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Questions and Answers

What triggers the proteolytic degradation of reductase?

  • Increase in cellular concentrations of cholesterol (correct)
  • Activation of SREBP
  • Decrease in mevalonate levels
  • Phosphorylation by AMP-dependent kinase

What happens to SREBP when cholesterol levels fall?

  • It is degraded in the cytoplasm.
  • It is proteolytically processed and activated. (correct)
  • It is transported back to the ER.
  • It remains in the nucleus.

How does the proportion of protein in a lipoprotein affect its density?

  • More protein leads to decreased density.
  • More protein results in greater density. (correct)
  • All lipoproteins have uniform density levels.
  • Density is independent of protein content.

Which lipoprotein is responsible for scavenging excess cholesterol?

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

What is the main consequence of a defect in LDL receptors?

<p>Familial hypercholesterolemia and atherosclerosis. (B)</p> Signup and view all the answers

What characterizes the core of lipoprotein particles?

<p>Cholesterol esters and hydrophobic lipids. (B)</p> Signup and view all the answers

How does LDL enter peripheral tissues?

<p>Receptor-mediated endocytosis. (A)</p> Signup and view all the answers

What is the potential consequence of a point mutation?

<p>It can result in a silent, neutral, missense, or nonsense mutation. (D)</p> Signup and view all the answers

What happens to LDL after it is hydrolyzed in the cell?

<p>LDL receptors are recycled. (A)</p> Signup and view all the answers

How do somatic mutations differ from germline mutations?

<p>Somatic mutations do not affect future generations. (A)</p> Signup and view all the answers

What happens during insertion mutations?

<p>An extra nucleotide is added, causing a shift in the reading frame. (A)</p> Signup and view all the answers

Which type of mutation results in a premature stop codon?

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

How do DNA repair systems operate?

<p>They can introduce mutations due to their imprecision. (B)</p> Signup and view all the answers

Which statement about amino acid mutations is true?

<p>Mutations can be specific to an environmental adaptation. (D)</p> Signup and view all the answers

Which type of mutation only affects the nucleotide level?

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

What is the consequence of environmental stress on mutations?

<p>It may lead to the development of mutations that confer survival advantages. (B)</p> Signup and view all the answers

Which enzyme catalyzes the formation of 5-phosphoribosyl-1-amine from PRP and glutamine?

<p>Glutamine phosphoribosyl aminotransferase (C)</p> Signup and view all the answers

What is the final product of the purine pathway?

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

Which amino acid is added to IMP to form AMP?

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

Which of the following substances acts as a suicide inhibitor in nucleotide synthesis?

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

What is required for the conversion of ribonucleotide diphosphates to deoxyribonucleotides?

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

What important role does 5-phosphoribosyl-1-amine serve in purine metabolism?

<p>It is the initial compound in the purine synthesis pathway. (B)</p> Signup and view all the answers

Which nucleotide is formed when IMP is hydrated and oxidized?

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

Which compound provides a necessary carbon group for the synthesis of TMP from dUMP?

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

What role do human accelerated regions (HARs) mainly play in the human genome?

<p>They act as regulatory elements. (C)</p> Signup and view all the answers

How do nuclear hormone receptors regulate transcription after binding with their ligand?

<p>They recruit proteins that enhance transcription. (D)</p> Signup and view all the answers

Which domain of nuclear hormone receptors is responsible for binding to DNA?

<p>Zinc finger domain (A)</p> Signup and view all the answers

What effect does histone acylation have on DNA?

<p>It neutralizes the polarity of histones. (A)</p> Signup and view all the answers

What process involves cutting and splicing RNA after transcription?

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

Which statement is true about the function of RNA polymerase I?

<p>It synthesizes ribosomal RNA precursors. (B)</p> Signup and view all the answers

What happens to some receptors in their unbound state?

<p>They bind to repressors and inhibit transcription. (C)</p> Signup and view all the answers

What initiates the release of repressors from nuclear hormone receptors?

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

What distinguishes TAGs from glycerophospholipids?

<p>TAGs have a 3rd fatty acyl. (B)</p> Signup and view all the answers

Which compound is commonly formed as a precursor in the synthesis of phospholipids?

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

How is phosphatidate activated in the synthesis pathway?

<p>By reacting it with CTP. (D)</p> Signup and view all the answers

Which head group is the most abundant in phosphatidylcholine?

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

What occurs during phosphatidylcholine synthesis when there is a deficiency of choline?

<p>It will be synthesized by methylating phosphatidylthanolamine. (B)</p> Signup and view all the answers

Which of the following statement is true regarding dietary choline requirements?

<p>They increase with pregnancy. (C)</p> Signup and view all the answers

What drives the activation of serine or inositol in the phospholipid synthesis pathway?

<p>PP hydrolysis. (A)</p> Signup and view all the answers

What role does excess cholesterol play in the metabolization of food energy substrates?

<p>It is converted into acetyl-CoA. (C)</p> Signup and view all the answers

What is the role of GTP in the formation of the 70s complex?

<p>It facilitates the binding of the 50s subunit to the initiation complex. (C)</p> Signup and view all the answers

During prokaryotic elongation, what is the function of elongation factor?

<p>It moves the mRNA by one codon using ATP hydrolysis. (C)</p> Signup and view all the answers

What distinguishes eukaryotic translation from prokaryotic translation?

<p>Eukaryotic ribosomes are larger and synthesize in the nucleus. (B)</p> Signup and view all the answers

Why do stop codons in prokaryotes require release factors (RF)?

<p>They facilitate the release of tRNA and the newly synthesized protein from the ribosome. (C)</p> Signup and view all the answers

What is the first amino acid incorporated during eukaryotic protein synthesis?

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

What occurs when the ribosomal complex encounters a stop codon?

<p>Release factors bind and promote disassociation of tRNA and mRNA from the complex. (A)</p> Signup and view all the answers

What is an essential feature of eukaryotic mRNA that helps in translation?

<p>It is circular to facilitate protein interactions with the poly-A tail. (D)</p> Signup and view all the answers

Which of the following is NOT a characteristic of prokaryotic genes?

<p>They undergo extensive processing before translation. (B)</p> Signup and view all the answers

Flashcards

Fatty acid role in complex lipids

Fatty acids are components of complex lipids like triglycerides (TAGs) and glycerophospholipids.

Triglyceride structure

Triglycerides have a glycerol backbone and three fatty acyl chains.

Glycerophospholipid structure

Glycerophospholipids consist of a glycerol backbone, two fatty acyl chains, and a polar head group.

Phosphatidate formation

Phosphatidate is a precursor formed by adding a fatty acyl to a glycerol-3-phosphate molecule.

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Phospholipid head group

A polar head group is important to phospholipid structure, for example serine, inositol, choline, or ethanolamine.

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Phosphatidate activation

Phosphatidate is activated by CTP, forming a CDP intermediate, which is driven by PP hydrolysis.

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Phosphatidylcholine synthesis

Abundant phospholipid synthesized from choline or through methylation of phosphatidylthanolamine when dietary choline is low.

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Dietary Choline Importance

Dietary choline requirements are increased during pregnancy. Sufficient dietary choline is required for phosphatidylcholine synthesis.

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SREBP function

SREBP is a transcription factor that regulates the synthesis of cholesterol biosynthesis enzymes when cholesterol levels are low.

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SREBP activation

SREBP, initially in the ER, is proteolytically processed and activated in the Golgi complex, moving to the nucleus to initiate cholesterol biosynthesis.

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Cholesterol regulation

High cholesterol levels decrease reductase activity, and low levels activate it, which SREBP drives.

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Lipoprotein structure

Lipoproteins are spherical particles with a phospholipid monolayer exterior, proteins inside to dissolve lipids, and hydrophobic core lipids, including cholesterol esters.

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Lipoprotein density

Lipoprotein density is inversely related to the proportion of protein: more protein, greater density.

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LDL function

LDL delivers cholesterol to peripheral tissues.

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LDL receptor

LDL receptor facilitates cholesterol uptake in cells via endocytosis, and, after use, receptors are recycled.

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Familial Hypercholesterolemia

A genetic condition marked by deficient LDL receptors, causing cholesterol accumulation in the blood.

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Point Mutation

A single nucleotide change in DNA sequence. It can lead to a silent, neutral, missense, or nonsense mutation.

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Silent Mutation

A point mutation that does not change the amino acid sequence of the encoded protein.

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Missense Mutation

A point mutation that alters the amino acid sequence of the encoded protein.

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Nonsense Mutation

A point mutation that introduces a premature stop codon.

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Insertion Mutation

The addition of one or more nucleotides into the DNA sequence.

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Somatic Mutations

Mutations that occur in non-reproductive cells, affecting only the individual. Not passed to offspring.

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Germline Mutations

Mutations that occur in reproductive cells, passed on to offspring.

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DNA Repair Systems

Cellular mechanisms that identify and correct errors in DNA sequences, preventing mutations.

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Purine Synthesis

The process of creating purine bases, adenine and guanine, which are essential components of DNA and RNA.

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IMP: The Starting Point

Inosine monophosphate (IMP) is the final product of the purine pathway. AMP and GMP are derived from IMP.

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AMP Formation

Adenosine monophosphate (AMP) is formed from IMP in a pathway requiring GTP.

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GMP Formation

Guanosine monophosphate (GMP) is formed from IMP in a pathway requiring ATP.

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Deoxyribonucleotide Synthesis

Deoxyribonucleotides, the building blocks of DNA, are made from ribonucleotide diphosphates via a reduction reaction.

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TMP Formation

Thymine monophosphate (TMP) is formed from dUMP by methylation using a carbon group from folate.

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Inhibiting Nucleotide Synthesis

Blocking nucleotide synthesis can hinder cell growth, a key principle in chemotherapy.

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Fluorouracil: Suicide Inhibitor

Fluorouracil is a dUMP analog that acts as a suicide inhibitor, preventing the formation of TMP.

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What are Human Accelerated Regions (HARs)?

HARs are specific segments of the human genome that have undergone rapid evolution compared to chimpanzees. They are conserved across most vertebrates but show significant variations in humans.

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Where are HARs located?

Most HARs reside within introns, which are non-coding regions within genes. They are often found near protein-coding genes, suggesting a role in regulating protein synthesis and gene expression.

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What are response elements?

Response elements are specific DNA sequences that bind to transcription factors. They are activated by various stimuli, regulating gene expression in response to factors like hormones, growth factors, and environmental changes.

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What are transcription factors?

Transcription factors are proteins that bind to DNA and regulate the transcription of genes. They act as 'on/off' switches for gene expression.

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What are the domains of nuclear hormone receptors?

Nuclear hormone receptors possess four key domains: 1) Aminoterminal activation domain, 2) Zinc finger DNA-binding domain, 3) Hinge domain, and 4) Ligand-binding domain.

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How do nuclear hormone receptors regulate transcription?

Nuclear hormone receptors can either activate or suppress transcription. They bind to co-activators to stimulate gene expression or to co-repressors to inhibit gene expression.

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What is histone acetylation?

Histone acetylation is a process where acetyl groups are added to lysine residues on histones. This neutralizes the histone's charge, weakening its grip on DNA and allowing for easier gene expression.

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How is RNA modified after transcription?

After transcription, RNA undergoes various modifications like cutting, splicing, insertion, deletion, and substitution of nucleotides. These changes influence gene expression depending on cell type or developmental stage.

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Prokaryotic Translation Initiation

The process of assembling the ribosome, mRNA, and initiator tRNA to begin protein synthesis in prokaryotic cells. It involves the formation of the 30S initiation complex, followed by the binding of the 50S subunit to form the 70S ribosome.

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Initiation Factors (IFs)

Proteins that facilitate the assembly of the initiation complex during translation. They help align the mRNA, initiator tRNA, and ribosomal subunits, and then detach after the complex is formed.

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Formylmethionine (fMet)

The modified methionine residue that is the first amino acid incorporated into a prokaryotic protein. It is recognized by the initiator tRNA and binds to the start codon (AUG) on the mRNA.

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Elongation in Prokaryotes

The repetitive process where amino acids are added to the growing polypeptide chain. It involves the delivery of aminoacyl-tRNAs to the A site of the ribosome, peptide bond formation, and translocation of the mRNA to the next codon.

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Translocation

The movement of the ribosome along the mRNA in a 5' to 3' direction, shifting the polypeptide chain from the A site to the P site and leaving the A site vacant for the next tRNA.

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Stop Codons

Three specific codons (UAA, UAG, UGA) that signal the termination of translation. They are not recognized by any tRNA, but by release factors.

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Release Factors (RFs)

Proteins that bind to the stop codon in the A site of the ribosome, causing the release of the completed polypeptide chain and dissociation of the ribosome from the mRNA.

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Eukaryotic Translation

Protein synthesis in eukaryotic cells shares similarities with prokaryotic translation, but with key differences.

  • Ribosomes are larger (80S) and initiation involves more protein factors.
  • First amino acid is methionine (not formylmethionine).
  • Initiation codon is always the first AUG from 5' end of mRNA.
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Study Notes

Chapter 29 Notes

  • Fatty acids are often subcomponents of complex lipids, like glycerophospholipids, which have a glycerol backbone and two fatty acyl chains.
  • Phospholipids have a head group, and phosphatidate is a common precursor, formed from DHAP and phosphorylated glycerol.
  • Phosphatidylcholine is the most abundant phospholipid in mammals, and its synthesis is influenced by dietary choline.
  • If choline stores are adequate, phosphatidylcholine will be synthesized by methylating phosphatidylethanolamine.
  • Cholesterol synthesis is primarily in the liver, though other tissues can also synthesize it.
  • The pathway involves several stages: stage one is converting excess food/energy into acetyl-CoA, which gets converted to cholesterol and energy. Stage two and three occur in the endoplasmic reticulum, making isopentenyl phosphate, starting with 3 acetyl-CoA.

Chapter 30 Notes

  • Amino acids are formed from the digestion of proteins and from the breakdown of defective or excess proteins.
  • Aminotransferases transfer amino groups to a-ketoglutarate, forming glutamate, and releasing pyruvate, and other related intermediates
  • The urea cycle converts ammonia into urea for excretion.
  • This cyclical process occurs primarily in the liver in humans.
  • It is catalyzed by carbamoyl phosphate synthetase (CPSI) and requires two ATP, and is an irreversible reaction.
  • The final step of the urea cycle cleaves arginine into urea and ornithine catalysed by arginase
  • Aromatic amino acids are both ketogenic and glucogenic
  • Phenylketonuria (PKU) is a genetic disorder where phenylalanine is not degraded properly and results in the accumulation of phenylalanine and related metabolites in the body.
  • Elevated phenylalanine levels disrupt brain growth and metabolism, which causes phenylpyruvate to be excreted in the urine.

Chapter 32 Notes

  • Nucleotides are composed of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and a phosphate group.
  • Nucleotides can be mono-, di-, or tri-phosphate.
  • Nucleotides can be synthesized de novo (from scratch) or via salvage pathways.
  • The purine synthesis pathway produces IMP, which gets further processed into AMP and GMP.
  • The pyrimidine synthesis pathway produces UMP, which can be further modified to form other pyrimidine nucleotides.
  • Deoxyribonucleotides are formed from ribonucleotides via reduction.

Chapter 33 Notes

  • Mutations are changes in nucleotide sequence.
  • Mutations can be classified as point mutations (single nucleotide changes) or large-scale mutations (e.g., deletions, duplications, inversions).
  • Point mutations can be synonymous (no change in amino acid), neutral (minor change in amino acid), missense (change to a different amino acid), or nonsense (change to a stop codon).
  • Large-scale mutations can cause significant changes in the resulting protein.
  • Genetic screening of newborns can detect individuals with conditions like phenylketonuria (PKU).

Chapter 34 Notes

  • DNA replication is a semiconservative process, where each new DNA molecule contains one original strand and one newly synthesized strand.
  • DNA polymerase needs a 3'-OH group to add nucleotides (5' → 3' direction).
  • Enzymes like topoisomerases help in unwinding and restoring supercoils during replication.
  • Leading strands are synthesized continuously, while Okazaki fragments are synthesized discontinuously on lagging strands.
  • Topoisomerases are responsible for resolving supercoiling during DNA replication.
  • Both prokaryotic and eukaryotic DNA polymerases have exonuclease activity to correct replication errors and remove mismatches.
  • Telomeres are repetitive DNA sequences at chromosome ends that protect against degradation.

Chapter 35 Notes

  • Point mutations are single nucleotide changes in the DNA sequence and can result in silent mutations, neutral mutations, missense mutations, or nonsense mutations.
  • Large-scale mutations are changes affecting larger segments of the chromosome, including insertions, deletions, duplications, and inversions.
  • Synonymous mutations do not affect the amino acid sequence.
  • Nonsynonymous mutations change the amino acid sequence.
  • Large-scale mutations can lead to significant phenotypic changes, including genetic diseases.

Chapters 36 and 37 Notes

  • RNA is synthesized from a DNA template by RNA polymerase, which is sensitive to α-amanitin.
  • RNA polymerase I synthesizes rRNA; RNA polymerase II synthesizes mRNA precursors (pre-mRNA); and RNA polymerase III synthesizes tRNA.
  • Eukaryotic mRNA undergoes extensive processing, including 5' capping, 3' polyadenylation, and splicing of introns.
  • Transcription factors bind to promoter regions to regulate the initiation of transcription.
  • Enhancers and response elements influence the strength of transcription.

Chapter 38 Notes

  • RNA polymerase I, II, and III synthesize rRNA, mRNA precursors, and tRNA, respectively, and are sensitive to different inhibitors.
  • RNA processing involves 5' capping, 3' polyadenylation, and splicing of introns in pre-mRNA.
  • Alternative splicing creates multiple mRNAs from a single gene, increasing proteomic diversity.

Chapter 39 Notes

  • The genetic code is a triplet code where each three-nucleotide codon specifies a particular amino acid.
  • The genetic code is degenerate, meaning multiple codons can specify the same amino acid.
  • Transfer RNA (tRNA) molecules are adaptor molecules that carry amino acids to the ribosome.
  • tRNA molecules have an anticodon that base-pairs with the mRNA codon.
  • Aminoacyl-tRNA synthetase is an enzyme that attaches the correct amino acid to its corresponding tRNA.

Chapter 40 Notes

  • Translation is the process of protein synthesis, where ribosomes read mRNA to synthesize proteins.
  • Ribosomes have three binding sites: A site, P site, and E site.
  • Initiation factors (IFs) and elongation factors (EFs) are needed for the initiation and elongation steps of translation.
  • Termination factors (RFs) are needed to terminate translation.

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