Chapter 1:Principles of Life Unit 2: Cells, membranes and signaling

Biology—the scientific study of living things “ Living things”—All the diverse organisms descended from a single-celled ancestor (a single common ancestor) Characteristics shared by all living organisms: Composed of a common set of chemical components and similar structures – CELLS! Contain genetic information that uses a nearly universal code Convert molecules obtained from their environment into new biological molecules Extract energy from the environment and use it to do biological work Regulate their internal environment Replicate their genetic information in the same manner when reproducing Share sequence similarities among a fundamental set of genes Evolve through gradual changes in genetic information

Earth formed between 4.6 and 4.5 billion years ago. It was some 600 million years or more before the earliest life evolved.

Complex biological molecules Experiments that simulate conditions on early Earth show that this was possible. Critical step for evolution of life—formation of nucleic acids Biological molecules were enclosed in membranes, to form the first cells. Fatty acids were important in forming membranes.

For 2 billion years, organisms were unicellular prokaryotes. PRO means “before”. Prokaryotes are simple, with no nucleus or membrane-bound components. Early prokaryotes were confined to oceans, where they were protected from UV light. There was little or no O 2 in the atmosphere, and hence no protective ozone (O 3 ) layer.

Photosynthesis evolved about 2.7 billion years ago. The energy of sunlight is transformed into the energy of biological molecules. Earliest photosynthetic cells were probably similar to cyanobacteria. O 2 was a byproduct of photosynthesis, and it began to accumulate in the atmosphere and O 2 was poisonous to many early prokaryotes! Organisms that could tolerate O 2 evolved aerobic metabolism (energy production using O 2 ), which is more efficient than anaerobic metabolism. Organisms were able to grow larger (Aerobic metabolism is used by most living organisms today) O 2 also produced a layer of ozone (O 3 ) in the upper atmosphere. This layer absorbs UV light, and its formation allowed organisms to move from the ocean to land.

Some cells evolved membrane-enclosed compartments called organelles. Example: The nucleus contains the genetic information. These cells are eukaryotes. Prokaryotes lack nuclei and other internal compartments. Some organelles may have originated by endosymbiosis, when larger cells engulfed smaller ones. Mitochondria (site of energy generation) probably evolved from engulfed prokaryotic organisms. Chloroplasts (site of photosynthesis) probably evolved from photosynthetic prokaryotes. Some components of the cell are called: “SUB-CELLULAR COMPONENTS” because they aren’t actually organelles. Example: cell membrane, cytoskeleton, cytoplasm)

Biological systems are organized in a hierarchy. Traditionally, biologists concentrated on one level of the hierarchy, but today much biology involves integrating investigations across many levels. Multicellular organisms arose about 1 billion yrs ago. Cellular specialization: cells became specialized to perform certain functions.

Living organisms acquire nutrients from their environments. Nutrients supply energy and materials for biochemical reactions. Some reactions break nutrient molecules into smaller units, releasing energy for work (hydrolysis). Examples of cellular work : 1.Synthesis—building new complex molecules from smaller chemical units 2.Movement of molecules, or the whole organism 3.Electrical work of information processing in nervous systems 4.Metabolism is the sum total of all chemical transformations and other work done in all cells of an organism. (The reactions are integrally linked—the products of one are the raw materials of the next)

In multicellular organisms, cells are specialized, or differentiated. Differentiated cells are organized into tissues. Tissue types are organized into organs, and organ systems are groups of organs with interrelated functions. These organisms are HIGHLY SPECIALIZED

Categorize the examples on the board! Three domains of life: Bacteria (prokaryotes)- - E. coli - Streptococcus - Lactobacillus Archaea (prokaryotes)- - Methanobacterium - Thermophiles Eukarya (eukaryotes)- - Yeast- Amoeba - Muscle Tissue- Dinoflagellets NON-lIVING THINGS: Rhinovirus, HIV, Soil