Expression of genes
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Questions and Answers

What describes the process by which proteins attain their biologically active form?

  • Folding (correct)
  • Denaturation
  • Condensation
  • Hydrolysis

Which level of protein structure involves the linear order of amino acids?

  • Quaternary structure
  • Tertiary structure
  • Secondary structure
  • Primary structure (correct)

What type of bond links amino acids together in a polypeptide chain?

  • Disulfide bond
  • Peptide bond (correct)
  • Hydrogen bond
  • Ionic bond

Which statement about hemoglobin is true?

<p>It binds iron to transport oxygen. (D)</p> Signup and view all the answers

What is the main consequence of a protein becoming denatured?

<p>It loses its biological activity. (B)</p> Signup and view all the answers

How many types of amino acids do proteins consist of?

<p>20 (B)</p> Signup and view all the answers

What determines the unique properties of each amino acid?

<p>Sidechain, R (D)</p> Signup and view all the answers

Which level of protein structure involves the association of multiple polypeptide chains?

<p>Quaternary structure (C)</p> Signup and view all the answers

Which of the following describes a characteristic of enzymes?

<p>They speed up chemical reactions. (C)</p> Signup and view all the answers

What type of interaction stabilizes tertiary structure in proteins?

<p>Hydrogen bonding between sidechains (D)</p> Signup and view all the answers

What is the primary function of the polyA tail in mRNA?

<p>Stabilizes the mRNA molecule (C)</p> Signup and view all the answers

What process occurs during splicing of mRNA?

<p>Concatenation of exons to form mature mRNA (A)</p> Signup and view all the answers

What role does tRNA play in the translation process?

<p>Brings amino acids to the ribosome matching the mRNA codons (A)</p> Signup and view all the answers

In the ribosome, which sites are involved in the elongation of the polypeptide chain?

<p>A, P, E sites (B)</p> Signup and view all the answers

What characterizes wild type mutations?

<p>Normal nucleotide sequence (D)</p> Signup and view all the answers

Which of the following describes a missense mutation?

<p>Changes one amino acid for another (C)</p> Signup and view all the answers

What is a common effect of frameshift mutations?

<p>Premature stop codons introduced soon after (A)</p> Signup and view all the answers

Which statement accurately describes the redundancy in the genetic code?

<p>Many amino acids are specified by multiple codons. (C)</p> Signup and view all the answers

How does tRNA become charged with the appropriate amino acid?

<p>Through the action of tRNA synthetase enzymes (C)</p> Signup and view all the answers

In the process of transcription, at which stage does RNA polymerase bind to the DNA?

<p>Initiation (B)</p> Signup and view all the answers

Which component of protein synthesis acts as the enzyme linking amino acids together?

<p>Ribosome (A)</p> Signup and view all the answers

What is the function of the A site in the ribosome during translation?

<p>Binds incoming tRNA with the corresponding amino acid (D)</p> Signup and view all the answers

What is the primary function of mRNA capping in eukaryotes?

<p>To protect the mRNA from degradation. (A)</p> Signup and view all the answers

Which of the following statements about the genetic code is false?

<p>A codon consists of two nucleotides. (C)</p> Signup and view all the answers

Which characteristic is true for RNA polymerase during transcription?

<p>It detaches from the DNA strand at the termination stage. (C)</p> Signup and view all the answers

Which statement correctly explains the directional flow of genetic information?

<p>Information flows from DNA to RNA to protein. (B)</p> Signup and view all the answers

How many stop codons are present in the genetic code?

<p>3 (C)</p> Signup and view all the answers

What is the role of transcription factors (TFs) in the initiation of transcription?

<p>To assist RNA polymerase in binding to the promoter. (C)</p> Signup and view all the answers

During transcription, which nucleobase pairs with adenine in the RNA strand?

<p>Uracil (B)</p> Signup and view all the answers

Which of the following is not a stage of transcription?

<p>Enrichment (D)</p> Signup and view all the answers

What is the primary consequence of a single mutation in the DNA that affects hemoglobin?

<p>Clumping of hemoglobin and reduced oxygen transport (D)</p> Signup and view all the answers

Which of the following accurately lists the levels of protein structure?

<p>Primary, secondary, tertiary, and quaternary (D)</p> Signup and view all the answers

What phenomenon occurs if a frameshift mutation is a multiple of 3?

<p>No significant effect on protein structure (B)</p> Signup and view all the answers

What role does RNA polymerase play in gene expression?

<p>Facilitates the transcription of DNA into mRNA (B)</p> Signup and view all the answers

In the context of mutations, what is primarily affected in protein coding genes?

<p>The sequence of amino acids in proteins (B)</p> Signup and view all the answers

Which process involves the translation of mRNA into proteins?

<p>Translation (B)</p> Signup and view all the answers

What is a result of sickle cell hemoglobin in red blood cells?

<p>Results in stretched, sickle-shaped red blood cells (C)</p> Signup and view all the answers

What is the correct flow of genetic information as per the central dogma?

<p>DNA – RNA – Protein (B)</p> Signup and view all the answers

What occurs in post-transcriptional processing?

<p>Introns are removed and exons are spliced together (B)</p> Signup and view all the answers

Which of the following best defines a gene?

<p>A sequence of nucleotides that codes for a protein (D)</p> Signup and view all the answers

Flashcards

Protein Structure

The specific arrangement of amino acids in a protein, which determines its function.

Protein Folding

The process by which a protein assumes its three-dimensional shape, crucial for its activity.

Primary Structure

The linear sequence of amino acids in a protein.

Secondary Structure

The local arrangement of amino acid chains, stabilized by hydrogen bonds.

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Tertiary Structure

The overall three-dimensional shape of a protein, resulting from interactions of side chains.

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Quaternary Structure

The arrangement of multiple polypeptide chains in a protein with multiple subunits.

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Amino Acid

The fundamental building block of a protein, with a unique side chain.

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Peptide Bond

The covalent bond linking amino acids in a protein chain.

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Polypeptide Chain

A chain of amino acids linked by peptide bonds.

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Protein Function

The role a protein plays in a biological system, determined by its structure.

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Central dogma of molecular biology

Directional flow of genetic information from DNA to RNA to protein.

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Genetic code

A set of rules that translate DNA sequences into proteins.

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Codons

Groups of three nucleotides that specify a particular amino acid.

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Transcription

Process of copying a DNA sequence into an RNA sequence.

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RNA polymerase

Enzyme that builds RNA molecules during transcription.

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Transcription initiation

The starting point of copying in the transcription process.

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Transcription elongation

The process of adding nucleotides to the RNA strand during transcription.

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Transcription termination

End of transcription.

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mRNA capping

Protective modification added to the 5' end of mRNA in eukaryotes.

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Genetic code redundancy

Multiple codons can code for the same amino acid.

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Sickle Cell Hemoglobin

A genetic disorder caused by a mutation in the gene for hemoglobin, leading to deformed red blood cells.

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Hemoglobin Mutation

A change in the DNA sequence that alters the amino acid sequence of hemoglobin, resulting in different properties.

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What does a frameshift mutation do?

A frameshift mutation inserts or deletes nucleotides in a gene, shifting the reading frame and potentially altering the amino acid sequence drastically.

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What is a multiple-of-3 frameshift?

A frameshift mutation that adds or deletes nucleotides in multiples of three, maintaining the reading frame but still potentially affecting the protein.

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Mutation and disease

Changes in DNA sequences, known as mutations, can lead to altered protein function and potentially cause genetic diseases.

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Central dogma

The fundamental principle describing the flow of genetic information from DNA to RNA to protein.

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Translation

The process of decoding an mRNA sequence into a protein, using ribosomes and tRNA molecules.

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tRNA, ribosomes, export

These components are involved in the process of translation, where tRNA brings amino acids to the ribosome for protein synthesis, and the completed protein is eventually exported to its destination.

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polyA tail

A string of adenine nucleotides added to the 3' end of mRNA after transcription. It protects the mRNA from degradation and helps it bind to ribosomes for translation.

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RNA splicing

The process that removes non-coding regions (introns) from pre-mRNA and joins the coding regions (exons) together, creating a mature mRNA molecule ready for translation.

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Introns

Non-coding regions within a gene that are removed during RNA splicing. They are transcribed but not translated.

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tRNA

Transfer RNA, a molecule that carries a specific amino acid to the ribosome during translation. It has an anticodon that matches the codon on the mRNA, ensuring the correct amino acid is added to the growing polypeptide chain.

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Ribosome

A complex cellular machine responsible for protein synthesis. It reads the mRNA sequence and links amino acids together to form a polypeptide chain.

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What is the role of the ribosome's A site?

The A site is the binding site for the tRNA carrying the next amino acid to be added to the growing polypeptide chain.

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What is the role of the ribosome's P site?

The P site holds the tRNA carrying the growing polypeptide chain. Peptide bonds are formed between amino acids in the P site.

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What is the role of the ribosome's E site?

The E site is the exit site for empty tRNAs that have delivered their amino acids.

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What is the difference between a wild type and a mutation?

A wild type sequence refers to the normal, unaltered sequence of a gene. A mutation is any change in that sequence, such as a substitution or insertion/deletion.

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Study Notes

Protein Structure and Function

  • Proteins perform diverse functions based on their structures.
  • Protein structures enable a wide range of functions including digestion (enzymes), storage (ovalbumin), defense (antibodies), transport (hemoglobin), signaling (receptors), structural support (keratin), coordination (insulin), and movement (actin-myosin).
  • Protein function depends on biochemical properties determined by their structure.
  • Antibody protein surfaces match target antigens enabling recognition.
  • Hemoglobin protein pockets fit heme chemicals, enabling iron to transport oxygen.

Protein Folding

  • Folded proteins have a final and stable structure and are active.
  • Denatured proteins are unfolded and inactive.
  • Proteins must fold to be biologically active.

Protein Structure Levels

  • Primary structure: The linear order of amino acids in a polypeptide chain.
  • Secondary structure: Hydrogen bonding between nearby amino acids in the polypeptide backbone forming structures like alpha-helices and beta-sheets.
  • Tertiary structure: Interactions between side chains stabilize the protein into a 3D shape (often a globular shape) influencing the protein's function.
  • Quaternary structure: Close association of two or more polypeptide chains assembling into a larger functional unit.

Proteins from Amino Acids

  • Proteins are polymers of amino acids.
  • Amino acids have a common structure:
    • An amino group
    • A carboxyl group
    • A central alpha carbon
    • A variable side chain (R group)
  • The unique side chains impart different properties to each amino acid type.

Amino Acid Polymers

  • Amino acid polymers link via peptide bonds.
  • Peptide bonds form between amino acids in the backbone.
  • Proteins consist of 50-5000 amino acids.
  • Polypeptide chains have N-terminus and C-terminus.

20 Amino Acid Types

  • Side chains confer unique properties to the different amino acid types
  • Proteins have a chemical toolkit of 20 amino acids.
  • Categorized into chemical types: hydrophobic, non-polar; nonpolar; polar; charged hydrophilic.

Central Dogma of Molecular Biology

  • The central dogma describes the flow of genetic information, from DNA to RNA to protein.
  • "Once sequence information has passed into protein it cannot get out." - Crick, 1956
  • DNA -> RNA -> Protein

Genetic Code: DNA Translates to Protein

  • Universal code: the genetic code is the same in all living organisms
  • Codons: 20 amino acids but 4 bases, so it takes multiple bases to encode each amino acid.
  • The code uses groups of three nucleotides, codons, each determining a specific amino acid.
  • Each codon has multiple possibilities in each of its three nucleotide positions meaning there are 64 possible amino acid codons.

Genetic Code is Redundant

  • For most amino acids, there is more than one codon leading to redundancy.
  • There are 3 stop codons and 1 start codon which is shared.

Transcription: Making mRNA

  • Initiation: RNA polymerase binds to a start point and transcription factors assist.
  • Elongation: RNA polymerase moves along the DNA template strand synthesizing RNA in the 5' to 3' direction. Uracil (U) in RNA pairs with adenine (A) in DNA;
  • Termination: RNA polymerase detaches from the DNA template completing the transcription process enabling it to restart another cycle.

RNA Post-Transcriptional Processing

  • Occurs only in eukaryotes
  • Capping: A modified guanine nucleotide is added to the 5' end of the pre-mRNA in a protective role.
  • Polyadenylation: 50-250 adenine nucleotides are added to the 3' end of the pre-mRNA creating a poly(A) tail facilitating stabilization.
  • Splicing: Introns (non-coding segments) are removed and exons (coding segments) are joined forming mature mRNA containing only protein-coding sequences.

Translation: mRNA to Protein

  • mRNA processed transcript acts as a blueprint of the sequence of codons.
  • tRNA adapter holds matching anticodon and complementary amino acids.
  • Ribosome enzymes chain amino acids into polypeptides.
  • tRNA synthetase enzymes charge tRNA.
  • Ribosomes bind mRNA and tRNAs to catalyze translation.

Mutations and Protein Function

  • Mutations are changes in a gene's coding sequence.
  • Substitution mutations change nucleotides, leading to different outcomes: silent mutation (same amino acid), missense mutation (different amino acid), nonsense mutation (stop codon).
  • Frameshift mutations cause insertions/deletions, resulting in premature stop codons or many incorrect amino acids.
  • Mutations can cause genetic diseases; e.g., sickle cell anemia.

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