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.
What do you call the process that produces an RNA copy of a gene, which is also called an RNA transcript?
Transcription - The process that produces an RNA copy of a gene.
Transcription literally means the act of making a copy.
What is an RNA molecule that contains the information to specify a polypeptide with a particular amino acid sequence?
messenger RNA (mRNA)
Where does the functional mRNA carry the information it obtained from DNA?
To ribosomes.
What is the process of synthesizing a specific polypeptide on a ribosome?
Translation. The second step after transcription.
Where does transcription and translation happen in bacteria?
Cytoplasm
Where does transcription and translation happen within eukaryotic cells?
Transcription happens in the nucleus while translation happens in the cytosol. Ribosomes are located in the cytosol.
Why do we use the term “translation” in gene expression?
This is used because a base sequence in an mRNA is “translated” into an amino acid sequence of a polypeptide.
Who coined the term of central dogma which refers to the steps of gene expression at the molecular level: DNA is transcribed into mRNA, and mRNA is translated into a polypeptide?
Ya boy Francis Crick in 1958. This applies to archaea, bacteria, and eukaryotes.
What step happens between transcription and translation in eukaryotes?
RNA modification, which is the the biochemical modification of an RNA, which deals with the RNA transcript also known as pre-mRNA in the cell’s nucleus.
What is the direction of flow of genetic information?
The usual direction of flow of genetic information is from DNA to RNA to protein, though exceptions occur.
When does the direction flow from DNA to RNA to protein include exceptions?
Certain viruses use RNA as a template to synthesize DNA.
What provides a blueprint for the characteristics of every organism?
Genes that constitute the genetic material. They contain the information necessary to produce an organism and allow it to interact appropriately with its environment.
[Start Transcription] What must happen for genes to be expressed?
The information in them must be accessed at the molecular level.
Instead of accessing DNA directly, what is done to get the information?
A working copy of the DNA, composed of RNA, is made.
This occurs by the process of transcription, in which a DNA sequence is copied into an RNA sequence.
What is defined as at the molecular level, a _____ is defined as an organized unit of base sequences that enables a segment of DNA to be transcribed into RNA and ultimately results in the formation of a functional product?
A gene
Since most genes are protein-encoding genes, what may be the functional product itself which is transcribed but never translated?
The functional product will be RNA and one such molecule is called a non-coding RNA.
What are some examples of non-coding RNA?
Transfer RNA (tRNA) - An RNA that carries amino acids and is used to translate mRNA into polypeptides.
Ribosomal RNA - An RNA that forms part of ribosomes, which provide the site where translation occurs.
What is the sequence of DNA that controls when and where transcription will begin?
The promoter sequence.
What specifies the end of transcription?
The terminator.
What regulates transcription for the binding of regulatory proteins and affects the rate of transcription? It can either be enhanced or inhibited.
Regulatory sequences
What are the three stages of transcription where various proteins interact with DNA sequences?
Initiation, elongation, and termination.
What are similarities and differences between the function of DNA polymerase and that of RNA polymerase?
Both DNA and RNA polymerase use a DNA strand as a template and connect nucleotides to each other in a 5′ to 3′ direction based on the complementarity of base pairing. One difference is that DNA polymerase needs a pre-existing strand, such as a RNA primer, to begin DNA replication, whereas RNA polymerase can begin the synthesis of RNA on a bare template strand. Another key difference is that DNA polymerase connects deoxyribonucleotides, whereas RNA polymerase connects ribonucleotides.
What are the steps of initiation in transcription?
- Sigma factor binds to RNA polymerase.
- Sigma factor then recognizes the base sequence of a promoter and binds there.
- Sigma factor, therewithin, allows RNA polymerase to bind to the promoter as well.
- Initiation phase is complete when the DNA strands are separated near the promoter to form an open complex that is approx 10-15 bp long.
[Review] What is a protein that recognizes the promoter in a bacterial gene and binds RNA polymerase to the promoter as well?
Sigma factor
[Review] What is the enzyme that synthesizes strands of RNA during gene transcription?
RNA polymerase
[Review] When is the initiation phase completed?
When the DNA strands separate near the promotor.
[Review] What is formed when the DNA separates and the initiation phase is complete? How many bp long is it?
The open complex and it is approximately 10-15 base pairs long.
What is the second stage of transcription or translation, where RNA strands or polypeptides are made, respectively?
Elongation
What is synthesized during elongation after sigma factor is released and RNA polymerase begins to slide along the DNA that maintains an open complex as it goes?
RNA transcript
What is the DNA strand that is used as a template for RNA synthesis or DNA replication?
Template strand
What is the other strand called for protein-coding genes which is opposite of the DNA strand?
Coding strand - This has the same base sequences as the resulting mRNA, except that uracil replaces thymine inside the nucleotides.
