AP Bio --> A Tour of the Cell

Explain why there are both upper and lower limits to cell size.

As an object of a particular shape increases in size, its volume grows proportionately more than its surface area. For each square micrometer of membrane, only so much of a particular substance can cross per second. Rates of chemical exchange with the extracellular environment will be inadequate to maintain a cell with a very large cytoplasm. The need for a surface sufficiently large to accommodate the volume helps explain the microscopic size of most cells. Larger organisms do not generally have larger cells than smaller organisms -- simply more cells.

Explain the advantages of compartmentalization in eukaryotic cells.

Because the cell's compartments provide different local environments that facilitate specific metabolic functions, incompatible processes can go on simultaneously inside the same cell.

Describe the major steps of cell fractionation and explain why it is a useful technique.

Cell fractionation -> The disruption of a cell and separation of its organelles by centrifugation. Fractionation begins with homogenization, the disruption of cells the objective is to break the cells apart without damaging their organelles. Spinning the soupy homogenate in a centrifuge separates the parts of the cell into two fractions: the pellet, and the supernatant. The supernatant is decanted into another tube and centrifuged again. The process is repeated until small enough pieces are obtained.

List the components of the endomembrane system and describe the structure and functions of each component.

Endoplasmic reticulum (Smooth ER, Rough ER,) Lysosomes, Vacuoles, Plasma membrane, Golgi apparatus. Transport vesicle, Nuclear envelope.

Describe the structure and function of a eukaryotic cell.

Eukaryotic cells are generally much larger than prokaryotes. They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. In addition to asexual cell division (mitosis), most eukaryotes have some process of sexual reproduction via cell fusion (meiosis), which is not found among prokaryotes.

Name three different kinds of vacuoles, giving the function of each kind.

Food vacuole -> A membranous sac formed by phagocytosis. Contractile vacuole -> A membranous sac that help move excess water from the cell. Central Vacuole -> A membranous sac in a mature plant with diverse roles in reproduction, growth and development.

Distinguish between free and bound ribosomes in terms of location and function.

Free ribosomes are suspended in the cytosol, while bound ribosomes are attached to the outside of the endoplasmic reticulum. Most of the protein made by free ribosomes will function within the cytosol; examples are enzymes that catalyze the first steps of sugar breakdown. Bound ribosomes generally make protein that are destined either for insertion into membranes, for packaging within certain organelles such as lysosomes, or for export from the cell (secretion.)

Describe the structure and function of the Golgi apparatus.

Golgi apparatus ->An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store and route products of the ER. After leaving the ER, many transport vesicles travel to the Golgi apparatus. The Golgi is a center of manufacturing, warehousing, sorting, and shipping. Here, products of the ER are modified and stored and then sent to other destinations. The Golgi is especially extensive in cells specialized for secretion. The Golgi has a distinct polarity, with cisternae at opposite ends of the stacks differing in thickness and molecular composition. Molecular identification tags, such as phosphate groups, aid in sorting. Cis face -> Receives material Trans face -> Sends material

Explain how the nucleolus controls protein synthesis.

In the nucleolus, rRNA is synthesized and assembled with protein imported from the cytoplasm into the main components of ribosomes (ribosomal subunits) These subunits then pass though the nuclear pores to the cytoplasm.

Describe the principles, advantages, and limitations of the light microscope, transmission electron microscope, and scanning electron microscope.

LIGHT MICROSCOPE Principals -> Visible light is passed though the specimen and then through glass lenses. The lenses refract the light in such a way that the image of the specimen is magnified as it is projected. Advantages -> Organisms survive. Limitations -> Limited resolving power. SCANNING/TRANSMISSION ELECTRON MICROSCOPE Principals -> Focuses a beam of electron through the specimen or onto its surface. Advantages -> Higher resolving power because electrons have shorter wavelengths than light. Limitations -> All organisms die.

Distinguish between magnification and resolving power.

Magnification -> The ratio of an object's image to it's real size. Resolving power -> A measure of the clarity of the image

Describe the basic structure of a plant cell wall.

Middle lamella -> This is the first layer formed during cell division. It makes up the outer wall of the cell and is shared by adjacent cells. It is composed of pectic compounds and protein. Primary wall -> This is formed after the middle lamella and consists of a rigid skeleton of cellulose microfibrils embedded in a gel-like matrix composed of pectic compounds, hemicellulose, and glycoproteins. Secondary wall -> formed after cell enlargement is completed. The secondary wall is extremely rigid and provides compression strength. It is made of cellulose, hemicellulose and lignin. The secondary wall is often layered.

Describe the evidence that mitochondria and chloroplasts are semiautonomous organelles

Mitochondria and chloroplasts have little bits of their own DNA. They also grow and reproduce within the cell.

Describe the structure and function of the nuclear envelope, including the role of the pore complex.

Nuclear envelope -> Double membrane enclosing the nucleus, perforated by pores. The nuclear envelope is a double membrane. The envelope is perforated by pores that are about 100 nm apart. At the lip of each pore, the inner and outer membrane of the nuclear envelope are fused. The nuclear envelope encloses the nucleus separating its contents from the cytoplasm.

Explain the role of peroxisomes in eukaryotic cells.

Peroxisome -> A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide. In eukaryotic cells, peroxisomes contain enzymes that transfer hydrogen from various substrates to oxygen, producing H2O2.

Describe three examples of intracellular digestion by lysosomes.

Phagocytosis -> (Cell eating) Digestion products, including simple sugars, amino acids, and other monomers, pass into the cytosol and become nutrients for the cell. Autophagy -> A process by which lysosomes are able to use their hydrolytic enzymes to recycle the cell's own organic material. Endocytosis -> Receptor proteins are recycled from the cell's surface.

Distinguish between prokaryotic and eukaryotic cells.

Prokaryotic cells -> A type of cell lacking a membrane bound nucleus and membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea. Eukaryotic cells -> A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, present in protists, plants, fungi, and animals <- eukaryotes

Compare the structure and functions of smooth and rough ER.

Smooth ER -> Functions in diverse metabolic processes, including synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons. Among the steroids produced by the smooth ER in animal cells are the sex hormones of vertebrates and various steroid hormones secreted by the adrenal glands. Rough ER ->Many types of cells secrete proteins produced by ribosomes attached to rough ER. Most secretory protein and glycoproteins, proteins that are covalently bonded to carbohydrates. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called transitional ER

Explain how the extracellular matrix may act to integrate changes inside and outside the cell.

Some cells in a developing embryo migrate along specific pathways by matching the orientation of their microfilaments to the "grain" of fibers in the ECM.

Describe the structure of a mitochondrion and explain the importance of compartmentalization in mitochondrial function.

The cristae give the inner mitochondrial membrane a large surface area that enhances the productivity of cellular respiration.

Describe the functions of the cytoskeleton.

The cytoskeleton helps to maintain cell shape. But the primary importance of the cytoskeleton is in cell motility. The internal movement of cell organelles, as well as cell locomotion and muscle fiber contraction could not take place without the cytoskeleton. The cytoskeleton is an organized network of three primary protein filaments: microtubules, actin filaments, and intermediate fibers.

Describe the structure and list four functions of the extracellular matrix.

The main ingredients of the ECM are glycoproteins. The most abundant of these glycoproteins is collagen, which forms strong fibers outside of cells. The collagen fibers are woven in a network of proteoglycans. Communicating with a cell though integrins, the ECM can regulate a cell's behavior. The ECM around a cell can also influence the activity of genes in the nucleus. The extracellular matrix of oa particular tissue could help coordinate the behavior of all the cells within that tissue

Briefly explain how the nucleus controls protein synthesis in the cytoplasm.

The nucleus directs protein synthesis by synthesizing mRNA and sending it to the cytoplasm via the nuclear pores. The mRNA is made according to instructions provided by the DNA, Once and mRNA molecule reaches the cytoplasm, ribosomes translate its genetic message into the primary structure of a specific polypeptide.

Identify the three functional compartments of a chloroplast. Explain the importance of compartmentalization in chloroplast function.

Thylakoids -> A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy. Granum -> A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis. Stroma -> The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide.

Briefly describe the energy conversions carried out by mitochondria and chloroplasts.

They convert solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water.

Name the intercellular junctions found in plain and animal cells and list the function of each type of junction.

Tight junctions -> bind cells together in such a way that no material can pass through the intercellular spaces. Epithelial cells are held together by tight junctions. Desmosomes -> These bind the cells together like rivets. They let material pass through the intracellular spaces. Gap Junctions -> They connect cells but allow material to pass from one cell to another through the opening in the center of the joint. They are analogous to the plasmodesmata in plants.