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Questions and Answers
What is the primary function of antibodies in the immune system?
What is the primary function of antibodies in the immune system?
Which type of protein is involved in accelerating chemical reactions without changing the equilibrium?
Which type of protein is involved in accelerating chemical reactions without changing the equilibrium?
How is the primary structure of a protein determined?
How is the primary structure of a protein determined?
What role do porins play in bacterial cells?
What role do porins play in bacterial cells?
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What is the significance of the active site in enzymes?
What is the significance of the active site in enzymes?
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What is a characteristic of secondary structure in proteins?
What is a characteristic of secondary structure in proteins?
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What role do chaperones play in protein folding?
What role do chaperones play in protein folding?
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How are tertiary structures primarily stabilized?
How are tertiary structures primarily stabilized?
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What is the quaternary structure of a protein?
What is the quaternary structure of a protein?
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Which of the following is true regarding post-translational modifications?
Which of the following is true regarding post-translational modifications?
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What is the primary function of ubiquitination in proteins?
What is the primary function of ubiquitination in proteins?
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Where do hydrophobic amino acids generally localize in the tertiary structure of a protein?
Where do hydrophobic amino acids generally localize in the tertiary structure of a protein?
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Which of the following best describes the role of DNA in hereditary information?
Which of the following best describes the role of DNA in hereditary information?
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What conclusion did the Sutton-Boveri theory support regarding chromosomes?
What conclusion did the Sutton-Boveri theory support regarding chromosomes?
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What describes the process of phosphorylation in proteins?
What describes the process of phosphorylation in proteins?
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What do signal sequences in proteins primarily indicate?
What do signal sequences in proteins primarily indicate?
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What is the main function of ribosomes in relation to membrane proteins?
What is the main function of ribosomes in relation to membrane proteins?
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How do different amino acids behave when interacting with water?
How do different amino acids behave when interacting with water?
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What is an example of a protein with a quaternary structure?
What is an example of a protein with a quaternary structure?
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What is the primary role of telomeres in eukaryotic chromosomes?
What is the primary role of telomeres in eukaryotic chromosomes?
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What feature distinguishes the leading strand from the lagging strand in DNA replication?
What feature distinguishes the leading strand from the lagging strand in DNA replication?
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Which type of DNA binding protein specifically cuts DNA at palindromic sequences?
Which type of DNA binding protein specifically cuts DNA at palindromic sequences?
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How do plasmids benefit bacteria?
How do plasmids benefit bacteria?
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Which enzyme unwinds the double helix during DNA replication?
Which enzyme unwinds the double helix during DNA replication?
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What is the result of the Meselson-Stahl experiment after bacteria are transferred to 14N media?
What is the result of the Meselson-Stahl experiment after bacteria are transferred to 14N media?
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What is produced during the initial steps of DNA replication before DNA polymerase can start working?
What is produced during the initial steps of DNA replication before DNA polymerase can start working?
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What major problem does erosion of genetic material at the ends of linear chromosomes cause?
What major problem does erosion of genetic material at the ends of linear chromosomes cause?
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What functions are associated with DNA binding proteins?
What functions are associated with DNA binding proteins?
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What evidence from the Meselson-Stahl experiment negated the conservative model of DNA replication?
What evidence from the Meselson-Stahl experiment negated the conservative model of DNA replication?
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What is a characteristic of prokaryotic genomes compared to eukaryotic genomes?
What is a characteristic of prokaryotic genomes compared to eukaryotic genomes?
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What was established by injecting dead S bacteria into mice along with live R bacteria?
What was established by injecting dead S bacteria into mice along with live R bacteria?
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What common feature do centromeres share across eukaryotic chromosomes?
What common feature do centromeres share across eukaryotic chromosomes?
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What is recognized as the 'transforming principle' in the experiment described?
What is recognized as the 'transforming principle' in the experiment described?
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Which component was shown to be non-infectious in the Hershey and Chase experiment?
Which component was shown to be non-infectious in the Hershey and Chase experiment?
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What describes the synthesis direction of DNA polymerase during replication?
What describes the synthesis direction of DNA polymerase during replication?
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Which of the following enzymes relieves pressure from overwinding ahead of the replication fork?
Which of the following enzymes relieves pressure from overwinding ahead of the replication fork?
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What does Erwin Chargaff's rules state about the composition of DNA?
What does Erwin Chargaff's rules state about the composition of DNA?
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What was a critical finding from X-ray crystallography related to DNA's structure?
What was a critical finding from X-ray crystallography related to DNA's structure?
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What critical feature of DNA structure did Watson and Crick's model introduce?
What critical feature of DNA structure did Watson and Crick's model introduce?
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What determines the virulence of certain bacteria in the context of DNA transfer?
What determines the virulence of certain bacteria in the context of DNA transfer?
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What is one result of the bacteriophage life cycle during infection of E. coli?
What is one result of the bacteriophage life cycle during infection of E. coli?
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Which technique was used to separate and analyze the nucleobase components of DNA?
Which technique was used to separate and analyze the nucleobase components of DNA?
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What occurs due to the antiparallel nature of DNA strands?
What occurs due to the antiparallel nature of DNA strands?
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What is included in the chemical composition of DNA?
What is included in the chemical composition of DNA?
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Which of the following best describes the structure of a chromosome?
Which of the following best describes the structure of a chromosome?
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What is demonstrated by the isotope labeling in the Hershey and Chase experiment?
What is demonstrated by the isotope labeling in the Hershey and Chase experiment?
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Study Notes
Protein Structure and Function
- Proteins are diverse molecules with varied structures and functions, including hormones, antibodies, DNA-binding proteins, and enzymes.
- Proteins form structural components like microtubules, involved in cell structure and mitosis.
- Enzymes accelerate chemical reactions without altering the final equilibrium by lowering the activation energy. Proteins have an active site for substrate binding and product formation.
- Proteins are composed of amino acids linked by peptide bonds.
- Amino acid side chains have varying shapes, sizes, charges, and polarities, defining protein properties.
Protein Structure Levels
Primary Structure
- The linear sequence of amino acids defines the protein's structure.
- The sequence is determined by the gene's sequence (3 DNA bases = 1 amino acid).
- Amino acids are linked by peptide bonds.
- Proteins usually consist of 50 to 2000 amino acids but can be longer. Shorter chains are called peptides.
- Rotation is restricted around peptide bonds.
Secondary Structure
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Folding of the polypeptide chain into regular structures stabilised by hydrogen bonds.
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Denatured proteins are unstable chains that fold into stable native conformations.
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Some proteins self-fold, others require chaperones.
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α-helix: Hydrogen bonds between amino and carboxyl groups of amino acids 4 residues apart.
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β-sheet: Hydrogen bonds between amino and carboxyl groups further apart and across different strands.
Tertiary Structure
- The overall 3D structure of the protein.
- Stabilised by non-covalent interactions between side chains (hydrophobic, hydrophilic, electrostatic, van der Waals forces).
- Hydrophobic interactions drive the folding of the polypeptide chain with hydrophobic amino acids buried in the interior.
- Disulfide bridges form covalent cross-links between cysteine residues.
Quaternary Structure
- Formed by the assembly of multiple polypeptide subunits.
- Examples include dimers, trimers, and tetramers (e.g., haemoglobin).
Post-Translational Modifications
- Modifications of proteins after synthesis, like:
- Methylation: Adding methyl groups (reversible).
- Glycosylation: Adding sugars (reversible), especially on secreted proteins.
- Ubiquitination: Attaching ubiquitin, marking for degradation (irreversible).
- Phosphorylation: Adding phosphate groups (reversible) by kinases, regulating enzyme functions.
Protein Targeting
- Proteins are directed to specific cellular locations.
- Signal sequences direct proteins to particular organelles.
- Some proteins are completely synthesized in the cytoplasm and then delivered to the specific location via the secretory pathway.
- Membrane proteins can span the membrane (hydrophobic regions inside, hydrophilic regions outside).
Membrane Anchoring
- Some proteins are anchored to membranes by hydrophobic groups attached to their sequences.
DNA as the Genetic Material
Mendelian Laws of Inheritance
- Segregation: Genes occur in pairs and individuals pass one to offspring.
- Independent assortment: Different genes are inherited independently.
- Dominance: Dominant allele masks recessive.
Transforming Principle
- Griffith’s experiment demonstrated a transforming principle, a heritable substance passed between bacteria.
- Avery, MacLeod, and McCarty identified DNA as the transforming principle, through various experiments (e.g., enzyme digestions).
Bacteriophage Genetic Material
- Hershey-Chase experiment demonstrated that DNA is the genetic material of bacteriophages:
- Labelled bacteriophage DNA or protein using radioactive isotopes.
- Injected into bacteria to track the label's location after phage multiplication.
- Identified DNA as the genetic material that enters the host cell.
DNA Structure
Chargaff's Rules
- Equal amounts of purines and pyrimidines. (A=T, G=C)
- Base composition varies between species, in terms of %A+T : %G+C.
Watson and Crick Model of DNA
- Double helix, antiparallel strands.
- A-T and G-C base pairing via hydrogen bonds.
- Right-handed helix, with major and minor grooves.
- One turn every 10.5 base pairs.
Chromosomes and Plasmids
- Chromosomes carry most genetic material.
- Eukaryotic chromosomes are linear, with packaging proteins (e.g., histones).
- Prokaryotic chromosomes are circular, with plasmids also circular, but smaller (often carrying advantageous genes such as antibiotic resistance).
- Telomeres protect chromosome ends.
DNA Binding Proteins
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DNA binding proteins regulate gene expression, cut DNA at specific sequences, and or protect DNA.
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Examples:
- Transcriptional regulators (e.g., lac repressor in the lac operon)
- Restriction endonucleases
- Histones (chromatin packaging in eukaryotes).
DNA Replication
Semiconservative Replication
- Meselson-Stahl experiment confirmed semiconservative DNA replication:
- Two strands of the original DNA molecule separate. Each of the two strands serve as templates for a new strand that is synthesized.
- Semi conservative involves DNA strands seperating into one old strand and one new strand.
DNA Replication Enzogenes
- Primase: Generates RNA primers.
- DNA polymerase: Adds nucleotides in 5' to 3' direction.
- DNA ligase: Joins Okazaki fragments.
- Topoisomerase: Relieves torsional stress.
- Helicase: Unwinds DNA at replication forks.
- Single-strand binding proteins: Prevent re-annealing of DNA strands.
Leading and Lagging Strands
- Leading strand: Synthesized continuously.
- Lagging strand: Synthesized discontinuously in Okazaki fragments.
Telomeres
- Telomeres protect chromosome ends from erosion during replication.
- Telomerase replenishes telomeres in some cells.
Studying That Suits You
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Description
Test your knowledge on the essential concepts of protein structure and function. This quiz covers everything from the basic building blocks of proteins, their diverse roles in biological processes, to the intricate levels of protein structure. Perfect for students of biology looking to reinforce their understanding of proteins.
