Biosc 0150 Foundations of Biology I Review3 Chapter 7 1 Prokaryotic Structure Review Chapter 7 The cell a The shape of a prokaryote s chromosome is while the shape of eukaryotic chromosomes is Circular linear b Explain why it is necessary for the chromosome of a prokaryote to be highly coiled within the cell When stretched into linear form a prokaryote s chromosome can be up to 500 times the length of the cell itself Supercoiling of the chromosome with the aid of enzymes allows the chromosome to fit within the cell c What is a plasmid What purpose does a plasmid serve in a bacterial cell Are plasmids essential to bacterial survival A plasmid is a stretch of DNA that contains genes and is physically independent from the main chromosome does not carry essential functions to cell survival Plasmids serve as auxiliary genes and may contribute to adaptation to changed environmental conditions commonly carry resistance genes Plasmids are exchangeable between different bacterial cells and disseminate genes throughout and among bacterial populations Scientists often manipulate bacteria by injecting them with certain plasmids as you will learn in Biology 0060 d What is the purpose of a bacterial cell wall What is its main structural component Bacterial cell walls give added support to the cell Because the inside of a bacterial cell is usually hypertonic to its environment water enters the cell via osmosis through the plasma membrane The cell wall prevents the cell from bursting due to the influx of water The main component of bacterial cell wall is peptidoglycan 2 Explain how the pulse chase experiment is done It consists of two parts the pulse and then the chase For the pulse the cells to be experimented on are exposed to high concentrations of labeled molecules can be radioactive leucine for amine acids for a brief time Then large amounts of unlabeled versions of the same molecule are added for the chase The point of this is to have a molecule you can actually follow over time and see where it ends up a Why is it necessary to expose the experimental cells to a high concentration of labeled molecules for a short time If you were to use a lot of the labeling molecule it would be hard to tell where specific populations of labeled molecules were moving b Using the logic of a pulse chase experiment if you were to radioactively label proteins in the rough endoplasmic reticulum where might you find them after several minutes In the several minutes after labeling you might find the labeled proteins in the Golgi apparatus if it didn t travel far c Explain the path a protein takes when it goes through the endomembrane system from the start of its synthesis on the Rough ER to secretion Use the terms secretory vesicles plasma membrane Ribosome Rough ER and Golgi apparatus Ribosomes attached to the Rough ER produce protein strands that need to be processed in the Rough ER and eventually reach the Golgi apparatus where they are further processed and possibly labeled with carbohydrates so that when they reach the secretory vesicles they can be directed to the plasma membrane for secretion d You label a certain protein and preform a pulse chase experiment You waited 4 hours and went to check on the cell only to find that none of the proteins you labeled are present What might have happened You probably waited too long and after four hours the protein went through the Rough ER the Golgi apparatus and eventually was probably secreted out of the cell so you couldn t find the labeled protein in that cell Adel Anthony Kathleen Megan Dr Swigonova Page 1 of 8 Biosc 0150 Foundations of Biology I Review3 Chapter 7 3 True or false if the statement is false correct it If statement is correct support it with additional information a Cells perform specialized functions and have structures that suit their needs For example muscle cells are packed with mitochondria to produce ATP and specialized proteins that take part in muscle contraction The reason of cell functional and structural diversity is that they differ in their genomic DNA False An organism s DNA is the same throughout its entire body The difference between certain cell types arises when certain genes are selectively and differentially expressed b A fat cell would be expected to contain a large amount of smooth endoplasmic reticulum ER True SER is the site of fat metabolism c On the scale of a cell gravity has a small effect on movement of molecules False Gravity has no effect on the movement of molecules Electrostatic attractions dominate at the cellular and atomic level 4 Does the nucleus of a eukaryotic cell have a single or double membrane Double An opening into the cytosol from the nucleus is called a Nuclear pore The is selective for letting certain molecules enter the nucleus It is made up of a few 20 over 50 different proteins and forms an elaborate structure It allows certain molecules to enter the nucleus if they have the proper The rate at which molecules enter and leave the nucleus is Nuclear pore complex over 50 nuclear localization signal rapid Which of the following is most likely to enter the nucleus through a nuclear pore complex A DNA B small molecules C really large molecules that have nuclear localization signals D mRNA Answer C 5 Why is it that energy is required to move proteins through a cell while ions and amino acids do not Ions and amino acids are small molecules that can diffuse randomly throughout a cell however proteins are large molecules that are regulated in where they must go so energy is certainty required to move these bulky molecules to specific portions of the cell rather than having them move about randomly a What manufactures amino acids that are about 20 units longer than proteins that are synthesized in the rough ER Where would you find them These proteins are manufactured by isolated ribosomes and they are not located on the rough ER but can be found floating around in the cytosol b Why is the amino acid chain 20 units longer than a normal sequence made from the ribosomes on the rough ER The 20 extra amino acids are a send to ER signal which will eventually be removed once in the organelle c Explain the five step process of the Signal Hypothesis 1 A Ribosome synthesizes the ER signal sequence 2 The Signal sequence binds to a signal recognition particle 3 The ribosome signal sequence and SRP attaches to an SRP receptor in the ER membrane 4 Once the receptor and SRP connect the SRP is released 5 The signal sequence