Anatomy of a Chromosome

Anatomy of a Chromosome

• An unreplicated chromosome is referred to simply as a chromosome.
• A replicated chromosome remains classified as a chromosome.
• The two identical halves of a replicated chromosome are called sister chromatids.
• The centromere is the pinched center of a chromosome.
• The kinetochore, a protein complex around the centromere, attaches to the mitotic spindle during mitosis.

Telomeres

• Telomeres are protective DNA sequences located at the ends of chromosomes, preventing shortening.
• Human chromosomes are linear, exposing free DNA ends to nucleases that can degrade them.
• Telomeres "cap" chromosome ends to safeguard against nucleolytic degradation and are added by telomerase.
• One aging hypothesis suggests that telomeres shorten over time, leading to cell death when they reach a critical length.
• Lifestyle choices like smoking and obesity are linked to shortened telomeres.
• Cancer cells often exhibit overactive telomerase, which prolongs telomeres and promotes rapid cell division, contributing to tumor growth.

Mitosis

• Mitosis produces two identical diploid daughter cells.

Reproductive Cell Division

• Fertilization poses a challenge where an egg and sperm fuse; both having a full chromosome set would double the DNA.
• Gametes (eggs and sperm) must have half the DNA, achieved through meiosis.
• Meiosis involves two consecutive divisions and starts with diploid reproductive cells.

Meiosis I

• During Meiosis I, homologous chromosomes are segregated.
• Crossing over occurs early in Meiosis I, allowing genetic recombination between homologous chromosomes.
• Homologous chromosomes align at the equatorial plate during meiosis.
• The meiotic spindle partitions homologous chromosomes into two nonidentical daughter cells, each with a haploid set of chromosomes.

Meiosis II

• No DNA replication occurs between Meiosis I and Meiosis II.
• Meiosis II involves the segregation of sister chromatids.
• Replicated chromosomes align along the equatorial plate in Meiosis II.
• The meiotic spindle partitions sister chromatids into separate daughter cells, resulting in four nonidentical daughter cells, each with a haploid chromosome set.

Functional Groups of Organic Compounds

• Hydroxyl (R-O-H)

  • Characterizes alcohols
  • Provides a polar group, contributing to hydrophilicity in various compounds

• Sulfhydryl (R-S-H)

  • Integral to thiols, including amino acids like cysteine and methionine
  • Exhibits polarity and contributes to hydrophilicity

• Carbonyl

  • Part of ketones (structure on the left) and aldehydes (structure on the right)
  • Exhibits polar characteristics and is hydrophilic

• Carboxyl

  • Found in carboxylic acids and amino acids
  • At physiological pH, carboxyl groups carry a negative charge, enhancing hydrophilicity

• Ester

  • Common in dietary fats, oils, and triglycerides
  • Some medications, including aspirin, are classified as esters

• Phosphate

  • Essential part of ATP and nucleic acids
  • Negatively charged and exhibits strong hydrophilicity

• Amino

  • Key component of amino acids
  • At body pH, most amino groups are positively charged, contributing to hydrophilicity

Functional Groups of Organic Compounds

• Hydroxyl (R-O-H)

  • Characterizes alcohols
  • Provides a polar group, contributing to hydrophilicity in various compounds

• Sulfhydryl (R-S-H)

  • Integral to thiols, including amino acids like cysteine and methionine
  • Exhibits polarity and contributes to hydrophilicity

• Carbonyl

  • Part of ketones (structure on the left) and aldehydes (structure on the right)
  • Exhibits polar characteristics and is hydrophilic

• Carboxyl

  • Found in carboxylic acids and amino acids
  • At physiological pH, carboxyl groups carry a negative charge, enhancing hydrophilicity

• Ester

  • Common in dietary fats, oils, and triglycerides
  • Some medications, including aspirin, are classified as esters

• Phosphate

  • Essential part of ATP and nucleic acids
  • Negatively charged and exhibits strong hydrophilicity

• Amino

  • Key component of amino acids
  • At body pH, most amino groups are positively charged, contributing to hydrophilicity

This quiz delves into the structure and components of chromosomes, including unreplicated and replicated forms. It covers essential terms such as sister chromatids, centromeres, kinetochores, and telomeres. Test your understanding of these fundamental concepts in cell biology!