Cell Structure and Protein Synthesis
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Questions and Answers

What is the main function of the plasma membrane?

  • To synthesize proteins
  • To store genetic information
  • To produce energy for the cell
  • To regulate the movement of substances into and out of the cell (correct)

    • What type of molecule forms the hydrophobic center of the phospholipid bilayer?

  • Phosphates
  • Carbohydrates
  • Fatty acids (correct)
  • Proteins

    • Which of these is NOT a function of membrane proteins?

  • Transport of molecules
  • Energy production (correct)
  • Cell signaling
  • Structural support

    • What is the main role of histones in DNA packaging?

    <p>They interact with DNA's negative charge, enabling spooling. (B)</p> Signup and view all the answers

    Which form of chromatin is actively involved in transcription?

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

    Which of the following factors is NOT involved in the initiation stage of protein synthesis?

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

    During elongation, where does the next amino acid attach to the growing polypeptide chain?

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

    What is the role of a stop codon in protein synthesis?

    <p>To signal the end of translation (D)</p> Signup and view all the answers

    Which of the following is NOT a potential post-translational modification of a polypeptide chain?

    <p>Addition of a phosphate group (C)</p> Signup and view all the answers

    What is the main function of DNA?

    <p>To store and transmit genetic information (D)</p> Signup and view all the answers

    Which of these is NOT a known destination of proteins?

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

    What is the difference between a gene and a genome?

    <p>A gene is a segment of DNA that codes for a protein, while a genome is the complete set of genetic information in a cell. (B)</p> Signup and view all the answers

    What is the process of translating genetic information into a protein called?

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

    What is the relationship between a codon and an amino acid?

    <p>Multiple codons code for one amino acid (D)</p> Signup and view all the answers

    What is the role of tRNA in protein synthesis?

    <p>tRNA carries amino acids to the ribosome (A)</p> Signup and view all the answers

    Which of these is NOT a way that the proteome is more complex than the genome?

    <p>Proteins can be spliced together in different combinations after transcription. (B)</p> Signup and view all the answers

    Which of these is NOT a way in which protein synthesis can be regulated?

    <p>Regulation of the process of translation by ribosomes. (B)</p> Signup and view all the answers

    What is a common feature of proteins that will be directed to the endoplasmic reticulum, Golgi complex, secretory vesicles, plasma membrane, or lysosomes?

    <p>They have a signal sequence or leader sequence. (A)</p> Signup and view all the answers

    How can proteins be modified after translation?

    <p>All of the above. (D)</p> Signup and view all the answers

    What determines the final location of a protein within a cell?

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

    What is the role of a promoter in protein synthesis?

    <p>It signals the beginning of transcription. (C)</p> Signup and view all the answers

    What is the purpose of splicing in pre-mRNA processing?

    <p>To remove introns from the mRNA transcript. (B)</p> Signup and view all the answers

    What role do transcription factors play in protein synthesis?

    <p>They can activate or repress transcription. (A)</p> Signup and view all the answers

    What is the main function of RNA polymerase in transcription?

    <p>To unwind the DNA double helix and allow RNA nucleotides to bind to the template strand. (A)</p> Signup and view all the answers

    Which of the following is involved in the translation process? (Select all that apply)

    <p>mRNA (A), tRNA (B), Ribosomes (C)</p> Signup and view all the answers

    What is the role of the A site in a ribosome during translation?

    <p>It holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (C)</p> Signup and view all the answers

    What happens during the termination stage of transcription?

    <p>The RNA transcript is released from the DNA template. (B)</p> Signup and view all the answers

    Which of the following describes what may happen in RNA interference?

    <p>tRNA cannot bring amino acids to mRNA. (B)</p> Signup and view all the answers

    Flashcards

    Heterochromatin

    Inactive regions of DNA that are highly condensed.

    Gene

    A DNA sequence that codes for a specific amino acid sequence or RNA.

    Genome

    The total genetic information in the DNA of a typical cell.

    Transcription

    The process where DNA is copied to mRNA in the nucleus.

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    Codon

    A sequence of 3 nucleotides in mRNA that codes for an amino acid.

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    Plasma Membrane

    A selective barrier made of a phospholipid bilayer that regulates what enters and exits the cell.

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    Fluid-Mosaic Model

    A model describing the plasma membrane as a mix of various proteins floating in or on the fluid lipid bilayer.

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    Integral Proteins

    Transmembrane proteins that span across the plasma membrane, allowing selective transport of substances.

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    Euchromatin

    A form of DNA that is less tightly packed; active in transcription for gene expression.

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    Histones

    Positively charged proteins that package and spools DNA in the nucleus, aiding in structure.

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    Leader Sequence

    A short peptide that directs proteins to their proper locations.

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    Rough ER Role

    Translates and modifies proteins before sending them to the Golgi complex.

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    Proteome

    The complete set of proteins expressed in a cell at a certain time.

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    Posttranslational Modification

    Changes made to proteins after translation, affecting their function.

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    Regulation of Protein Synthesis

    Controlling transcription and translation processes to influence protein production.

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    Initiation of Translation

    The process where initiation factors assemble mRNA, ribosomal subunits, and initiator tRNA at the start codon.

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    Elongation in Translation

    The stage where tRNA brings amino acids to the ribosome, joining them into a polypeptide chain.

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    Termination of Translation

    The process where the ribosome reaches a stop codon and releases the completed polypeptide.

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    Chaperone Proteins

    Proteins that assist in folding nascent polypeptides into their proper tertiary and quaternary structures.

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    mRNA

    Messenger RNA carries genetic information from DNA to ribosomes for protein synthesis.

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    Promoter

    A DNA sequence that signals where transcription begins.

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    Exons and Introns

    Exons are coding sequences, while introns are non-coding portions of a gene.

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    Splicing

    The modification of pre-mRNA where introns are removed and exons are joined.

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    tRNA

    Transfer RNA carries specific amino acids to the ribosome during translation.

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    Ribosome

    A cellular structure where mRNA and tRNA interact to synthesize proteins.

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    Translation

    The process of synthesizing polypeptides from mRNA templates using ribosomes and tRNA.

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    Study Notes

    Cell Structure: Plasma Membrane and Protein Synthesis

    • Cells have a plasma membrane, a selective barrier.
    • Phospholipid bilayer forms the core forming a hydrophobic barrier
    • Phosphate heads interact with water.
    • Fatty acid tails are hydrophobic.
    • Proteins and phospholipids move laterally within the membrane.
    • Fluid mosaic model describes the dynamic nature.
    • Membrane proteins allow selective passage of substances.

    A Typical Cell Components

    • Nucleus: Contains DNA, controls cell activities.
    • Nucleolus: Site of ribosome production.
    • Rough endoplasmic reticulum (RER): Ribosomes attached, processes proteins.
    • Smooth endoplasmic reticulum (SER): Lacks ribosomes, synthesizes lipids.
    • Golgi apparatus: Modifies, sorts, and packages proteins.
    • Mitochondria: Powerhouse of the cell, produces ATP.
    • Lysosomes: Contain enzymes, break down waste.
    • Ribosomes: Responsible for protein synthesis.
    • Centrioles: Involved in cell division
    • Secretory vesicles: Transport molecules outside the cell.
    • Microtubules: Part of the cytoskeleton, maintain cell shape.

    DNA in the Nucleus

    • Chromatin: DNA is packaged with proteins (histones).
    • Histones: Positively charged proteins, interact with negatively charged DNA.
    • Euchromatin: Active in transcription, less condensed.
    • Heterochromatin: Inactive regions, highly condensed.

    Genetic Code & Protein Synthesis

    • DNA directs protein synthesis
    • Gene: DNA sequence coding for a protein or mRNA.
    • Genome: Total genetic information in a cell. Human genome ~25,000 genes.
    • DNA triplets (codons) code for specific amino acids.
    • Genetic code is universal.

    Basic Steps of Protein Synthesis

    • DNA is transcribed into mRNA in the nucleus.
    • mRNA moves to the cytoplasm.
    • mRNA is translated into protein by ribosomes.

    Protein Synthesis: Transcription

    • Transcription is DNA-directed RNA synthesis.
    • mRNA is synthesized from a DNA template.
    • mRNA carries the genetic code from DNA to the ribosomes.
    • Steps of transcription include initiation, elongation, and termination.
    • RNA polymerase binds to a promoter region in DNA.
    • Elongation involves addition of complementary RNA bases to the template strand.
    • Termination occurs at a stop codon.
    • Pre-mRNA needs modification before translation.

    Pre-mRNA modification

    • Removal of introns.
    • Addition of a 5' cap and a 3' poly-A tail.
    • Alternative splicing.
    • Splicing of introns to generate mature mRNA.

    RNA Interference

    • Some RNA molecules can block translation or destroy specific mRNA molecules
    • Silences genes, blocking protein synthesis.

    Protein Synthesis: Translation

    • Ribosomes are complex particles
    • mRNA binds to the ribosome.
    • tRNA brings amino acids to the ribosome.
    • Enzymes catalyze peptide bond formation between amino acids.
    • The polypeptide chain grows until the stop codon is reached.

    Ribosome

    • Complex structure made of two subunits (small and large).
    • Three sites for tRNA binding: A site, P site, E site.
    • Ribosomes are responsible for linking amino acids together to form polypeptide chains.

    Protein Synthesis: Translation Steps

    • Initiation: Initiation factors, small subunit, initiator tRNA, large subunit form complex at start codon.
    • Elongation: tRNA brings amino acids, peptidyl transferase links them, ribosome moves.
    • Termination: Stop codon, polypeptide released.

    Post-translational Modifications

    • Chaperones help proteins fold correctly.
    • Cleavage, addition of lipids or carbohydrates, methylation, phosphorylation.
    • Protein modification can affect protein functionality and destination.

    Destination of Proteins

    • Proteins are targeted to specific compartments within the cell.
    • Leader sequences direct protein's destination.
    • Proteins ending up in cytoplasm, organelles (mitochondria, etc), or secreted from the cell.
    • Proteins are transported throughout or out of the cell.
    • proteins travel using transport vesicles.

    Role of Rough ER in Protein Synthesis

    • Ribosomes on RER synthesize proteins.
    • Proteins enter RER lumen for processing.
    • RER directs protein processing, folding and transport.
    • Proteins can be packaged or become membrane proteins for insertion into the cellular membrane or transported outside of the cell.

    Proteome

    • Proteome refers to all proteins expressed by a cell or organism at a given time.
    • The proteome's composition is dynamic and regulated based on a variety of factors (environmental and internal).
    • Proteins can be modified
    • Post-translational modifications
    • Protein modification can impact protein function and fate.

    Major Regulation of Protein Synthesis

    • Transcriptional regulation.
    • Translational regulation
    • Factors affecting protein synthesis efficiency.

    Regulation of Protein Synthesis

    • Regulation of protein synthesis occurs at various points in the process.
    • Various mechanisms used to turn genes on and off, and enhance or limit protein synthesis as needed.

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    Related Documents

    Protein Synthesis Notes PDF

    Description

    This quiz covers key concepts related to cell structure, including the plasma membrane and various organelles involved in protein synthesis. Test your understanding of the fluid mosaic model, nucleus, endoplasmic reticulum, Golgi apparatus, and other cell components. Ideal for students studying cell biology or related subjects.

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