Chapter 3

What is a Cell

A cell is the basic structure of life. To view any cell you need a microscope. No cell can be created without coming from a pre-existing cell.

How Cells are Organized

Human cells have many parts, plasma membrane, nucleus, DNA, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, cytoskeleton, centrioles, centrosomes, cytoplasm, mitochondrion, polyribosomes, and riosomes just to name some of them!

Human Biology Power Point Presentation, Human Biology 156 by Larry M. Frolich, Phd.

The Plasma Membrane

The Plasma membrane is made up of lipids called phospholipids bilayer, which has many proteins studded throughout the membrane. These proteins allow and regulate different substances to pass through the membrane. This happens five different ways, through osmosis (diffusion), facilitated transport, active transport, endocytosis, and exocytosis. Only the last three require additional energy to make the transfer happen.

Human Biology Power Point Presentation, Human Biology 156 by Larry M. Frolich, Phd.

The Nucleus and Protein Production

The nucleus contains DNA, RNA, amino acids, chromatin, ribosomes, and ribosomal RNA (rRNA). The DNA is the map or blueprint of all the protein sequences needed for that specific organism. RNA is the helper to DNA allowing protein synthesis to occur based on the DNA map of genetic information. Amino acids are the building blocks of proteins. Chromatin is a grouping of threads comprised on DNA and proteins. Ribosomes are organelles where protein synthesis is carried out. Ribosomal RNA (rRNA) is created in the nucleus by using DNA as a template to create subunits of ribosomes.

The endomembrane system contains the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, and vesicles. The endoplasmic reticulum (er) contains two parts, rough er which is studded with ribosomes, and the smooth er. The rough er contributes to protein synthesis and then the proteins enter the er interior for further modification. The smooth er on the other hand synthesizes the phospholipids that appear in the cell membrane and other more specialized tasks depending on the cell. Overall the er helps with transportation of large molecules throughout the cell. The Golgi apparatus is involved in the processing, packaging, and secretion of modified proteins from the er. Lysosomes are the vehicle by which material is digested in the cell sometimes they will even digest parts of the cell itself. In white blood cells they will engulf disease-causing microbes.

The Cytoskeleton and Cell Movement

The cytoskeleton consists basically of three parts; microtubules, intermediate filaments and actin filaments. These help the cell not only maintain shape but also can assist organelles to move, especially in cell division, or can help the organelles remain in place.

Cilia and flagella, both contain microtubules, and can move the cell itself. A good example would be a sperm cell, the tail would be a flagella.

Mitochondria and Cellular Metabolism

Mitochondria are basically the engine of the cell. It is where cell respiration takes place, oxygen and glucose are used CO2 is expelled and ATP is formed. There are four ways to produce ATP; glycolysis, the citric acid cycle, the electron transport chain, and fermentation. All require oxygen except fermentation, and is also the most inefficient. All of the reactions need enzymes and/or co-enzymes to produce ATP.

Sources:

Human Biology 10^th Edition by Sylvia S. Mader

Human Biology Power Point Presentation, Human Biology 156 by Larry M. Frolich, Phd.