I hope everyone is having a great evening, 2 more days of school until the weekend! :)
Don't forget that test corrections are due on THURSDAY and ch 26 & 27 take home is due TOMORROW. Here are today's notes:
Chapter 27: Prokaryotes
Section 27.1: Structural, functional, and genetic adaptions contribute to prokaryotic success
Almost all prokaryotic cells have a cell wall. This wall helps maintain their shape, provides protection, and prevents the cell from bursting in a hypotonic environment.
Cell Surface Structures
The most common shapes are rods, spheres, and helices. Most are approx. 1-5 micrometers in length. This is perhaps 1/10 the size of a typical eukaryotic cell. Most cell walls of bacteria contain peptidoglycan (modified sugar polymers linked by short peptides). To distinguish the different types of bacteria, scientists use a process called gram staining. In this process, the bacteria are stained through a series of steps including the addition of crystal violet, an alcohol, and a mordant. The result is that the gram-positive bacteria are darker purple and the gram-negative bacteria are lighter. gram-positive bacteria have simpler cell walls so they contain more peptidoglycan which alludes to a darker purple color. The gram-negative bacteria have a more complicated cell wall so they contain less peptiglycan and are lighter in color.
The Cell wall of many prokaryotes also is covered by a capsule (a sticky layer of protein or polysaccharide). This capsule allows the cell to adhere to other individuals or their substrate. Other cells stick to their substrate or one another by appendages called fimbriae and pili. (Fimbriae are more numerous and shorter than pili).
Prokaryotic cells are able to move because of flagella. Many of these prokaryotes exhibit taxis or the movement away from or towards a stimulus like nutrients or oxygen. An example of these prokaryotes is E. Coli which exhibits taxis toward other individuals of its species leading to the formation of colonies.
Internal and Genomic Organization
Prokaryotes do not have a true nuclei nor do they have internal-compartmentalization. Prokaryotes' single chromosome is located in a nucleoid region. In addition to having one chromosome, a prokaryote may also contain rings of DNA called plasmids. These plasmids provide resistance against atibiotics and direct the metabolism of rare nutrients.
Reproduction and Adaption
Prokaryotic cells do not reproduce sexually. Instead they reproduce asexually through binary fission. Although meiosis and fertililzation does not occur in prokaryotes, genetic diveristy occurs through three different processes: transformation, transduction, and conjugation.
transduction: viral phages carry bacterial genes from one host cell to another
transformation: the alteration of a bacteria's cells genotype by the uptake of foreign DNA from the surrounding environment
conjugation: the direct transfer of genetic material between two bacterial phages that are temporarily joined
These organisms are able to adapt to their environments quickly and reproduce often so populations are constantly growing and evolving. Some prokaryotes have the ability to live in harsh conditions such as very salty water and in extreme temperatures. Certain bacteria can even form resistant cells called endospores (a thick-coated, resistant cell produced within a bacterial cell exposed to harsh conditions.
Section 27.2: A great diversity of nutritional and metabolic adaptions have evolved in prokaryotes
All organisms can be categorized by how they obtain energy and carbon used in building molecules that make up cells. Prokaryotes can be placed into four groups:
1. photoautotrophs- photosynthetic organisms that use light energy to produce their food and synthesize organic compounds from CO2. Examples include plants and algae.
2. chemoautotrophs- oxidize inorganic substances such as hydrogen sulfide, ammonia, and ferrous ions for energy. They also need CO2 as a carbon source.
3. photoheterotrophs-use light for energy but obtain their carbon in organic form. Examples include many marine prokaryotes.
4. chemoheterotrophs- consume organic molecules for both energy and carbon. Most commonly found among prokaryotes as well as protists, fungi, and even some plants
Metabolic Relationships to Oxygen
obligate aerobes- use 02 for cell respiration and can't grow without it
facultative anaerobes- use 02 if present but Can also grow by fermentation
obligate anaerobes- poisoned by 02, live only by fermentation
anaerobic respiration- the process in which chemical energy is extracted from substances other than 02 like nitrate ions or sulfate ions. They also accept electrons at the end of electron transport chains.
Match the term with the right definition
1) obligate aerobes a. live only by fermentation and are poisoned by O2
2) obligate anaerobes b. viral phages carry bacterial genes from one host cell to another
3) transformation c. oxidize inorganic substances such as hydrogen sulfide for energy
4) facilitative anaerobes d. use o2 for cell respiration
5) chemoautotrophs e. use light energy to make food and synthesize organic molecules from CO2
6) conjugation f. the direct transfer of genetic material between bacterial phages temp. joined
7) transduction g. the alteration of a cell's genotype by the uptake of foreign DNA
ANSWERS: 1. D 2. A 3. G 4. C 5. F 6.B