Podcast
Questions and Answers
How does the sequence of amino acids primarily influence the properties of a protein?
How does the sequence of amino acids primarily influence the properties of a protein?
- By dictating the three-dimensional folding and therefore functional specificity of the protein. (correct)
- By regulating the protein's interaction with chaperone molecules.
- By determining the rate at which the protein is synthesized in the ribosome.
- By influencing the binding affinity of the protein to DNA.
How might a mutation in a gene's DNA sequence affect the final protein product?
How might a mutation in a gene's DNA sequence affect the final protein product?
- It will invariably lead to a non-functional protein, halting cellular processes.
- It could result in a different amino acid sequence, potentially altering protein structure and function. (correct)
- It generally results in a beneficial adaptation by enhancing protein efficiency.
- Only mutations in non-coding regions like introns can affect the protein's stability.
Which of the following best describes the significance of start and stop codons in the genetic code?
Which of the following best describes the significance of start and stop codons in the genetic code?
- They define where the ribosome initially binds to mRNA.
- They act as enhancers and silencers, regulating the transcription rate of genes.
- They only serve to prevent the ribosome from prematurely terminating translation.
- They specify the beginning and end points for the translation of a gene into a polypeptide sequence. (correct)
Considering that there are 64 possible triplet codons and only 20 amino acids, what feature of the genetic code does this illustrate?
Considering that there are 64 possible triplet codons and only 20 amino acids, what feature of the genetic code does this illustrate?
What would be the most likely outcome if a cell's DNA polymerase lacked the ability to proofread during replication?
What would be the most likely outcome if a cell's DNA polymerase lacked the ability to proofread during replication?
Which of the following cellular processes is most directly affected by the primary structure of a protein?
Which of the following cellular processes is most directly affected by the primary structure of a protein?
If a tRNA molecule responsible for carrying glycine to the ribosome is mutated such that it now carries alanine, what is the likely consequence?
If a tRNA molecule responsible for carrying glycine to the ribosome is mutated such that it now carries alanine, what is the likely consequence?
A particular gene sequence reads 'ATT' at the beginning of its coding region. How might this affect protein synthesis?
A particular gene sequence reads 'ATT' at the beginning of its coding region. How might this affect protein synthesis?
How does the non-overlapping nature of the genetic code contribute to the fidelity of protein synthesis?
How does the non-overlapping nature of the genetic code contribute to the fidelity of protein synthesis?
If a sequence of DNA is found to have a high proportion of codons that are rarely used in the cell, what might be the likely effect on translation?
If a sequence of DNA is found to have a high proportion of codons that are rarely used in the cell, what might be the likely effect on translation?
Which of the following provides the strongest evolutionary rationale for the degeneracy of the genetic code?
Which of the following provides the strongest evolutionary rationale for the degeneracy of the genetic code?
During transcription, RNA polymerase synthesizes mRNA using the template strand of DNA. What would be the consequence if RNA polymerase lost its ability to identify and bind to promoter regions on the DNA?
During transcription, RNA polymerase synthesizes mRNA using the template strand of DNA. What would be the consequence if RNA polymerase lost its ability to identify and bind to promoter regions on the DNA?
Considering the process of translation, what would be the most immediate consequence if a cell lacked the enzyme that attaches amino acids to their corresponding tRNA molecules?
Considering the process of translation, what would be the most immediate consequence if a cell lacked the enzyme that attaches amino acids to their corresponding tRNA molecules?
A scientist introduces a chemical into a cell culture that prevents the formation of the peptide bond during translation. What is the most likely direct consequence of this?
A scientist introduces a chemical into a cell culture that prevents the formation of the peptide bond during translation. What is the most likely direct consequence of this?
A hypothetical mutation in a gene results in a mRNA molecule that lacks a stop codon. What would be the most likely consequence of this mutation during translation?
A hypothetical mutation in a gene results in a mRNA molecule that lacks a stop codon. What would be the most likely consequence of this mutation during translation?
Imagine a mutation occurs in the promoter region of a gene that codes for a crucial enzyme. This mutation drastically reduces the affinity of RNA polymerase for the promoter. What is the most probable outcome?
Imagine a mutation occurs in the promoter region of a gene that codes for a crucial enzyme. This mutation drastically reduces the affinity of RNA polymerase for the promoter. What is the most probable outcome?
A certain eukaryotic gene contains five exons and four introns. A mutation occurs that prevents the splicing of one of the introns. What would be the most likely effect of this mutation on the protein product of the gene?
A certain eukaryotic gene contains five exons and four introns. A mutation occurs that prevents the splicing of one of the introns. What would be the most likely effect of this mutation on the protein product of the gene?
A researcher is studying a newly discovered gene and identifies a single nucleotide substitution mutation in the coding region. Through protein analysis, they determine that the amino acid sequence of the resulting protein is identical to the wild-type protein. What type of mutation is most likely responsible for this observation?
A researcher is studying a newly discovered gene and identifies a single nucleotide substitution mutation in the coding region. Through protein analysis, they determine that the amino acid sequence of the resulting protein is identical to the wild-type protein. What type of mutation is most likely responsible for this observation?
Considering the different types of mutations, which mutation has the potential to cause the most significant change in the structure of a protein?
Considering the different types of mutations, which mutation has the potential to cause the most significant change in the structure of a protein?
A particular genetic disease is caused by a nonsense mutation in a gene. What is the most direct effect of this type of mutation on the production of the related protein?
A particular genetic disease is caused by a nonsense mutation in a gene. What is the most direct effect of this type of mutation on the production of the related protein?
Flashcards
What is a gene?
What is a gene?
A sequence of nucleotides in DNA that codes for a specific polypeptide.
DNA Molecule
DNA Molecule
A molecule containing many genes that determine traits.
What is a polypeptide?
What is a polypeptide?
A chain of amino acids; the building block of proteins.
What are proteins?
What are proteins?
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Primary Structure
Primary Structure
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What is a triplet code?
What is a triplet code?
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Gene's Role
Gene's Role
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Start/Stop Signals
Start/Stop Signals
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Universal Genetic Code
Universal Genetic Code
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Codon
Codon
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Degenerate Genetic Code
Degenerate Genetic Code
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Gene Definition
Gene Definition
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Transcription
Transcription
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Translation
Translation
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Template Strand
Template Strand
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Non-Template Strand
Non-Template Strand
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Exons
Exons
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Introns
Introns
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Gene Mutation
Gene Mutation
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Study Notes
- A gene is a nucleotide sequence within a DNA molecule that codes for a specific polypeptide
- Polypeptides are proteins made of amino acids linked together
- A protein's shape and function depend on its amino acid sequence, known as the primary structure
- Genes control protein structure and function by determining the amino acid sequence during protein synthesis
The Universal Genetic Code
- A gene's DNA nucleotide base code is a triplet code
- Each triplet codes for one amino acid
- CAG codes for valine, TTC codes for lysine, GAC codes for leucine and CCG codes for glycine
- Some triplets signal the start (TAC – methionine)and stop of genes, ensuring correct reading of DNA
- The code is non-overlapping, ensuring correct amino acid sequences
- With four bases, there are 64 possible triplets, but only 20 amino acids, leading to code degeneracy, where multiple triplets code for the same amino acid
- Degeneracy limits the impact of mutations
- The universality of the genetic code means the same triplets code for the same amino acids across nearly all organisms, allowing genetic information to be transferable between species
Constructing Polypeptides: Transcription & Translation
- Protein synthesis occurs in two stages: transcription and translation
Transcription
- Transcription occurs in the cell nucleus
- A DNA molecule unwinds, exposing the gene to be transcribed
- A complementary mRNA molecule is built from the gene's code
- DNA triplets are transcribed into mRNA codons
- Single-stranded mRNA can pass through nuclear envelope pores
- Free RNA nucleotides pair with complementary bases on the DNA template strand
- RNA polymerase bonds the sugar-phosphate groups of RNA nucleotides, forming the mRNA backbone
- Once the gene is transcribed, the mRNA detaches, and the DNA re-forms
- The mRNA then exits the nucleus
Translation
- Translation happens in the cell cytoplasm
- mRNA attaches to a ribosome
- Free tRNA molecules in the cytoplasm have an anticodon at one end and a specific amino acid binding site at the other
- At least 20 different tRNA molecules exist, each with a specific anticodon for a specific amino acid
- tRNA molecules bind to their specific amino acids and transport them to the mRNA on the ribosome
- The tRNA anticodon pairs with the complementary mRNA codon
- Two tRNA molecules fit on the ribosome at once, bringing amino acids side by side
- A peptide bond forms between the two amino acids
- This continues until a stop codon is reached which signals the end of translation and complete the amino acid chain to form a polypeptide
Template & Non-Template Strands
- During transcription, the DNA section with the gene unwinds
- RNA nucleotides pair with bases on one DNA strand, called the template or transcribed strand
- This strand is transcribed into mRNA
- RNA polymerase joins the RNA nucleotides to form the mRNA backbone
- The non-template or non-transcribed strand isn't used in transcription
Post-Transcriptional Modification
- Eukaryotic genes have coding (exons) and non-coding (introns) sequences
- Exons are translated into amino acids
- Introns are not translated
- During transcription, both exons and introns are transcribed into a primary transcript
- Introns are removed, and exons are joined to form mature mRNA in a process called splicing
- This modification occurs after transcription but before translation
Gene Mutations & Their Effect on Polypeptides
- Gene mutation refer to changes in the DNA base sequence that may alter a polypeptide
- Mutations occur continuously
- DNA base sequence determines the amino acid sequence of a protein, gene mutations can sometimes lead to a change in the polypeptide coded for
- Most mutations don't change the polypeptide or only change it slightly because the genetic code is degenerate
Insertion of nucleotides
- Insertion mutation happens when a nucleotide is randomly inserted into the DNA sequence
- The original coded amino is changed as a new, different triplet of bases is created
- Insertion also has a knock-on effect by changing the triplets further on in the DNA sequence, also known as a frameshift mutation
- Frameshift mutations may dramatically change the amino acid sequence produced from this gene and consequently the ability of the polypeptide to function
Deletion of nucleotides
- Deletion mutation happens when a nucleotide is randomly deleted from the DNA sequence
- The original coded amino is changed
- Similar to insertion, deletion changes the groups of three bases further on in the DNA sequence, also known as a frameshift mutation
- The amino acid sequence produced from this gene may dramatically change which will affect the ability of the polypeptide to function
Substitution of nucleotides
- Substitution mutation occurs when a base in the DNA sequence is randomly swapped for a different base
- Substitution mutation will only change the amino acid for the triplet in which the mutation occurs
- Substitution mutations include:
- Silent mutations don't alter the amino acid sequence due to the degeneracy of the genetic code
- Missense mutations alter a single amino acid in the polypeptide chain. Sickle cell anaemia is an example
- Nonsense mutations create a premature stop codon, resulting in an incomplete polypeptide chain and altered protein structure and function. Cystic fibrosis is an example
The effect of gene mutations on polypeptides
- Most mutations do not alter the polypeptide or only alter it slightly so that its appearance or function is not changed
- However, some mutations code for a significantly altered polypeptide with a different shape
- The ability of the protein to perform its function may be affected
- If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site
- A structural protein may lose its strength if its shape changes
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Description
Explore the universal genetic code where DNA nucleotide triplets code for specific amino acids, forming polypeptides. Genes determine amino acid sequence, influencing protein structure/function. Degeneracy in the genetic code limits mutation impacts.
