Comprehensive Study Guide for Cells, Cellular Transport, and Genetics

Foundational Cell Theory and Biological Components

• The Three Pillars of Cell Theory: The cell theory is a fundamental principle in biology which establishes that:

  • All living organisms are composed of one or more cells.

  • Cell processes and life functions occur within the boundaries of the cell.

  • All cells originate from pre-existing living cells of the same kind.

• Criteria for Living Organisms: To be classified as a living organism, an entity must possess specific capabilities:

  • The ability to nourish itself.

  • The capacity for growth.

  • The ability to reproduce.

• The Chemical Basis of Life: Carbon is the central element for living things due to its unique atomic structure:

  • It has the ability to form four covalent bonds with other atoms, allowing for the construction of complex biological molecules.

  • Carbon atoms have four valence electrons in their outer shell.

• Macromolecules and Metabolism:

  • Carbohydrates: Complex carbohydrates are polymers that break down into monomers known as simple sugars (monosaccharides).

  • Proteins: Specific proteins known as enzymes act as biological catalysts to speed up chemical reactions within the cell.

Cell Structures and Comparison

• Organelles of Eukaryotic Cells:

  • Nucleus: The defining organelle of eukaryotic cells that contains the genetic information (DNA).

  • Mitochondrion: The site where cellular respiration occurs; it is characterized by having a double membrane structure.

  • Chloroplast: The plant-specific organelle responsible for photosynthesis.

  • Ribosomes: Structures involved in protein synthesis.

  • Endoplasmic Reticulum: A network involved in the transport and synthesis of proteins and lipids.

  • Nucleolus: Located inside the nucleus, involved in ribosome production.

• Distinctive Structures in Plant vs. Animal Cells:

  • Shared Structures: Both plant and animal cells contain mitochondria for cellular respiration.

  • Plant-Specific Structures: Plant cells possess a cell wall (for protection and structural support) and plastids, such as chloroplasts.

  • Animal-Specific Structures: Animal cells utilize centrioles during the process of mitosis.

• Prokaryotic vs. Eukaryotic Cells:

  • Prokaryotic Cells: These cells lack a true nucleus and do not contain membrane-bound organelles. They are typically smaller than eukaryotic cells.

  • Eukaryotic Cells: These cells possess a true nucleus enclosed by a nuclear membrane and contain various membrane-bound organelles.

Cellular Energetics: Respiration and Photosynthesis

• Cellular Respiration: This process occurs in the mitochondria and releases three primary products:

  • Carbon dioxide ($CO_2$).

  • Water ($H_2O$).

  • Energy (in the form of ATP).

• Photosynthesis: This process occurs in the chloroplasts of plant cells.

  • Necessary Inputs: Plants require water ($H_2O$), carbon dioxide ($CO_2$), and sunlight (radiant energy) to perform photosynthesis.

• Energy Carrier Molecules: The chemical energy supply for all living cells is stored in specific molecules:

  • ATP (Adenosine Triphosphate): The primary energy currency of the cell. When a phosphate bond is broken, energy is released for muscle contraction, photosynthesis, and locomotion.

  • ADP (Adenosine Diphosphate): The molecule formed when ATP releases energy; it can be recharged back into ATP.

Cellular Transport Mechanisms

• Passive Transport: The movement of substances across the cell membrane without the expenditure of cellular energy.

  • Osmosis: A specific type of passive transport involving the movement of water.

• Solution Tonicity and the Cell Membrane:

  • Hypotonic Solution: A solution where the concentration of solutes is lower outside the cell than inside. This causes more water to move into the cell than out, potentially causing the cell to swell.

  • Hypertonic Solution: A solution where the concentration of solutes is higher outside the cell than inside, causing water to leave the cell.

  • Isotonic Solution: A solution where the concentration of solutes is equal inside and outside the cell, resulting in no net movement of water.

  • Permeability: The property of the membrane that allows certain substances to pass through.

• Active Transport: The movement of substances into or out of a cell that requires the use of energy (ATP).

  • Endocytosis: The process of bringing materials into the cell using energy.

  • Exocytosis: The process of expelling materials from the cell using energy.

DNA Structure, Replication, and Protein Synthesis

• DNA Replication: This process ensures that genetic information is copied. It occurs during the Interphase of the cell cycle.

• DNA Sequencing and Complementary Strands: DNA bases pair specifically (Adenine with Thymine, Cytosine with Guanine).

  • Example: If a DNA sequence is CCTAGT, the correct complementary DNA strand is GGATCA.

• Transcription: The process by which mRNA makes a copy of a portion of the DNA strand.

  • Mechanism: RNA uses Uracil (U) instead of Thymine (T).

  • Example Transition: A DNA chain of A-G-C-T-T-A-G-C-G-C-A-T-A-A-C transcribes into the mRNA chain U-C-G-A-A-U-C-G-C-G-U-A-U-U-G.

• Translation: The process occurring at the ribosome where the cell uses information from mRNA to produce proteins with the assistance of tRNA (transfer RNA).

  • mRNA (Messenger RNA): Transports the genetic code from the DNA in the nucleus to the ribosome in the cytoplasm.

Cell Division: Mitosis and Meiosis

• Mitosis: Cell division occuring in somatic cells (body cells).

  • Purpose: Growth and repair of tissues.

  • Outcome: Generates two daughter cells that are genetically identical to the mother cell.

  • Metaphase: The specific stage where chromosomes line up on spindles in the center of the cell.

• Meiosis: A specialized type of cell division necessary for sexual reproduction.

  • Outcome: Results in the formation of gametes (reproductive cells).

  • Crossing Over: The process in which homologous chromosomes exchange pieces of DNA during meiosis, increasing genetic diversity.

  • Non-disjunction: An error where chromosomes fail to separate properly during meiosis, often resulting in chromosomal mutations or fetal disorders.

• Mutations:

  • Frame Shift Mutation: A mutation caused by the addition or deletion of a single base in the DNA sequence, altering the reading frame.

  • Point Mutation: A change in a single nucleotide base.

Principles of Genetics and Heredity

• Mendelian Principles:

  • Inheritance: Traits are inherited through the passing of "factors" (genes) from parents to offspring.

  • Principle of Dominance: Some forms of a gene (alleles) can mask the expression of other forms.

• Genotype vs. Phenotype:

  • Genotype: The genetic makeup (e.g., $BB, Bb, bb$).

  • Phenotype: The observable physical characteristics (e.g., looking at a cat to determine its appearance).

• Genetic Crosses and Probability:

  • Monohybrid Cross (Heterozygous mice): Crossing a heterozygous female ($Bb$) with a heterozygous male ($Bb$) results in a genotypic ratio of $1:2:1$ ($1\,BB : 2\,Bb : 1\,bb$) and a phenotypic ratio of $3:1$ (Brown:White).

  • Freckle Inheritance: A homozygous dominant mother ($FF$) and a heterozygous father ($Ff$) have a $0\%$ chance of having a child who is homozygous recessive ($ff$).

• Non-Mendelian Inheritance:

  • Incomplete Dominance: Occurs when a cross between two different phenotypes produces a third, blended phenotype (e.g., a red flower and white flower producing pink offspring).

• Human Genetics and Tools:

  • Karyotyping: A visual map of an individual's chromosomes. The sex of a person is determined by chromosome pair 23.

  • Pedigree Charts: Used to track the inheritance of traits through generations. For an autosomal recessive disorder like sickle-cell anemia, affected individuals must have the homozygous recessive genotype ($aa$).

  • Amniocentesis: A medical detection method using a needle to sample amniotic fluid from around a fetus to check for genetic disorders.

  • Recessive Inheritance: A child can inherit a rare genetic disorder even if neither parent has the disease if both parents are asymptomatic carriers of the recessive allele.

Dihybrid Cross Analysis (Pea Plants)

• Trait Keys:

  • $G$ = Green (Dominant)

  • $g$ = Yellow (Recessive)

  • $I$ = Inflated (Dominant)

  • $i$ = Constricted (Recessive)

• Punnett Square Observations:

  • A box labeled with genotypes such as $GgIi$ represents a phenotype that is Green and Inflated.

  • A box labeled with genotypes such as $ggIi$ represents a phenotype that is Yellow and Inflated.

  • Genotype Example: If box 2 is the result of gametes $Gi$ and $GI$, the resulting genotype is $GGIi$.