Chapter 4

Living things fall into three groups

Archaea, Bacteria, and Eukarya

Chloroplasts

Only in plant cells. Like mitochondria, have own DNA and ribosomes. Organelles that capture the energy from sunlight and convert it into chemical energy in a process called photosynthesis

Phagocytosis

Section of the plasma membrane of the macrophage invaginates (folds in) and engulfs a pathogen. That section then pinches itself off from the plasma membrane and becomes a vesicle, which fuses with a lysosome. The lysosome's hydrolytic enzymes then destroy the pathogen

Endoplasmic Reticulum

Series of interconnected membranous tubules that collectively modify proteins and synthesize lipids. However, these two functions are performed in separate areas of the endoplasmic reticulum: the rough endoplasmic reticulum and the smooth endoplasmic reticulum, respectively.

Rough Endoplasmic Reticulum (RER)

System of internal membranes within the cytoplasm. Membranes are rough due to the presence of ribosomes. functions in transport of substances such as proteins within the cytoplasm. The RER also makes phospholipids for cell membranes.

Intercellular Junctions

Structures between cells that allow neighboring cells to form strong connections with each other, prevent passage of materials, or establish rapid communication between adjacent cells. The three types of intercellular contact in animal cells are: desmosomes, gap junctions, and tight junctions.Plasmodesmata are junctions between plant cells.

Unlike prokaryotes, eukaryotes have

a membrane-bound nucleus, numerous membrane-bound organelles—such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others, and several rod-shaped chromosomes

Endosymbiosis

A theorized process in which early eukaryotic cells were formed from simpler prokaryotes. Eukaryotes may have been a product of one cell engulfing another, one living within another, and evolving over time until the separate cells were no longer recognizable as such

Prokaryote

A unicellular organism that lacks a nucleus and membrane bound organelles

Unified Cell Theory

the biological concept that states that all organisms are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells

peptidoglycan

Cell wall of prokaryotes, but NOT ARCHAEA. Made of a sugar polymer and polypeptide.

Cyanobacteria

Photosynthetic, oxygen-producing bacteria (formerly known as blue-green algae). Unlike most prokaryotes, they have extensive, internal membrane-bound sacs called thylakoids. Chlorophyll is a component of these membranes, as are many of the proteins of the light reactions of photosynthesis. Cyanobacteria also have the peptidoglycan wall and lipopolysaccharide layer associated with bacteria.

What structures does a plant cell have that an animal cell does not have? What structures does an animal cell have that a plant cell does not have?

Plant cells have plasmodesmata, a cell wall, a large central vacuole, chloroplasts, and plastids. Animal cells have lysosomes and centrosomes.

Gap junctions

Points that provide cytoplasmic channels from one cell to another with special membrane proteins. Also called communicating junctions. Similar to plasmodesmata in plant cells in function but not structure.

All cells share

1) a plasma membrane, an outer covering that separates the cell's interior from its surrounding environment; 2) cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found; 3) DNA, the genetic material of the cell; and 4) ribosomes, particles that synthesize proteins. However, prokaryotes differ from eukaryotic cells in several ways.

Characteristics of Eukaryotes

1. Cells with nuclei surrounded by a nuclear envelope with nuclear pores. This is the single characteristic that is both necessary and sufficient to define an organism as a eukaryote. All extant eukaryotes have cells with nuclei. 2. Mitochondria. Some extant eukaryotes have very reduced remnants of mitochondria in their cells, whereas other members of their lineages have "typical" mitochondria. 3. A cytoskeleton containing the structural and motility components called actin microfilaments and microtubules. All extant eukaryotes have these cytoskeletal elements. 4. Flagella and cilia, organelles associated with cell motility. Some extant eukaryotes lack flagella and/or cilia, but they are descended from ancestors that possessed them. 5. Chromosomes, each consisting of a linear DNA molecule coiled around basic (alkaline) proteins called histones. The few eukaryotes with chromosomes lacking histones clearly evolved from ancestors that had them. 6. Mitosis, a process of nuclear division wherein replicated chromosomes are divided and separated using elements of the cytoskeleton. Mitosis is universally present in eukaryotes. 7. Sex, a process of genetic recombination unique to eukaryotes in which diploid nuclei at one stage of the life cycle undergo meiosis to yield haploid nuclei and subsequent karyogamy, a stage where two haploid nuclei fuse together to create a diploid zygote nucleus. 8. Some have cell walls. It might be reasonable to conclude that the last common ancestor could make cell walls during some stage of its life cycle. However, not enough is known about eukaryotes' cell walls and their development to know how much homology exists among them. Homology is the existence of shared ancestry between a pair of structures in different organisms (a similarity that stems from evolution). If the last common ancestor could make cell walls, it is clear that this ability must have been lost in many groups (most obviously animal cells).

Plastids

A group of membrane‐bound organelles commonly found in photosynthetic organisms and mainly responsible for the synthesis and storage of food. Found in photosynthetic Eukaryotes. Like Eurkaryotes, appear to have an endosymbiotic origin.

Cytoskeleton

A network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement. There are three types of fibers within the cytoskeleton: microfilaments, also known as actin filaments, intermediate filaments, and microtubules.

Centrosome

A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles.

Cellulose

A substance (made of sugars) that is common in the cell walls of many organisms

What evidence is there that mitochondria were incorporated into the ancestral eukaryotic cell before chloroplasts?

All eukaryotic cells have mitochondria, but not all eukaryotic cells have chloroplasts.

Smooth Endoplasmic Reticulum (SER)

An endomembrane system whose functions include synthesis of carbohydrates, lipids (including phospholipids), and steroid hormones; detoxification of medications and poisons; alcohol metabolism; and storage of calcium ions.

Mitochondria

An organelle found in large numbers in most Eukaryotic cells, in which the biochemical processes of respiration and energy production (ATP) occur.

Eukaryote

An organism whose cells contain a nucleus

Desmosomes

Anchoring junctions that prevent cells from being pulled apart

Why does the cis face of the Golgi not face the plasma membrane?

Because that face receives chemicals from the ER, which is toward the center of the cell.

Chromatin

Clusters of DNA, RNA, and proteins in the nucleus of a cell

Golgi Apparatus

Complex of vesicles and folded membranes within the cytoplasm of most eukaryotic cells, involved in secretion and intracellular transport. The GA has a receiving (cis) face near the endoplasmic reticulum and a releasing (trans) face on the side away from the ER, toward the cell membrane. Transport vesicles that form from the ER travel to the receiving face, fuse with it, and empty their contents into the lumen of the GA. Newly modified proteins and lipids are then tagged with small molecular groups so that they are routed to their proper destinations. Finally, modified & tagged proteins are packaged into vesicles that bud from the opposite face of the Golgi. Some of these vesicles, transport vesicles, deposit their contents into other parts of the cell where they will be used, others, secretory vesicles, fuse with the plasma membrane and release their contents outside the cell.

Nuclear envelope

Double-membrane structure that constitutes the outermost portion of the nucleus. Both the inner and outer membranes of the nuclear envelope are phospholipid bilayers. Punctuated with pores that control the passage of ions, molecules, and RNA between the nucleoplasm and the cytoplasm.

Ribosomes

Enzyme complexes that are responsible for protein synthesis and are composed of both proteins and RNA.

Describe the hypothesized steps in the origin of Eukaryotic cells

Eukaryotic cells arose through endosymbiotic events that gave rise to the energy-producing organelles within the eukaryotic cells such as mitochondria and chloroplasts. The nuclear genome of eukaryotes is related most closely to the Archaea, so it may have been an early archaean that engulfed a bacterial cell that evolved into a mitochondrion. Mitochondria appear to have originated from an alpha-proteobacterium, whereas chloroplasts originated as a cyanobacterium. There is also evidence of secondary endosymbiotic events. Other cell components may also have resulted from endosymbiotic events.

Microfilaments

Fine, threadlike proteins found in the cell's cytoskeleton

Microvilli

Fingerlike extensions of plasma membrane of apical epithelial cells, increase surface area, aid in absorbtion, exist on every moist epithelia, but most dense in small intestine and kidney

Nucleolus

Found inside the nucleus and produces ribosomes

Intermediate filaments

Intermediate diameter and have structural functions, such as maintaining the shape of the cell and anchoring organelles. Keratin, the compound that strengthens hair and nails, forms one type of intermediate filament.

Flagella and Cilia

Long, hair-like structures that extend from the plasma membrane and are used to move an entire cell.

tight junctions

Membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid

Summary Prokaryotes and Eukaryotes

Prokaryotes are predominantly single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles. Many also have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1-5.0 µm. Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. Eukaryotic cells tend to be 10 to 100 times the size of prokaryotic cells.

Vesicles

Small membrane sacs that specialize in moving products into, out of, and within a cell

Peroxisomes

Small, round organelles enclosed by single membranes. They carry out oxidation reactions that break down fatty acids and amino acids. They also detoxify many poisons that may enter the body.

Lysosomes

The cell's "garbage disposal." Digestive enzymes within the lysosomes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles. In single-celled eukaryotes, lysosomes are important for digestion of the food they ingest and the recycling of organelles. These enzymes are active at a much lower pH (more acidic) than those located in the cytoplasm.

Endomembrane system

The collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles, that work together to modify, package, and transport lipids and proteins. It includes the nuclear envelope, lysosomes (which only appear in animal cells), vesicles, the endoplasmic reticulum, and Golgi apparatus,

Cytoplasm

The part of the cell referred to as cytoplasm is slightly different in eukaryotes and prokaryotes. In eukaryotic cells, which have a nucleus, the cytoplasm is everything between the plasma membrane and the nuclear envelope. In prokaryotes, which lack a nucleus, cytoplasm simply means everything found inside the plasma membrane.

Cytosol

The soluble portion of the cytoplasm, which includes ions, small molecules, and macromolecules. In eukaryotes, the cytoplasm also includes membrane-bound organelles, which are suspended in the cytosol. The cytoskeleton, a network of fibers that supports the cell and gives it shape, is also part of the cytoplasm and helps to organize cellular components.

Extracellular Matrix

The substance in which animal tissue cells are embedded, consisting of glycoproteins and the protein collagen.

Microtubules

Thickest of the cytoskeletal fibers. These are hollow tubes that can dissolve and reform quickly. Microtubules guide organelle movement and are the structures that pull chromosomes to their poles during cell division. They are also the structural components of flagella and cilia

Central Vacuole

in a mature plant cell, a large membranous sac with diverse roles in growth, storage, and sequestration of toxic substances.