Biology exam #2 cells and cellular function

What is diffusion and why does it occur?

Fundamentally all cells depend and rely on basic property of diffusion- natural tendency of molecules to spread out from an area of high concentration to low concentration. Heat energy of molecules drive diffusion. The ultimate goal is to reach equilibrium, where both sides have an equal concentration of the molecule.

nuclear membrane

nuclear membrane: the membrane that encloses the nucleus. This bilayer membrane is made of lipids, and encases the genetic material in eukaryotic cells. The nuclear membrane is made up of a double lipid bilayer. There are small holes in the nuclear membrane called nuclear pores, and these pores allow content to move in and out of the nucleus. They also connect the inner membrane with the outer membrane.

nucleolus

nucleolus: dense area of nuclues where assembled from special RNA proteins, rewrite ribosomal RNA (rRNA) and combine it with proteins.

nucleus

nucleus: largest, most visible strucutere, double-membrane structure (2 phospholipid bilayer portions- cytoplasm and nuclear side), contains DNA (genetic material for life).

Describe the structure and function of the following cell parts: plasma membrane

plasma membrane: encloses a single compartment, a microscopic membrane of lipids and proteins that forms the external boundary of the cytoplasm of a cell or encloses a vacuole, and that regulates the passage of molecules in and out of the cytoplasm.

Describe the differences and similarities between prokaryotic cells and eukaryotic cells.

prokaryotic cells: -don't have a nucleus or organelle -bacteria, archae -smaller in size, uni cellular eukaryotic cells: -have a nucleus and organelles -single-celled or multi-celled -humans, plants, fungi, insects -bigger in size -more DNA, more transciption, more translation, more proteins -true nucleus bound by a double membrane -amaebas, paramecium, yeast= uni-cellular organisms both: -composed of cell(s) -basic unit of life -cell surrounded by a cell membrane -contains DNA -reproduces -regulate transport across a cell membrane and requires chemical energy for some cellular processes -lipid bilayer which is an arrangement of phospholipids and proteins that act as a selective barrier between the internal and external environment

ribosomes

ribosomes: numerous organelles that their structure consists of 2 sub-units: large and small, which both consist of ribosomal RNA (rRNA), it's function is a site where amino acids are bound together to form polypeptides.

rough endoplasmic reticulum

rough endoplasmic reticulum: associated with nuclear membrane, have ribosomes attached to outer surface, manufactures proteins to be exported from the cell or for placement in cell's plasma membrane.

vacuoles

vacuoles: storage compartments, plant cells typically produce one large vesicle, animal cells typically produce numerous small vacuoles. Vacuoles are membrane-bound sacs within the cytoplasm of a cell. In mature plant cells, vacuoles tend to be very large and are extremely important in providing structural support, as well as serving functions such as storage, waste disposal, protection, and growth.

flagella

flagella: constructed with a pair of microtubules around two individual microtubules. A flagellum is a whip-like structure that allows a cell to move.

smooth endoplasmic reticulum

smooth endoplasmic reticulum: functions as a network of compartments and passageways for the synthesis and transport of various substances, lacks attached ribosomes, involved in synthesis of lipids, especially phospholipids, place where poisonous hydophobic molecules are detoxified, storage for calcium ions.

vesicles

vesicles: a vesicle is a small structure within a cell, or extracellular, consisting of fluid enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis) and transport of materials within the cytoplasm. Vesicles are involved in metabolism, transport, buoyancy control, and temporary storage of food and enzymes . They can also act as chemical reaction chambers.

Illustrate and explain what would happen to a plant and animal cell placed in a hypertonic, isotonic, and hypotonic solution. Explain how these changes are related to osmosis.

-Animal cell hypotonic solution: lysed, swell up, bloating Isotonic solution: normal Hypertonic solution: shriverled, crenate -Plant cell hypotonic solution: turgid (normal), stiff cell Isotonic cell: flaccid, soft cell wall (flexible), a little malleable Hypertonic solution: plasmolyzed

How do surface area to volume ratios place limits on the size of cells? Explain how cells were able to evolve larger sizes and still maintain favorable surface area to volume ratios.

1) A cell is a metabolic compartment where a multitude of chemical reactions occur. 2) The number of reactions increase as the volume of metabolic volume within a cell increases. (The larger the volume the larger the number of reactions). 3) All raw materials necessary for metabolism can enter the cell only through its cell membrane. 4) The greater the surface area the larger the amount of raw materials that can enter at only one time. 5) Each unit of volume requires a specific amount of surface area to supply its metabolism with raw materials. The amount of surface area available to each unit of volume varies with the size of a cell. 6) As a cell grows its SA/V decreases. 7) At some point in its growth, its SA/V becomes so small that its surface area is too small to supply its raw materials to its volume. At this point the cell cannot get larger. The evolution from prokaryotic ancestors had to solve the problem of increasing cell size while allowing for efficient diffusion of molecules throughout cytoplasm.

What are four functions of proteins embedded in cell membranes?

1) Transport 2) Enzymatic Activity: facilitate chemical reactions 3) Signal Transduction: cell communication, chemical signals and starting a response 4) Cell-to-cell recognition: uses specialized proteins called glycoproteins that have a carbohydrate chain attached to it. 5) Intercellular joinings: important for multicellular and colonial organisms. 6) Extracellular attachments: cells bind to extracellular proteins.

Describe the following active transport processes. What purposes does each of these processes serve for a cell?: ion pumps

An ion transporter (or ion pump) is a transmembrane protein that moves ions across a plasma membrane against their concentration gradient through active transport. An ion pump is a membrane protein that pumps ions into and out of the cell, creating a concentration gradient. The use of integral proteins to move ions across plasma membrane from a LOW concentration to a HIGH concentration.

Define and explain the process of osmosis.

Diffusion of water across a selectively permeable membrane from the region of lower concentration to the region of higher solute concentration until the solute concentration is equal on both sides. Causes fluid gain to the cell. Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves across a semipermeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.

endocytosis

Endocytosis: is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. The membrane folds over the substance and it becomes completely enclosed by the membrane. At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytosol. There are two main kinds of endocytosis: Phagocytosis, or cellular eating, occurs when the dissolved materials enter the cell. The plasma membrane engulfs the solid material, forming a phagocytic vesicle. Pinocytosis, or cellular drinking, occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell, as shown in Figure below. When the channel is closed, the liquid is encircled within a pinocytic vesicle.

exocytosis

Exocytosis: describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. Newly made membrane proteins and membrane lipids are moved on top the plasma membrane by exocytosis.

Describe both the external and internal structures of prokaryotic cells

Internal: -cytoplasm: mostly water with high concentration of solutes (nutrients, salts, proteins, and enzymes) -DNA: floats with cytoplasm, usually one large chromosome that is circular, compacted to form a nucleolid region, also referred to as plasmids -Ribosomes: units made of a combination of RNA + protein, assemble into amino acids into polypeptides using information from RNA External: -plasma membrane: encloses a single compartment, a microscopic membrane of lipids and proteins that forms the external boundary of the cytoplasm of a cell or encloses a vacuole, and that regulates the passage of molecules in and out of the cytoplasm. -cell wall: exterior to plasma membrane, use polypeptidoglycan (proteins and sugars), defines shape of cell, combination of amino acids and carbohydrates to prevent cell from lysing in hypotonic environment (a lot of water, low in solutes). -capsule: exterior to cell wall, additional protective layer, made from lipids and polysaccharides, used for adhesion (stick to surfaces, maintain place in environment and communication. -flagella: work like stiff, helix-shaped rods, rotate and spin around like a propeller, motor that pushes and motors them around in a fluid environment. -Fimbriae: short structures that are hair-like, projections that can propel cell cores.

electrogenic pumps

It is a transport protein that generates voltage across a membrane. The sodium-potassium pump appears to be the major electrogenic pump of animal cells. The main electrogenic pump of plants, fungi, and bacteria is a proton pump, which actively transports protons (hydrogen ions, H+) out of the cell. The pumping of H+ transfers positive charge from the cytoplasm to the extracellular solution. By generating voltage across membranes, electrogenic pumps help store energy that can be tapped for cellular work. One important use of proton gradients in the cell is for ATP synthesis during cellular respiration.

Explain the currently accepted hypothesis for the evolution of eukaryotic cells from prokaryotic ancestors. What is the endosymbiosis theory and how does it pertain to the evolution of eukaryotic cells? What evidence supports the endosymbiosis theory?

Living things have evolved into three large clusters of closely related organisms, called "domains": Archaea, Bacteria, and Eukaryota. Evidence supports the idea that eukaryotic cells are actually the descendents of separate prokaryotic cells that joined together in a symbiotic union. In fact, the mitochondrion itself seems to be the granddaughter of a free-living bacterium that was engulfed by another cell, perhaps as a meal, and ended up staying as a sort of permanent houseguest. The host cell profited from the chemical energy the mitochondrion produced, and the mitochondrion benefited from the protected, nutrient-rich environment surrounding it. This kind of "internal" symbiosis — one organism taking up permanent residence inside another and eventually evolving into a single lineage — is called endosymbiosis. Endosymbiotic theory, that attempts to explain the origins of eukaryotic cell organelles such as mitochondria in animals and fungi and chloroplasts in plants was greatly advanced by the seminal work of biologist Lynn Margulis in the 1960s. Evidence: Both mitochondria and chloroplasts have double phospholipid bilayers. This appears to have arisen by mitochondria and chloroplasts entering eukaryotic cells via endocytosis. Mitochondria and chloroplasts are similar in size to bacteria, 1 to 10 microns. Mitochondria and chloroplasts DNA, RNA, ribosomes, chlorophyll (for chloroplasts), and protein synthesis is similar to that for bacteria. This provided the first substantive evidence for the endosymbiotic hypothesis. It was also determined that mitochondria and chloroplasts divide independently of the cell they live in.

Why are cell membranes said to be selectively permeable? What substances pass easily across cell membranes and what substances need help from membrane components?

The cell membrane controls the movement of substances in and out of cells and organelles. In this way, it is selectively permeable to ions and organic molecules. The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion. the membrane is impermeable to large water-soluble molecules, including ions and most biological molecules. The selective permeability of a plasma membrane is due to its structure and shape.

Diagram the structure of a phospholipid molecule and explain how its properties allow phospholipids to spontaneously assemble into membranes.

These are created when two sheets of phospholipid molecules align. The hydrophilic head in each layer face a surrounding solution while the hydrophobic tails face one another inside the bilayer. The hydrophilic heads interact with water while the hydrophobic tails interact with each other.A phospholipid is an amphipathic molecule which means it has both a hydrophobic and a hydrophilic component. A single phospholipid molecule has a phosphate group on one end, called the "head," and two side-by-side chains of fatty acids that make up the lipid "tails.

cell wall

cell wall: The plant cell wall is composed of cellulose. Cellulose is a structural carbohydrate and is considered a complex sugar because it is used in both protection and structure. The plant cell wall consists of three layers. The cell wall gives the plant its actual shape. It acts as a gatekeeper, because it determines what can come in and out of the cell in order to keep the cell protected.

centrioles

centrioles: The main function of the centriole is to help with cell division in animal cells. The centrioles help in the formation of the spindle fibers that separate the chromosomes during cell division (mitosis) Without centriole's, the chromosomes would not be able to move.

chloroplasts

chloroplasts: responsible for preforming photosynthesis, consists of three membranes: thylakoid membrane, inner and outer membrane, The thylakoid membrane forms a network of flattened discs called thylakoids, which are frequently arranged in stacks called grana.

cilia

cilia: A ciliated cell usually has hundreds or thousands of cilia, which move in unison like little oars. Sometimes a cell will also use cilia to funnel food into an oral groove. Various species of paramecium employ cilia for both purposes.

cytoplasm

cytoplasm: mostly water with high concentration of solutes (nutrients, salts, proteins, and enzymes)

golgi complex (apparatus)

golgi apparatus: consists of series of flat, sac-like compartments called cisternae, have a "cis" face where new materials are received, have a "trans" face where substances are released, location where molecules made in the endoplasmic reticulum are chemically modified prior to secretion from cell, transport to and from Golgi Apparatus occurs with use of vesicles.

intermediate filaments

intermediate filaments: maintenance of cell shape, anchorage of nucleus and certain other organelles, formation of nuclear lamina. Intermediate filaments are cytoskeletal components found in the cells of vertebrate animal species, and perhaps also in other animals, fungi, plants, and unicellular organisms. They are composed of a family of related proteins sharing common structural and sequence features.

lysosomes

lysosomes: Lysosomes hold enzymes that were created by the cell. The purpose of the lysosome is to digest things. They might be used to digest food or break down the cell when it dies.

actin filaments (microfilaments)

microfilaments (actin filaments): maintenance of cell shape, changes in cell shaoem muscle contraction, cytoplasmic streaming, cell motility, cell division. Cellulose in plants, chitin in fungi, silia in diatoms.

microtubules

microtubules: maintenance of cell shape, cell motility (flagella, cilia), chromosome movements in cell division, organelle movements. control the beating of cilia and flagella, locomotor appendages.

mitochondria

mitochondria: sites of cellular respiration, a process that used energy to generate ATP, consists of two membranes: outer and inner.