Part 1: Genetics – From Genes to Proteins, Mutations (Chapter 10)
Overview: Genetic information in DNA is transcribed to RNA and then translated into the amino acid sequence of a Protein.
A) Step 1 - Transcription: During the process of transcription, the information in the DNA codons of a gene is transcribed into RNA.
Suppose that gene X has the DNA base sequence 3’-TACCCTTTAGTAGCCACT-5’.
Question: What would be the base sequence of RNA after transcription occurs? Turn this in.
(In this particular example, assume that the RNA product does not require processing to become mRNA. In other words, the transcribed RNA becomes the mRNA sequence.)
B) Step 2 - Translation: During protein synthesis at the ribosome, the base sequence of the mRNA codons is translated to the amino acid sequence of a protein.
Question: Using the mRNA that you transcribed above, use the genetic code table to determine the resulting amino acid sequence? Turn this in.
And, turn in the answer to these questions:
What is the significance of the first and last codons? What meaning do these codons have for protein synthesis?
C) Mutations: A mutation is defined as a change in the base sequence of DNA. This may occur as a “mistake” in DNA replication, for example.
Suppose that during DNA replication, two mutant DNA sequences are produced as shown below.
For the 2 mutated DNA sequences, you will investigate how these changes might affect the sequence of amino acids in a protein.
Question: For each of the two, you will need to first transcribe the mRNA, and then use the genetic code table to determine the amino acid sequence.
Turn these in, and state whether the protein sequence changes for each.
Question: Then, explain why a change in amino acid sequence might affect protein function. Turn in your answer.
Here is the original sequence, followed by two mutated sequences, 1 and 2:
Original sequence 3'- TACCCTTTAGTAGCCACT-5’
Mutated sequence 1) 3’-TACGCTTTAGTAGCCATT-5'
Mutated sequence 2) 3’-TAACCTTTACTAGGCACT-5’.
Part 2: Inheritance of Traits or Genetic Disorders (Chapter 12)
Bob and Sally recently married. Upon deciding to plan a family, both Sally and Bob find out that they are both heterozygous for cystic fibrosis, but neither of them has symptoms of the disorder.
Set up and complete a Punnett Square for cystic fibrosis for this couple; turn in the Punnett square.
When doing the Punnett Square, C = normal allele; and c = allele for cystic fibrosis.
Note: You can use the Table function in MS Word to create and fill in a Punnett Square.
Questions:
Based on the Punnett square, calculate chances (percentages) for having a healthy child (not a carrier), a child that is a carrier for the cystic fibrosis trait, and a child with cystic fibrosis? Turn in these percentages.
Part 3: Cell division, sexual reproduction and genetic variability (Chapter 11)
Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair; meiosis produces sex cells (gametes) called sperm and eggs.
Although mutations are the ultimate source of genetic variability, both meiosis and sexual reproduction also can contribute to new genetic combinations in offspring.
Question: How do both meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents? Be sure to talk about steps in meiosis that increase variability as well as the process of fertilization.
Part 1: Genetics - From Genes to Proteins, Mutations (Chapter 10)
A) Step 1 - Transcription: During the process of transcription, the information in the DNA codons of a gene is transcribed into RNA.
To transcribe the DNA base sequence 3’-TACCCTTTAGTAGCCACT-5' into RNA, we need to replace each base with its complementary base in RNA.
DNA sequence: 3’-TACCCTTTAGTAGCCACT-5'
RNA sequence: 5’-AUGGGAAAUCAUCGGUGA-3'
B) Step 2 - Translation: During protein synthesis at the ribosome, the base sequence of the mRNA codons is translated to the amino acid sequence of a protein.
Using the mRNA sequence from step A above, we can use the genetic code table to determine the resulting amino acid sequence.
mRNA sequence: 5’-AUGGGAAAUCAUCGGUGA-3'
From the genetic code table:
AUG - Methionine (START codon)
GGA - Glycine
AAU - Asparagine
CAU - Histidine
CGG - Arginine
UGA - Stop codon
The resulting amino acid sequence would be: Methionine-Glycine-Asparagine-Histidine-Arginine.
The first codon (AUG) serves as the START codon, indicating the beginning of translation and the incorporation of Methionine. The last codon (UGA) is a STOP codon, indicating the end of translation and the termination of protein synthesis.
C) Mutations: A mutation is defined as a change in the base sequence of DNA. This may occur as a "mistake" in DNA replication, for example.
For each of the mutated DNA sequences, we need to transcribe the mRNA and then use the genetic code table to determine the amino acid sequence.
Mutated sequence 1: 3’-TACGCTTTAGTAGCCATT-5’
Transcribed mRNA sequence: 5’-AUGCGAAAUCAUCGGUAA-3’
From the genetic code table:
AUG - Methionine (START codon)
CGA - Arginine
AAU - Asparagine
CAU - Histidine
GGU - Glycine
AA - Lysine
The resulting amino acid sequence would be: Methionine-Arginine-Asparagine-Histidine-Glycine-Lysine.
The protein sequence changes compared to the original sequence.
Mutated sequence 2: 3’-TAACCTTTACTAGGCACT-5’
Transcribed mRNA sequence: 5’-AUUGGAAAUCAUCCGUCA-3’
From the genetic code table:
AUU - Isoleucine
GGA - Glycine
AAU - Asparagine
CAU - Histidine
CCG - Proline
UCA - Serine
The resulting amino acid sequence would be: Isoleucine-Glycine-Asparagine-Histidine-Proline-Serine.
The protein sequence changes compared to the original sequence.
A change in the amino acid sequence might affect protein function because amino acids determine the structure and shape of proteins. Any alteration in the sequence can disrupt the folding and stability of the protein, affecting its function. Changes in critical regions or functional domains can impair the protein's ability to interact with other molecules or carry out its specific role in cellular processes.
Part 2: Inheritance of Traits or Genetic Disorders (Chapter 12)
Punnett Square for cystic fibrosis (C = normal allele; c = allele for cystic fibrosis):
| C | c |
-------|----------|----------|
C | CC | Cc |
-------|----------|----------|
C | Cc | cc |
-------|----------|----------|
Chances (percentages) for having:
- A healthy child (not a carrier): CC genotype - 25%
- A child that is a carrier for the cystic fibrosis trait: Cc genotype - 50%
- A child with cystic fibrosis: cc genotype - 25%
Part 3: Cell division, sexual reproduction, and genetic variability (Chapter 11)
Both meiosis and sexual reproduction (fertilization) contribute to new genetic combinations in offspring.
Meiosis is a process that produces sex cells (gametes) with half the number of chromosomes (haploid). During meiosis, homologous chromosomes pair up and undergo genetic recombination (crossing over) in Prophase I. This leads to the exchange of genetic material between homologous chromosomes, resulting in new combinations of genes. Additionally, during Anaphase I and Anaphase II, the separation and random assortment of chromosomes further increase genetic variability.
Sexual reproduction, specifically fertilization, combines genetic material from two parents. Each parent contributes a gamete with a unique combination of genes, resulting in a genetically diverse offspring. The fusion of gametes during fertilization creates a zygote with a complete set of chromosomes (diploid), which then undergoes mitosis for growth and development.
Thus, both meiosis and sexual reproduction introduce genetic variability through genetic recombination, random assortment of chromosomes, and the combination of genetic material from two parents during fertilization. This creates offspring that differ genetically from their parents.
A) Step 1 - Transcription: During transcription, the base sequence of DNA is transcribed into RNA. To determine the base sequence of RNA after transcription, we need to remember that during transcription, the RNA strand is complementary to the DNA strand, but with uracil (U) instead of thymine (T).
In this example, the DNA sequence is 3’-TACCCTTTAGTAGCCACT-5’. To transcribe this, we replace T with U and write the complementary RNA strand:
5'-AUGGGAAAUCAUCGGUGA-3'
So, the base sequence of RNA after transcription is 5'-AUGGGAAAUCAUCGGUGA-3'.
B) Step 2 - Translation: During translation, the mRNA codons are translated into the amino acid sequence of a protein using the genetic code table. We can use the mRNA sequence obtained in part A to determine the resulting amino acid sequence.
Using the genetic code table, we read the mRNA sequence in sets of three (codons) and find the corresponding amino acids. Here is the translation using the mRNA sequence from part A:
AUG GGA AAU CAU CGG UGA
Start codon: AUG (codes for Methionine)
GGA (codes for Glycine)
AAU (codes for Asparagine)
CAU (codes for Histidine)
CGG (codes for Arginine)
UGA (stop codon)
So, the resulting amino acid sequence is Methionine (Met) - Glycine (Gly) - Asparagine (Asn) - Histidine (His) - Arginine (Arg).
The first codon (AUG) is the start codon, and it codes for the amino acid Methionine. The last codon (UGA) is the stop codon, and it signals the end of protein synthesis. It does not code for any amino acid and serves as a termination signal.
C) Mutations: Mutations are changes in the base sequence of DNA. To determine the RNA and amino acid sequences for the two mutated DNA sequences provided, we follow the same process as in parts A and B.
Mutated sequence 1: 3’-TACGCTTTAGTAGCCATT-5'
Transcribed RNA: 5’-AUGCGAAAUCAUCGGUAA-3'
Amino acid sequence: Methionine (Met) - Arginine (Arg) - Isoleucine (Ile) - Isoleucine (Ile) - Glycine (Gly) - Stop
Mutated sequence 2: 3’-TAACCTTTACTAGGCACT-5’
Transcribed RNA: 5’-AUUGGAAAUCAUCCGUCA-3'
Amino acid sequence: Isoleucine (Ile) - Glycine (Gly) - Asparagine (Asn) - Histidine (His) - Arginine (Arg) - Serine (Ser) - Stop
For both mutated sequences, the protein sequence changes. The original sequence codes for the amino acid sequence Methionine - Glycine - Asparagine - Histidine - Arginine, while the mutated sequences result in different amino acids being inserted, which alters the protein structure.
A change in the amino acid sequence can affect protein function because proteins rely on specific amino acid sequences to fold into their functional three-dimensional structures. A change in even a single amino acid can disrupt the folding and shape of the protein, leading to loss of function or altered function. In other cases, a mutation may introduce a premature stop codon, resulting in a truncated protein that lacks important functional domains. These changes can impact the protein's ability to carry out its normal biological functions.