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BIOLOGY 173 Final: Exam Study Guide at UMich

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azuremammoth471
8 Jan 2019
School
U of M
Department
Biology
Course
BIOLOGY 173
Professor
All

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Document Summary

Every cell in an organism has the same dna. Yet cells differ in their function and appearance. Control which genes are on/off in a cell. Constitutive expression: genes that are continuously expressed in all the cell types in an organism. Regulated expression: genes are not continuously expressed, expression is induced or repressed depending on environment. When lactose is not present, cell does not make beta-galactosidase. Take a lot of cells and add a mutagen to them, all the cells will have different mutations. However there will be a small group of cells that have been mutated so that they cannot utilize lactose as a carbon source. If there is a mutation here however, the repressor protein will never be able to bind here. Promoter and operator are too close for both laci and rna polymerase to bind simultaneously. In prokaryotes, transcriptional control is generally about controlling rna polymerase binding to the promoter.

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Related Questions

1. The lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. The operon system is inducible in that it can be ‘turned on’ by the presence of lactose. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products.

These mutations include:

I - = produces a repressor protein that can not bind to the operator region

I s = produces a repressor protein that can not be removed from the operator region

O C = can not bind a repressor protein

Z - = produces a defective (non-functioning) β-galactosidase enzyme

( I- are recessive to I+; I+ recessive to IS )

Detail the functionality of the lac

operon under the following genetic and cellular conditions.

GENES

Lactose

present

Repressed

(yes/no)

Constitutive

(yes/no)

Inducible

(yes/no)

I + O + Z +

no

I + O C Z +

no

I S O + Z +

yes

I - O + Z +

yes

I S O C Z +

no

Are my answers correct?

1. If a bacterium with a wildtype lac operon is grown in the presence of lactose, high levels of transcription result for a while, however, eventually transcription is again down-regulated. If, on the other hand, the sugar IPTG is present (instead of lactose), transcription levels are high and remain high. What function do IPTG and lactose share? How are they differently affected by the operon product?

Lactose and IPTG are both inducers of the Lac-Operon. Lactose is a substance that the enzyme will react with (substrate), which is split or cleaved by the Beta-galactosidase. When you add lactose expressions level of lac operon will increase but as lactose is used by the beta-galactosidase expression levels of lac operon will decrease.

IPTG is a chemical cannot be split or cleaved by beta-galactosidase. The expression level of lac operon will remain the same.

Or Lactose can be easily broken down but IPTG cannot be broken down. What does expressions level mean?

2. If a lacI - bacterium is grown in the presence of the sugar X-gal, a blue dye appears; however, the concentration of X-gal decreases over time. What has happened to the X-gal?


If a lacI - bacterium is grown in the presence of the sugar X-gal, the Lacl is mutant or the gene is damaged which alters the genetic message carried by that gene. The LacI gene produces the repressor protein which switches off the operon, but since it is damaged no repressor protein is produced and the operon is switched on. The Lacl is transcribed into beta-galactosidase (lactose) The enzyme beta-galactosidase (lactose) splits or separates the X-gal which will result in decreased concentration of X-gal with time.

3. If a wildtype bacterium is grown in the presence of the sugar X-gal, transcription of the polycistronic m-RNA does not occur. What is X-gal unable to do? Without adding lactose (or genetically modifying the bacteria), how could you fix this problem

X-gal cannot form lactose, the repressor remains off and beta-galactosidase is not formed. This can be fixed by adding IPTG which can switch on the operon

2. Explain the structural role of the four different categories of biomolecules within a cell.

3. Explain how water, a steroid hormone, and a monosaccharide are transported into a cell down their concentration gradient and explain why the different molecules are transported in different ways.

4. Explain which forms of transport require energy and why, and how ATP facilitates energy-dependent transport.

5. All of the different types of biomolecules can serve as energy sources. Explain which biomolecules are catabolized in which metabolic pathways.

6. Whether or not the cellular machinery is in place for particular catabolic reactions to go forward depends on which genes are being expressed. Explain the different points, in a eukaryotic cell, at which gene expression might be regulated, and how.

7. The primary tasks of any organism are survival and reproduction. Acquiring biomolecules and catabolizing them to generate energy is a major factor in survival. For reproduction to occur, DNA must first be replicated so that it can be passed on. Describe the process of DNA replication.

8. If you wanted to replicate DNA artificially in large quantities, how would you go about it?

9. Once DNA has been replicated, what is the sequence of events in the cell cycle and in cell division that produce the gametes for sexual reproduction? Where does this event fit, along with other cell cycles, in the life cycle of the organism?

10. A number of physical traits in humans are controlled by a simple dominant/recessive relationship between two alleles; here are some examples (dominant/recessive):

Widow’s peak/no widow’s peak

Free earlobes/attached earlobes

Cleft chin/no cleft chin

Dimples/no dimples

Freckles/no freckles

Naturally curly hair (really curly, not wavy)/straight hair

Make a pedigree of your immediate family indicating the possible genotype of each family member (for the six genes listed above) based on their phenotype. If you are adopted, indicate the possible genotypes and phenotypes of your parents. You may make this part up.