Unit 3 (Week 9 Gene Expression at a Molecular Level) Flashcards
Fun Fact: The degree of obesity is often similar between genetically identical twins who have been raised apart. Possible hypothesis for the answer as to why people gain weight based on genetic factors?
Some people have inherited “thrifty genes” as hand-me-downs from their ancestors, who periodically faced famines and food scarcity. Such thrifty genes would be advantageous in allowing people to store body fat more easily and to use food resources more efficiently when times are lean. The negative side is that when food is abundant, unwanted weight gain, and associated diseases such as diabetes and heart disease, can constitute a serious health problem.
What can we broadly define a gene as?
A unit of heredity.
What do geneticists view at different biological levels?
Gene function
What is gene function either at the level of traits or at the molecular level?
Gene expression
What is a gene that serves as a template to make an mRNA molecule that contains the information to specify a polypeptide with a particular amino acid sequence?
Protein-encoding gene. Most genes are protein-encoding genes.
What was used as a successful approach in answering “How do genes affect the composition and/or function of molecules found within living cells?”
The study of mutations which is a heritable change in the genetic material of an organism.
What is a common amino acid found in human diets where mutations along the metabolic pathway can cause phenylketonuria, tyrosinosis, and alkaptonuria?
Phenylalanine.
What disease would result if a person inherited two defective copies of the gene that encodes phenylalanine hydroxylase?
A person with two defective copies of phenylalanine hydroxylase would have phenylketonuria.
Who was the one responsible for focusing on the inherited disease alkaptonuria, in which the patient’s body accumulates abnormal levels of homogentisic acid (also called alkapton)?
Archibald Garrod
This compound, which is bluish black, results in discoloration of the skin and cartilage and causes the urine to appear black.
What does it mean when a disease follows a recessive pattern of inheritance?
If the disease is recessive, an individual with the disease has inherited the mutant (defective) gene that causes it from both parents.
If only one is inherited, that gene will be masked and the dominant gene will prevail.
What did Garrod (1908) describe as a genetic defect that produces an inability to metabolize a certain compound?
Inborn error of metabolism
An inborn error refers to a mutation in a gene that is inherited from one or both parents. At the turn of the last century, this was a particularly insightful idea because the structure and function of the genetic material were completely unknown.
What did American geneticists George Beadle and Edward Tatum, after being interested in Garrod’s work on gene and enzyme relationships, focus their studies on?
Neurospora crassa, a common bread mold
What did Beadle and Tatum hypothesize about genes carrying the information to make a specific enzyme?
They reasoned that a mutation, that is, a change in a gene, might cause a defect in an enzyme required for the synthesis of an essential molecule, such as an amino acid.
What are strains that are without a mutation?
Wild-type strains
What enzyme function was missing in group 2 mutants in this experiment? (See Beadle and Tatum’s photo experiment in folder)
The ability to convert ornithine into citrulline is missing.
What was the hypothesis that Beadle and Tatum made that was later changed but their work on the role of genes and metabolism earned them the Nobel prize?
One-gene/one-enzyme hypothesis
How was the one-gene/one-enzyme hypothesis modified later? (4)
- The information to make all proteins is contained within genes, and many proteins do not function as enzymes.
- Some proteins are composed of two or more different polypeptides. The term polypeptide refers to a linear sequence of amino acids; it denotes structure. Most genes carry the information to make a particular polypeptide. By comparison, the term protein denotes function. Some proteins are composed of one polypeptide. In such cases, a single gene does contain the information to make a single protein. In other cases, however, a functional protein is composed of two or more different polypeptides. An example is hemoglobin—the protein that carries oxygen in red blood cells—which is composed of two α-globin and two β-globin polypeptides. In the case of hemoglobin, the expression of two genes (that is, the α-globin and β-globin genes) is needed to produce a functional protein.
- Some mRNAs (messenger RNAs) are spliced in alternative ways so they produce two or more polypeptides. This allows a single gene to encode more than one polypeptide.
- A fourth modification to the one-gene/one-enzyme hypothesis is that some genes produce non-coding RNAs that do not specify the amino acid sequence of a polypeptide.
[Review] T/F All information to make proteins are contained within genes, and they function as enzymes.
False. Yes, all of the information to make a protein is contained in genes however, all proteins do not function as enzymes.
[Review] T/F All proteins contain more than one polypeptide.
False. Proteins can be one polypeptide or more than one polypeptide.
[Review] What does polypeptide denote? What does protein denote?
Polypeptide denotes structure while protein denotes function.
[Review] T/F A single gene can sometimes contain the information to make a protein.
True.
[Review] Since proteins can involve two or more polypeptides, what MAY be needed in order for the protein to be synthesized?
Two or more genes would needed to expression different polypeptides.
For example, hemoglobin, the protein that carries oxygen in red blood cells, is composed of two a-globin and two B-globin polypeptides. In the case of hemoglobin, the expression of two genes, that is a-globin and B-globin genes, are needed to produce a functional protein, hemoglobin.
[Review] How are single genes able to encode more than one polypeptide?
The mRNAs are spliced in alternative ways so they produce two or more different polypeptides.
[Review] The fourth modification to the one-gene/one-enzyme hypothesis indicates what about genes and RNA?
Some genes produce non-coding RNAs that do not specify the amino acid sequence of a polypeptide.