4.1 Life Cycle of the Cell

• What role does the DNA-genetic system play in cell reproduction?

  It controls all life processes.
• How do genes influence cell growth and division?

  They determine growth characteristics and division timing.
• What is the significance of the DNA-genetic system in human development?

  It controls each stage from fertilized ovum to body.
• What is the life cycle of a cell?

  The period from one reproduction to the next.
• How long can the life cycle of mammalian cells be?

  10 to 30 hours when reproducing rapidly.
• What event terminates the life cycle of a cell?

  A series of distinct physical events called mitosis.
• How long does the actual stage of mitosis last?

  About 30 minutes.
• What does interphase represent in the life cycle of a cell?

  More than 95 percent of the life cycle.
• What typically affects the life cycle of a cell?

  Inhibitory factors that slow or stop reproduction.
• What is the life cycle period for highly stimulated bone marrow cells?

  As little as 10 hours.
• How long can the life cycle of most nerve cells last?

  An entire lifetime of the human body.
• Where does cell reproduction begin?

  In the nucleus.
• What is the first step in cell reproduction?

  Replication of all DNA in the chromosomes.
• When does DNA duplication begin before mitosis?

  5 to 10 hours before mitosis.
• How long does DNA duplication take to complete?

  4 to 8 hours.
• What is the result of DNA replication?

  Two exact replicas of all DNA.
• What do the replicas become in daughter cells after DNA replication?

  The DNA in the two new daughter cells
• How long is the period before mitosis begins after DNA replication?

  1 to 2 hours
• What begins to happen during the period before mitosis?

  Preliminary changes for mitosis occur
• What are the key differences between DNA replication and RNA transcription?

  • Both DNA strands are replicated
  • Entire strands are replicated end to end
  • DNA polymerase is the principal enzyme
  • DNA ligase bonds successive nucleotides
• What is the principal enzyme for replicating DNA?

  DNA polymerase
• What does DNA ligase do during DNA replication?

  It bonds successive DNA nucleotides
• How are new DNA strands formed during replication?

  Simultaneously in hundreds of segments
• How do newly formed DNA strands remain attached to the original strand?

  By loose hydrogen bonding
• Why is uncoiling of DNA helixes necessary?

  To prevent entanglement during replication
• What mechanism helps uncoil the DNA helixes?

  Enzymes that cut and resplice the helix
• What is the process of correcting inappropriate DNA nucleotides called?

  DNA proofreading
• What happens when a mistake is made during DNA replication?

  It is called a mutation
• What can mutations lead to in cells?

  Abnormal protein formation and cell death
• How many mutations might occur from one human generation to another?

  10 or more mutations
• How is the human genome represented to protect against mutations?

  By two separate sets of chromosomes
• What is the approximate length of DNA helixes in each chromosome?

  6 centimeters
• What is the role of DNA polymerases in DNA repair?

  They replace defective nucleotides
• What is the consequence of a mutation in the genome?

  Formation of abnormal proteins
• How does the presence of two sets of chromosomes benefit a child?

  Provides a functional gene despite mutations