Reports: Cell and Membrane Essay

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Sofie Y.

Homework #1

Chapter 3

1. Endocytosis is a type of vesicular transport in a cell, meaning that materials move into the cell via small membranous sacs. There are three types of endocytosis and they are pinocytosis, which is "cell drinking", liquids are allowed in the cell and these particles are carried into the cell by pinosomes. The other type is phagocytosis, which means "cell eating" and they are received by phagosomes. The third type of endocytosis is receptor mediated endocytosis, these are protein-coated vesicles that work to bring into cell substances that are hydrophobic like lipids.

2. The ER is attached to the nuclear membrane and it's a membranous organelle that has intracellular membranes. The ER has to parts to it, the SER and the RER. The SER's role is to synthesize lipids and carbohydrate. This organelles is smooth. The other part of the ER is the RER which is rough because of the ribosomes that lie on top of it. In the RER proteins are modified and packaged to be taken to the Golgi apparatus. These proteins are packed in transport vesicles, which are small membranous sacs pinched off from the tips of cisternae.

3. Diffusion is a type of passive transport. It is the movement of chemical substances across the cell membrane. It does not require energy and its concentration gradient goes from high to low until it is evenly distributed. The four types of diffusion are simple diffusion, channel mediated diffusion, facilitated diffusion and osmosis. Simple diffusion diffuses dissolved gases (O2 and CO2), lipid soluble drugs, alcohol, fatty acids, and steroids can pass the lipid portion of the membrane freely. Channel mediated diffusion is through small channels made of proteins, water molecules exit freely and ions can enter and exit depending on charge, size of hydration sphere and interactions within channel wall. Facilitated diffusion or carrier mediated diffusion occurs when lipid- insoluble molecules are too large to fit through membrane channels and need help entering, involves a carrier molecule, but solute moves down its concentration gradient. The molecule binds to a receptor site which then causes a conformational change in the protein allowing the molecule to pass. Osmosis is a type of diffusion where only water substances can go pass the membrane, solutes are not allowed. Water moves through the selectively permeable membrane toward the solution that has a higher concentration. The rate of diffusion is affected by distance (shorter distance faster diffusion), molecular size (smaller the substance faster diffusion), temperature (higher temperature - faster diffusion), gradient change (higher the concentration the diffusion rate increases), and electrochemical forces ( positive and negative-repel).

4. Cancer cells are different than normal cells in shape, replication and in rate of production. Cancer is an illness due to mutations that disrupt normal control mechanisms and produce malignant cells. These mutations occur during cell differentiation, when a stem cell is used to produce specific types of cells and during the process this goes wrong. From cancer cells tumors are formed, which is an enlarged mass of these cells that start duplicating rapidly and take the place (invasion) of normal cells. These cancer cells are larger in size than normal cells and they also have an abnormal shape.

5. Within the nucleus of a cell is DNA, which contains our genetic make-up. In the DNA is where protein synthesis begins and it continues through other various organelles. A gene of the DNA contains specific sequences to code for a certain protein. To make a protein from the DNA a genetic code, or a sequence of three nucleotides is needed. When mRNA is ready to read the DNA for these genetic codes, the double-stranded DNA uncoils which makes the histones remove from holding the two strands together. Any weak bonds between the four nitrogenous bases are disrupted. The enzyme of RNA,
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