Biology Study Guide 4

What are the three basic principles of the cell theory?

(1) Every organism is made up of one or more cells. (2) The smallest organisms are single cells, and cells are the functional units of multi-cellular organisms. (3) All cells arise from preexisting cells.

Name the proteins of the eukaryotic cytoskeleton; describe their relative sizes and major functions.

1) Microfilaments: smallest, twisted double strands, important in muscle contraction and cell division; 2) intermediate filaments: midsize, internal scaffolding, help maintain cell shape; 3) microtubules: largest, guide chromosomes during cell division, major component of cilia and flagella, transport organelles through the cytosol

Which cytoplasmic structures are common to both plant and animal cells, and which are found in one type but not the other?

Animal and plant cells share the following cytoplasmic structures: cytoskeleton, endoplasmic reticulum, Golgi apparatus, vesicles, vacuoles, mitochondria, and ribosomes. Lysosomes and centrioles are absent or rare in plant cells. Chloroplasts and the central vacuole are absent or rare in animal cells.

How are lysosomes formed? What is their function?

Lysosomes are membrane-enclosed vesicles derived from the Golgi complex that contain digestive enzymes that are used to break down food particles and defective organelles.

What are the functions of mitochondria and chloroplast? Why do scientists believe that these organelles arose from prokaryotic cells? What is this hypothesis called?

Mitochondria extract energy from food molecules and store it in the bonds of ATP; chloroplasts are the sites of photosynthesis. Their double membranes could have originated from their original host cell (outer membrane) and its prokaryotic guest (inner membrane). The organelles also have their own DNA, their own ribosomes, the ability to make ATP, and a size similar to that of prokaryotic cells, all supporting the endosymbiont hypothesis.

Diagram the structure of eukaryotic cilia and flagella. Describe how each moves and what their movement accomplishes.

Refer to Figure 4-8 for diagrams of cilia and flagella. Cilia (short and numerous) move in a way that resembles the oars of a rowboat. In multicellular organisms, cilia move fluid past a surface; in some protists they allow the cell to swim. Flagella (longer and fewer) propel sperm and some protists through fluid like a propeller on a motorboat.

What is the function of ribosomes? Wherein the seller they found? Are they limited to eukaryotic cells?

Ribosomes are sites for protein synthesis. They are embedded in the outer nuclear membrane of the nuclear envelope and the rough endoplasmic reticulum. They are also found free in the cytoplasm or attached to strands of mRNA as polyribosomes. Ribosomes are found in both eukaryotic and prokaryotic cells, although prokaryotic ribosomes are smaller and have different RNA and proteins.

List the structures of bacterial cells that have the same name and function as some eukaryotic structures, but a different molecular composition.

Ribosomes, cell wall, flagella

Describe the structure and function of the endoplasmic reticulum (smooth and rough) and the golgi apparatus and how they work together.

The endoplasmic reticulum forms membrane-enclosed channels in the cytoplasm. Smooth ER lacks ribosomes but contains enzymes. Some smooth ER enzymes synthesize steroid hormones; smooth ER in liver cells detoxifies drugs and metabolic wastes; muscle Smooth ER stores calcium ions. Rough ER is the major site of protein synthesis. Proteins synthesized by the ribosomes attached to the rough ER enter the channels of the endoplasmic reticulum, where they are chemically modified and folded and transported through the ER to pockets that pinch off as vesicles. Vesicles transport the proteins to the Golgi apparatus. The Golgi apparatus is a series of specialized flattened membranous sacs. The Golgi sorts, chemically alters, and packages proteins produced by the rough ER. These leave the Golgi in vesicles and are transported to other parts of the cell or to the plasma membrane for export.

Describe the nucleus and the function of each of its components, including the nuclear envelope, chromatin, chromosomes, DNA, and the nucleolus.

The nucleus houses the DNA in eukaryotic organisms. It is surrounded by the nuclear envelope, which consists of two membranes containing numerous pores that allow various molecules to pass between the nucleus and the cytoplasm. Chromatin consists of chromosomes in an uncondensed state. A chromosome is a DNA molecule with associated proteins. DNA carries genes whose nucleotide sequence codes for the production of proteins and RNA. The nucleolus, a dark-staining region of the nucleus, is the site of ribosome synthesis. It consists of rRNA, proteins, ribosomes in various stages of synthesis, and the portions of chromosomes carrying genes that code for rRNA.