Different versions of the same gene are called different alleles. These different alleles share the same general sequence of nitrogenous bases, but they differ in at least one base in the sequence.
Different alleles can result in different characteristics as follows:
Differences in the nitrogenous base sequence in the gene…
…result in differences in the base sequence in mRNA…
…result in differences in the amino acid sequence in the protein…
…result in differences in the structure and function of the protein…
…result in differences in a person’s characteristics.
For example, if a person has an allele that codes for a normal version of an enzyme to make melanin, this person will have typical skin and hair pigmentation. In contrast, if a person’s alleles code for an irregular version of this enzyme, this person’s cells will not be able to make melanin, so this person will have albinism.
mozambique_albinism.jpg
Image: shows Albinism versus typical melanin production in two children from Mozambique.
In this assignment, you will learn about another example: normal versus (vs.) sickle cell hemoglobin.
Each complete hemoglobin protein has more than 100 amino acids. Sickle cell hemoglobin and normal hemoglobin differ in only a single amino acid. This difference in a single amino acid results in the very different properties of sickle cell hemoglobin, compared to normal hemoglobin.
Sickle cell anemia is a genetically inherited red blood cell (RBC) disorder in which there aren’t enough healthy RBCs to carry oxygen throughout your body.
Normally, the flexible, round RBCs move easily through blood vessels.
In sickle cell anemia, the RBCs are shaped like sickles or crescent moons.
These rigid, sticky cells can get stuck in small blood vessels and capillaries, which can slow or block blood flow and oxygen to parts of the body, causing pain and damage to body organs.
In addition, sickle-shaped RBCs do not live nearly as long as normal red blood cells, so the person does not have enough RBCs, causing anemia.
There is currently no cure for most people with sickle cell anemia, but treatments like regular blood transfusions of normal RBCs can relieve pain and help prevent complications associated with the disease.
human-red-blood-cells-sickle-cell-anemia.jpg
Image: shows normal red blood cells (RBCs) on the left and sickle RBCs on the right.
In the table below, compare the DNA sequence for the Beginning of the Normal Hemoglobin Gene to the Beginning of the Sickle Cell Hemoglobin Gene.
What similarities do you observe?
What difference(s) do you observe?
Beginning of Normal Hemoglobin Gene
CACGTAGACTGAGGACTC
Transcription produces:
codon 1
codon 2
codon 3
codon 4
codon 5
codon 6
Beginning of Normal Hemoglobin mRNA
Translation produces:
amino acid 1
amino acid 2
amino acid 3
amino acid 4
amino acid 5
amino acid 6
Beginning of Normal Hemoglobin Protein
Beginning of Sickle Cell Hemoglobin Gene
CACGTAGACTGAGGACAC
Transcription produces:
codon 1
codon 2
codon 3
codon 4
codon 5
codon 6
Beginning of Sickle Cell Hemoglobin mRNA
Translation produces:
amino acid 1
amino acid 2
amino acid 3
amino acid 4
amino acid 5
amino acid 6
Beginning of Sickle Cell Hemoglobin Protein
Complete the table above on a separate piece of paper.
To complete the table, fill in the following rows:
Beginning of Normal Hemoglobin mRNA
Beginning of Normal Hemoglobin Protein
Beginning of Sickle Cell Hemoglobin mRNA
Beginning of Sickle Cell Hemoglobin Protein
You will need to reference this mRNA codon and matching amino acid key to complete the table above:
mRNA codon
Amino acid
ACU
Threonine (Thr)
CAU
Histidine (His)
CCU
Proline (Pro)
CUG
Leucine (Leu)
GAG
Glutamic acid (Glu)
GUG
Valine (Val)
Answer the following questions. This will be your submission. Please number your answers in your submission. Two points for each correct answer for up to ten points.
What is the difference in the DNA sequence of the normal hemoglobin gene vs. the sickle cell hemoglobin gene?
What is the difference in the mRNA codon sequence of the normal hemoglobin vs. the sickle cell hemoglobin?
What is the difference in the amino acid sequence of the normal hemoglobin vs. the sickle cell hemoglobin?
How does your DNA determine whether you develop sickle cell anemia?
Considering that we are all made up of the same four nitrogenous bases in our DNA, the same four nitrogenous bases in our RNA, and the same 20 amino acids in our proteins, why are we so different from each other? Are we so different from each other?
