Cell Membrane
Describe the components of the Cell membranes
A phospholipid is a lipid made of glycerol, two fatty acid tails, and a phosphate-linked head group. Biological membranes usually involve two layers of phospholipids with their tails pointing inward, an arrangement called a phospholipid bilayer. Cholesterol, another lipid composed of four fused carbon rings, is found alongside phospholipids in the core of the membrane. Membrane proteins may extend partway into the plasma membrane, cross the membrane entirely, or be loosely attached to its inside or outside face. Carbohydrate groups are present only on the outer surface of the plasma membrane and are attached to proteins, forming glycoproteins, or lipids, forming glycolipids.
Describe the composition and location of cells walls of prokaryotes and fungi.
A wall located outside the cell membrane provides the cell support, and protection against mechanical stress or damage from osmotic rupture and lysis. The major component of the bacterial cell wall is peptidoglycan or murein. This rigid structure of peptidoglycan, specific only to prokaryotes, gives the cell shape and surrounds the cytoplasmic membrane.
Explain the physical considerations that determine the upper and lower limits to cell size.
Cells cannot expand to much because then they will be unable to sustain their large size. Diffusion of oxygen will be inefficient and the cell will need too many nutrients. It will no longer be able to feed itself. However, if a cell is too small, then there will not be enough space for the organelles necessary for cells to carry out their functions.
Explain the relationship between active transport, free energy and proteins embedded in the membrane.
Free energy refers to energy in ATP form; it's no longer called potential energy because it's no longer stored in food molecules (an unusable form). Active transport requires ATP (free energy) because it's moving molecules against the concentration gradient. The exact structure of the carrier protein used to transfer the molecules depends on what molecule we're talking about, but the basic form is that molecules bind to the carrier protein and then the ATP follows. It breaks its bond with the third phosphate (which remains bound to the carrier protein), releasing energy and an ADP, and the energy changes the conformation of the protein so it opens on the other side of the membrane and releases the molecules
What properties do Phospholipids give the membrane?
Hydrophilic molecules are attracted to water, but hydrophobic are not. In water, phospholipids have a double layer with the hydrophilic heads facing the water and the hydrophobic tails are facing inward, away from the water. The attraction between the hydrophobic tails and the hydrophilic heads and the surrounding water makes membranes stable
Describe passive transport and explain its role in cellular systems
Passive transport is when molecules are able to pass through the cell membrane without requiring energy in the form of ATP. The cell membrane itself is selectively permeable, meaning only certain substances are allowed into the cell. For example, nonpolar hydrophobic molecules do not have to enter the cell through a transport protein.
How is selective permeability related to the fluid mosaic model.
Selective permeability allows cell to control which molecules to move in or out of cell. It is related to the fluid mosaic model because it is similar, both has cell membranes. Fluid mosaic model shows the arrangement of substances of cell membrane.
Describe the movement of the following through the membrane: Small, uncharged polar molecules, small nonpolar molecules (e.g. N2), Hydrophilic substances (e.g. large polar molecules and ions), and water.
Small, uncharged polar molecules and small nonpolar molecules, such as N2, freely pass across the membrane. Hydrophilic substances such as large polar molecules and ions move across the membrane through embedded channel and transport proteins. Water moves across membranes and through channel proteins called aquaporins.
Explain why smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.
Smaller cells have the more favorable ratio because they have the greater amount of volume for the least amount of surface area. Their smaller size allows cells to be more efficient in diffusion, since oxygen and carbon dioxide do not have to diffuse so much. We can also gets nutrients in more easily and waste products out.
Describe the function of the cell walls.
The cell wall is the protective, semi-permeable outer layer of a plant cell. A major function of the cell wall is to give the cell strength and structure, and to filter molecules that pass in and out of the cell.
Describe the orientation of phospholipids in a cell membrane.
The polar heads face outwards and the non polar tails face inwards of the cell.
Compare the strategies employed by different lineages of cells to acquire and utilize free energy.
Biological systems utilize free energy and molecular building blocks to grow, reproduce, and maintain dynamic homeostasis. Organisms have evolved various strategies to capture, use, and store free energy and other vital resources; for example, autotrophic cells capture free energy through photosynthesis and chemosynthesis, whereas fermentation and cellular respiration harvest free energy from sugars to produce free energy carriers, such as ATP, that drive metabolic pathways in cells.
Explain how membrane proteins play a role in facilitated diffusion of charged and polar molecules in general and in relation to the specific molecules below. ○ Glucose transport ○ Na+/K+ transport
Charged/polar molecules: Facilitated diffusion uses membrane proteins such as channel proteins and carrier proteins. Channel proteins can have ion channels and gated channels, which is a stimulus that causes the them to open or close. The charged/polar molecules simply flow down this channel. As for carrier proteins, the solute binds to the protein and the carrier protein changes shape to release the molecule on the other side of the membrane. Glucose transport: Glucose is transported across the membrane via a carrier protein, specific to the transport of glucose. Glucose molecules binds to the carrier protein, which causes the protein to change shape slightly and be released on the other side.
Describe the processes of endocytosis and exocytosis.
During endocytosis, the cell takes in macromolecules and particulate matter by forming new vesicles from the plasma membrane. A small area of the plasma membrane sinks inward to form a pocket, and as it deepens, it pinches in, forming a vesicle containing material that had been outside the cell. There are three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis.--- In exocytosis, materials are exported out of the cell via secretory vesicles. In this process, the Golgi complex packages macromolecules into transport vesicles that travel to and fuse with the plasma membrane. This fusion causes the vesicle to spill its contents out of the cell.
Explain the terms: hypotonic, hypertonic or isotonic in relationship to the internal environments of cells.
Hypotonic:in which the concentration of solutes is greater inside the cell than outside of it and water goes inside the cell. Hypertonic: when the concentration of solutes is less inside the cell than outside and water goes out of the cell. Isotonic: Equal concentration of solutes is the same inside and out and water moves equally.
Describe the chemical characteristics of membrane proteins, and how this effects their position in the membrane.
Integral proteins have hydrophilic regions at the top and bottom of the protein and and a hydrophobic region in the middle. As a result, the integral proteins are embedded in the membrane with the hydrophilic head faces outward and the hydrophobic region is placed between the phospholipids, aligned with the hydrophilic tails. Peripheral proteins don't have a hydrophobic or a hydrophilic region, so they're not embedded in the lipid bilayer.
Explain how internal membranes facilitate simultaneous occurrence of diverse cellular processes.
Internal membranes are used to separate the organelles inside the cell, in order to reduce unnecessary interactions. By doing so, they are able to increase surface area for the processes to occur. This allows cells to compartmentalize and have multiple functions occurring at once.
Describe active transport.
Movement of materials against the concentration gradient. Uses ATP. Endocytosis and Exocytosis
Describe the composition and location of plant cell walls.
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.
Explain why surface area-to-volume ratios are important in affecting a biological system's ability to obtain necessary resources or eliminate waste products.
The surface area-to-volume decreases as a cell gets bigger. If a cell were to lose surface area, its need for nutrients would actually increase. This increase in nutrient demand would then lead to a demand for more cell surface area in order for an increased amount of nutrients exchanged to occur. This is what maintains the surface area-to-volume ratios.The cell membrane must be large enough to allow the necessary resources to pass through the membrane and wastes to exit. But also, the cell cannot be small enough that it does not allow for space of the necessary organelles for cellular functions.
