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Questions and Answers

What carries hereditary information?

Chromosomes

Which bases form 2 hydrogen bonds?

  • A and C
  • A and T (correct)
  • C and G
  • G and T
  • Which bases are purines?

  • A and G (correct)
  • C and T
  • A and T
  • C and G
  • The sequence of nucleotides in a gene determines the amino acid sequence in a protein.

    <p>True</p> Signup and view all the answers

    What is the primary structure formed by DNA?

    <p>Double helix</p> Signup and view all the answers

    What are transposable elements?

    <p>Mobile pieces of DNA</p> Signup and view all the answers

    Which of the following structures protect the ends of chromosomes?

    <p>Telomeres</p> Signup and view all the answers

    The noncoding regions inside a gene are called ______ and the coding regions are called ______.

    <p>introns, exons</p> Signup and view all the answers

    What is the primary function of regulatory DNA sequences?

    <p>To control gene expression</p> Signup and view all the answers

    All human chromosomes are identical.

    <p>False</p> Signup and view all the answers

    Match the following structures with their functions:

    <p>Centromere = Allows sister chromatids to be pulled into daughter cells Telomeres = Protects the ends of chromosomes Replication origin = Location where bi-directional duplication begins Karyotype = Display of chromosomes during mitosis</p> Signup and view all the answers

    Study Notes

    Genes and Heredity

    • Genes hold instructions defining species traits.
    • Hereditary information is encoded on chromosomes.
    • Chromosomes are composed of DNA and protein in equal amounts.
    • DNA strands run antiparallel with 5' phosphate and 3' hydroxyl ends.
    • Adenine (A) pairs with Thymine (T) through 2 hydrogen bonds.
    • Cytosine (C) pairs with Guanine (G) through 3 hydrogen bonds.
    • Purines (A & G) are larger with two rings, while pyrimidines (C & T) are smaller with one ring.
    • This base pairing ensures consistent width of DNA.
    • Phosphodiester bonds link sugars in DNA, connecting the phosphate group of one sugar to the hydroxyl group of the next.
    • DNA chains are linear and directional.
    • DNA's linear polymer structure, with 4 monomer types, provides a chemical basis for storing genetic information.
    • DNA's complementary strands act as templates for replication, ensuring information transmission across generations.
    • DNA encodes proteins, with genes containing instructions for protein production.
    • The linear sequence of nucleotides in a gene dictates the linear sequence of amino acids in a protein, forming the genetic code.
    • The genome encompasses the entire set of RNA molecules and proteins an organism can produce.

    Nuclear Structure

    • The nuclear envelope consists of two concentric bilayer membranes, punctured by nuclear pores.
    • The outer nuclear membrane is continuous with the endoplasmic reticulum (ER).
    • The nuclear envelope is supported by the nuclear lamina.
    • Each chromosome contains a single long DNA molecule along with proteins that compact the DNA and RNA molecules essential for gene expression, DNA duplication, and repair.
    • Chromatin is a complex of DNA and tightly bound proteins.

    Chromosomes

    • Gametes, non-dividing cells, lack DNA or replicate without a complete cell cycle and lack homologous chromosomes.
    • Most human cells have two copies of each chromosome, termed homologous chromosomes.
    • Sex chromosomes are non-homologous.
    • DNA painting uses short nucleic acid sequences attached to colored probes that bind to complementary sequences on DNA, allowing for chromosome identification.
    • Chromosomes can be distinguished by staining them with dyes to create unique banding patterns reflecting chromatin structure and base composition.
    • A karyotype is a display of the 46 human chromosomes during mitosis.

    Genome Composition

    • The genome contains non-coding DNA alongside genes, some of which regulate gene expression.
    • Differences in non-coding DNA explain variations in genome size.
    • Non-coding DNA contributes significantly to genome size differences between closely related organisms despite similar gene numbers.
    • The specific arrangement of the genome into chromosomes varies across eukaryotic species.
    • Mobile DNA segments called transposable elements, which integrate into chromosomes over time, constitute half of the chromosomal DNA.
    • Introns are non-coding regions within genes, while exons represent coding regions.
    • Introns typically make up the majority of a gene.
    • Regulatory DNA sequences, scattered over vast nucleotide regions, control gene activation and deactivation.

    Cell Cycle and Chromosomal Structure

    • During interphase, the cell actively expresses genes, synthesizes proteins, and replicates DNA to produce sister chromatids.
    • The M phase occurs after DNA replication is complete.
    • During the M phase, the nucleus divides into two daughter nuclei, chromosomes condense, the nuclear envelope breaks down, the mitotic spindle forms, and a complete set of chromosomes is pulled apart by the mitotic spindle.
    • The nuclear envelope reforms around each set of chromosomes.
    • During interphase, chromatin exists in long threads.
    • Three specific DNA sites regulate replication and sister chromatid separation:
      • Replication Origin: The starting point of bidirectional DNA duplication. Eukaryotes have multiple origins to accelerate replication.

      • Centromere: Enables sister chromatids to move into daughter cells. Kinetochores form on centromeres and allow the mitotic spindle to pull sister chromatids apart.

      • Telomeres: Located at chromosome ends, these sequences facilitate the replication of chromosome termini and protect them from being misinterpreted as broken DNA.

    • In budding yeast, these sites are short.
    • While telomere sequences for eukaryotes are short, centromeres and replication origins are long and complex.
    • The specific sequence coding for centromeres is not well-defined.
    • Interphase chromosomes decondense and recondense to allow gene expression, DNA replication, and other processes.

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