DNA Replication, Chromosomes, and Cell Division

• Cell transport mechanisms, reproduction, cell division (mitosis and meiosis), and genetics and DNA are key concepts in cell biology.

Active Transport

• Moves molecules against the concentration gradient, from low to high concentration.
• Requires energy in the form of ATP.
• Involves protein pumps, such as the sodium-potassium pump.

Passive Transport

• Doesn't require energy.
• Simple diffusion enables molecules to move directly through the membrane from high to low concentration.
• Facilitated diffusion uses protein channels to move molecules from high to low concentration.
• Osmosis refers to the diffusion of water through a membrane.

Endocytosis & Exocytosis

• Endocytosis involves the cell engulfing material.
• Exocytosis involves the cell expelling material

Asexual Reproduction

• Involves one parent, producing genetically identical offspring (clones).
• Advantages include speed and not needing a mate.
• Disadvantages include a lack of genetic diversity and vulnerability to disease.
• Examples include bacteria, plants, and some animals.

Sexual Reproduction

• Involves two parents and produces genetically unique offspring.
• Requires gametes (sperm and egg) that form a zygote.
• Advantages include genetic variation and better adaptation.
• Disadvantages include it needing time, energy, and a mate.

Mitosis

• Cell division that produces 2 identical diploid daughter cells.
• Occurs in somatic cells (body cells).
• Interphase precedes mitosis, involving cell growth, DNA replication, and preparation for division, including G1, S, and G2 phases.
• M Phase includes mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).
• Prophase involves chromosomes condensing.
• Metaphase involves chromosomes aligning at the cell center.
• Anaphase involves chromatids separating and moving to opposite sides.
• Telophase involves nuclear envelopes reforming around chromosomes.

Meiosis

• Occurs in germ cells (sperm and egg).
• Reduces chromosome number by half, from diploid to haploid.
• Creates genetic variation through crossing over and independent assortment.
• Meiosis I separates homologous chromosomes, reducing chromosome number.
• Meiosis II separates sister chromatids, similar to mitosis.
• The result is 4 unique haploid cells (sperm or egg)

DNA Structure

• Includes nucleotides: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
• A pairs with T, and C pairs with G.
• DNA forms a double helix structure

DNA Replication

• Occurs during the S phase of Interphase before cell division.
• Enzymes unzip the DNA and add complementary nucleotides to form two identical strands.

Chromosomes

• Humans have 46 chromosomes (23 pairs).
• Diploid cells have 2 sets of chromosomes (2n = 46).
• Gametes are haploid (1n = 23).
• Karyotype refers to a visual representation of chromosomes.

Key Terms

• Gametes are reproductive cells (sperm and egg).
• Zygote is a fertilized egg formed from sperm and egg.
• Diploid (2n) cells have two sets of chromosomes (46 chromosomes in humans).
• Haploid (1n) cells have one set of chromosomes (23 chromosomes in gametes).
• Homologous chromosomes have the same size and shape, carrying the same genes but possibly different alleles.

Important Concepts

• DNA replication ensures that daughter cells get an identical copy of DNA during mitosis.
• Mitosis results in 2 identical diploid cells.
• Meiosis results in 4 unique haploid cells and is important for genetic diversity.
• Some cells (like muscle and brain cells) do not divide but carry out normal functions in the G0 phase.

Question Answers

• For growth and repair, multicellular organisms undergo mitosis.
• The three stages of interphase are G1, S, and G2:
  • G1: cell grows for DNA replication
  • S: cells are replicated
  • G2: cell further grows for mitosis
• G0 is a place for going through normal functions without active prepping for cell division or dividing.
• The stages of mitosis in order are Prophase, Metaphase, Anaphase, and Telophase.
• Chromosomes line up in the middle of the cell during Metaphase.
• Asexual reproduction involves one parent, while sexual reproduction involves two.
• An advantage of asexual reproduction is speed, and a disadvantage is the lack of genetic diversity.
• An example of an organism that reproduces asexually is bacteria.
• The purpose of meiosis is to produce gametes for sexual reproduction.
• There are 46 chromosomes in a human somatic cell.
• There are 23 chromosomes in a human gamete.
• In the human body, gametes are produced in the testes in males and the ovaries in females.
• The daughter cells of meiosis are genetically different from the original parent cell and have half the number of chromosomes.
• Diploid refers to cells with two sets of chromosomes (2n), while haploid refers to cells with one set of chromosomes (1n).
• Chromosomes determine biological sex (XX for female, XY for male).
• DNA is a type of nucleic acid macromolecule
• The three components of a nucleotide are a sugar, a phosphate group, and a nitrogenous base.
• If a DNA strand is 20% Adenine (A), then 30% of the strand is Cytosine (C)
• DNA replication being semiconservative means each new DNA molecule contains one original strand and one newly synthesized strand.
• The complementary base-pairing rules are A with T and C with G.
• The "backbone" of the DNA molecule is made up of sugar and phosphate groups.
• If one DNA strand has the sequence TACGGC, the complementary strand is ATGCCG.

Multiple Choice Answers

• C: a duplicated chromosome failed to separate (nondisjunction)
• C: nucleotides
• D: thymine
• D: phosphate group
• D: chromosomes
• A: thymine
• A: carbon, hydrogen, oxygen, nitrogen, and phosphorus
• D: half as many
• A: nitrogenous bases
• B: deoxyribose, thymine, and a phosphate group
• A: A-G-C-T-T-A
• D: Each half of the original DNA molecule is joined with a new complementary DNA strand
• C: A strand of DNA containing genetic information.

Explore fundamental concepts of DNA replication, including strand separation and nucleotide composition. Understand chromosome structure, transport mechanisms, and the stages of the cell cycle. Review meiosis, mitosis, and chromosome number in diploid cells.