the cell

• Markers that other cells what type of cell they are

• One of the reasons cancer is so difficult to treat

Nucleus

• Store and protect genetic material so that it can be used to make proteins and passed on to future generations of cells

• When the cell is not preparing to divide, the nucleus is a mess of uncoiled DNA

DNA Condensation

• DNA is wrapped around proteins called histones

• Histones clump together to form clusters called coils

• Coils continue to condense until the final chromosome is formed

Nuclear envelope

• Surrounds nucleus

• Contains holes called nuclear pores, which allow for the passage of materials in and out

Ribosomes

• Clusters of proteins and RNA

• The site of protein synthesis

• Some are found floating in the cytosol, while most are attached to the endoplasmic reticulum (ER)

Endoplasmic Reticulum

• A network of membranes, folded many times

• Two main types, rough and smooth

Rough ER

Contains ribosomes. The ribosomes give it a sandpaper-like or ROUGH appearance. This is where most proteins are made. Proteins can also be modified here after production

Smooth ER

Does NOT contain ribosomes, thus it has a smooth appearance. This is where lipids are made. It can also store calcium and release it to aid in muscle contraction

Golgi Apparatus

• A series of flattened membranous sacs

• It receives proteins and lipids made in the ER and modifies them

• Sorts the proteins and packages them into secretory vesicles for release out of the cell

Mitochondria

• Make ATP through respiration

• Elongated bean-like structures made up of folded membranes- this allows for a greater surface area to make more ATP

• Found in large numbers throughout the cytoplasm

Lysosomes

• Spherical or oval shaped organelles surrounded by a single membrane

• Contain an acidic solution and digestive enzymes

• Break down bacteria and debris from dead cells and damaged organelles

• GARBAGE MEN OF THE CELL

• A cell can contain several hundred lysosomes

Peroxisomes

• Oval-shaped organelles surrounded by a single membrane

• Break down lipids, alcohol and toxic substances by using the electronegative oxygen to remove the positively charged hydrogen from molecules

• Product is hydrogen peroxide H2O2

• Can break down lipids to create ATP

Cytoskeleton

Structural filaments that can create movement and alter cell shape, important in cell division

3 Main types of filaments

Actin filaments, intermediate filaments, microtubules

Actin Filaments

• Can be assembled and disassembled rapidly

• Smallest filament (only about 7 nanometers)

• Made up of a protein called Gactin

• Involved in cell movement

Intermediate Filaments

• More difficult to disassemble

• 10 nanometers in size

• Made up of several different proteins including keratin, desmin and lamin

• They anchor the nucleus and provide strength

Microtubules

• Can be assembled and disassembled rapidly

• The largest filament (about 25 nanometers)

• Made up of a protein called Tubulin

• Hollow tubes that help to give neurons their long structure

Cilia

• Hair-like extensions on the surface of the cell

• Have a central core made up of microtubules

• Line some epithelial membranes and “beat” to create a current, moving particles

• Can be found in the fallopian tubes, trachea, and other organs

Central Dogma of Biology

1. DNA codes for RNA. These are the instructions for how to make a protein. RNA is made in the nucleus.

2. RNA leaves the nucleus and travels to the rough ER, where there is a large collection of ribosomes. It binds to a ribosome, where the protein is actually made

3. Once complete, the protein undergoes some changes in the ER, then it is sent to the Golgi apparatus.The Golgi packages the protein into a vesicle, which then leaves the cell.