Chapter 6- A Tour of the Cell

Explain the functions of lysosomes in the cell. Where do lysosomal enzymes (hydrolysis) come from? What prevents the hydrolysis from breaking down the organelles that make them?

A membranous sac of hydrolytic enzymes that an animal cell uses to digest macromolecules. These enzymes work best in acidic env. found in lysosomes. If lysosome breaks open its contents aren't very active because cytosol has neutral pH. Excessive leakage from lysosome can destroy cell through autodigestion. They carry out intracellular digestion. Organisms that eat by engulfing smaller organisms through process called phocytosis.This forms food vacuole which fuses with lysosome whos enzyme ( hydrolase) digests the food through hydrolysis which breaks down. Digestion products pass into cytosol and become nutrients for cell. This is done by amoeba and immune cells ( macrophages ). Macrophages are a type of white blood cell that helps defend body by engulfing and destroying bacteria and other invaders. Hydrolytic enzymes also recycles cells own material, a process called authophogy. In this process, a damaged organelle or cytosol becomes surrounded by double membrane and lysosomes fuse with it. Lysosomal enzymes dismantle enclosed material and organic monomers are returned to cytosol for reuse. Lysosomes help the cell constantly renew itself. Made from Rough ER. They are probably synthesized by ribosomes, which then pass the enzymes through the ER and then Golgi. They are spared from destruction because they have 3d shapes that protect from vulnerable bonds from enzymatic attack.

What do ribosomes do in cells? What 2 types of macromolecules are ribosomes constructed from? What is the difference between free and bound ribosomes?

Carry out protein synthesis. They build protein in two cytoplasmic locales. Ribosomal RNA and protein/polypeptides Free ribosomes are suspended in the cytosol, while bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope. They are structurally identical. Most proteins made in the free ribosomes function within the cytosol, like enzymes that catalyze the first steps of sugar breakdown. Bound ribosomes make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or to export from cell like secretion.

Many cytoskeletal functions depend on motor proteins. What do they do? What energy drives them?

Cytoskeletal elements along with motor proteins work together with plasma membrane molecules to allow whole cells to move along fibers outside the cell. They bring about the bending of the cilia and flagella by gripping microtubules within those organelles and sliding them agains each other. A similar mechanism involving microfilaments causes muscle cells to contract.

List all organelles whose membranes are considered part of the endomembrane system. Why are the added surface area and compartmentalization useful?

Endoplasmic Reticulum Golgi Apparatus lysosomes food vacuoles plasma membrane

Where in a cell are the proteins made by free ribosomes found? where are proteins made by bound ribosomes found?

In the cytosol Membranes, for packaging within lysosome, or to export for cell secretion.

Describe the functions performed by the smooth ER

Involved in synthesis and transport of lipids. Detoxification of a variety of poisons. stores calcium ions. Stores glycogen.

What are the 3 general types of microscopes, and what is each type suited for?

Light Microscope- an optical instrument with lenses that refract (bend) visible light to magnify images of specimens Electron Microscope- electron microscope (EM) a microscope that uses magnets to focus an electron beam on or through a spectrum, resulting in a practical resolution of a hundredfold greater than that of a light microscope using standard techniques. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of the cell surface. Scanning electron microscope (SEM)- a microscope that uses an electron beam to scan the surface of the sample, coated with metal atoms, to study details of its topography. Transmission electron microscope (TEM)- a microscope that passes electron beam through very thin sections stained with metal atoms and is primarily used to study the internal ultrastructure of cells

Name the three types of cytoskeletal fibers and describe the structure and functions of each

Microtubules, microfilaments, and intermediate filaments. microtubules- Hollow tubes, walls consist of 13 columns of tubulin molecules. 25 nm. The wall of the tube is made of protein called tubulin. Each protein tubulin is a dimer, a molecule made up of two subunits. A tubulin dimer is made of two different polypeptides, alpha and beta tubulin. Microtubules grow in lenght by adding tubulin dimers. Because of its architecture, the two ends are slightly different. One end can accumulate or release tubulin dimers at higher rate than the other. Thus growing significantly during cellular activities. Shape and support cell and serve as tracks along which organelles equipped with motor proteins can move. Separate chromosomes during cell division.Know that they guide movement of vesicle. The vesicle travels along microtubule - they pull apart chromosomes in cell division - grow out of a central organelle and prior to cell division will have 2 centrosomes and during cell div. will shoot out microtubles. microfilaments- Two intertwined strands of actin ( a globular protein ) each a polymer of actin subunits. Main functions are maintenance of cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming, cell motility. cell division ( cleavage furrow formation ). 7nm. Animal cell division - pinches cell in two during animal cell division Dynamic function! - can break down and reconstruct into a ring shape and has capability of contract. The ring is made up of microfilaments. intermediate filaments-Fibrous proteins supercoiled into thicker cables. 8-12 nm. One of several different proteins of keratin family. Main functions are maintenance of cell shape, anchorage of nucleus and certain other organelles and formation of nuclear lamina. Gives shape/support to nucleus.Main structural component of hair/nails etc..

What is the structure and function of the nucleus? Name another organelle in animal cells, and 2 other organelles in plant cells where DNA is also found

Nucleus contains most of the genes in eukaryotic cell. Most conspicuous organelle in cell. Enclosed by nuclear envelope which separates its content from cytoplasm. Chromosomes found within Nucleus, they contain DNA. Contains nucleolus, which is a densely stained granule adjoining part of chromatin.Directs protein synthesis by synthesizing mRNA based on instructions of DNA. Animal cells - genes found in mitochondria and nucleus. Plant cells - Chloroplast, nucleus, mitochondria.

Why does the surface area to volume ratio place a limit on the size of the cells?

Only a limited amount of a particular substance can cross per second, so ratio is critical. As cell increases in size, its volume increases more than surface area. Thus, smaller object has greater surface area to volume

Which types of cells have cell walls? Which type has an extracellular matrix? What are these various structures made of? (It's different in each kingdom.) What functions do they serve?

Plant cells, prokaryotes, fungi and some other protists. Animal Cells. Cell wall - prevents cell from excessive water intake, gives support and form to multicellular organisms.

What makes prokaryotic and eukaryotic cells different from one another? What features do ALL cells have?

Prokaryotic cells- smaller, higher surface area to volume -Bacteria & Archea -lack organelles -lack nucleus -70s ribosomes -flagella -Cytoplasm bound by the plasma membrane Both contain DNA, Genetic code is nearly universal Both cells have cytosol All cells have membranes Chromosomes Ribosomes Eukaryotic cells- larger, lower surface area to volume -plants, animals, fungi, protists -contain organelles -have nucleus -80s ribosomes -flagella and cilia

Summarize the structure and function of the rough ER and the Golgi apparatus

Rough ER- Has ribosomes on the outer part of the membrane. Makes proteins that can stay in ER or leave and travel to other parts of the EMS. It is a membrane factory for the cell. Grows in place by adding membrane proteins and phospholipids to its own membrane. Makes its own membrane phospholipids. Found in Eukaryotic cell. Like highway. Transport vesicles bud off from region of RER called transitional ER and travel to Golgi Apparatus.Within ER you find chaperones ( proteins ) which are made by bound ribosomes. Golgi Apparatus- Center of Manufacturing, warehousing, sorting and shipping. Like Post office. Made of flattened membranous sacs-cisternae-looks like stack of pita bread. Membrane of each cisterna in a sack separates its internal space from cytosol. Unlike ER, these sacs not connected.The cis face receives vesicles containing ER products and trans face dispatches vesicles. Found in Eukaryotic cell. Products modified in transit from cis to trans. Also manufactures certain macromolecules on its own. Refines products in stages, golgi enzymes refines products in stages. Before dispatching products, it sorts products and targets them for certain parts of the cell. Molecular identification tags like phosphate groups are added to products act like zip codes.Golgi vesicles go to cell membrane for secretion or to lysosomes.

Describe the structures and functions of mitochondria and chloroplasts. How did they originate? What evidence supports the endosymbiont theory?

mitochondria- sites of cellular respiration, the metabolic process that generates ATP by extracting energy from sugars, and other fuels with the help of oxygen. Have two membranes separating their innermost space from the cytosol. Membrane made of phospholipid bilayer with a unique collection of embedded proteins. Outermembrane smooth but innermembrane is crowded, with infoldings called cristae. Inner membrane divides the mitochondrion into two internal compartments. First intermembrane space is narrow region between inner and outer membrane. Second compartment, the mitochondrial matrix, is enclosed by the inner membrane, contains many diff enzymes as well as mitochondrial DNA and ribosomes. Enzymes in matrix catalyze some steps of cellular respiration. Other proteins that function in respiration, including enzymes that make ATP, including enzyme that makes ATP, are built into inner membrane. Cristae give the inner mitochondrial membrane a large surface area, thus enhancing the productivity of cellular respiration. chloroplasts- Made by free ribosomes in cytosol and by ribosomes contained within these organelles themselves. Semiautonomous and reproduce within cell.Contain chlorophyll, along with enzymes and other molecules that function in photosynthetic production of sugar. Contents partitioned from cytosol by envelope consisting of two membranes separated by intermembrane space. Inside are thyllakoids, which are stacked, each stack called granum. Fluid outside of thyllakoids called stroma, which contains chloroplast DNA and ribosomes as well as many enzymes. Membranes of chloroplast divide the chloroplast into 3 compartments, intermembrane space, stroma, and thyllakoid space. Not part of EMS. Have own DNA and ribosomes. Originated from Endosymbiont Theory. Evidence like shape/size, double membrane, semi-atonymous are all examples.