Cell Communication and Signaling (Chapter 11)

Types of Cell Signaling

Cells communicate through various signaling mechanisms, each suited to different distances and contexts.

• Cell-cell contact-dependent signaling: Direct interaction between membrane-bound molecules on adjacent cells.

• Paracrine signaling: Local signaling where cells release signals that affect nearby cells.

• Synaptic signaling: Specialized form of paracrine signaling in neurons; neurotransmitters cross synapses.

• Endocrine/hormonal signaling: Long-distance signaling via hormones released into the bloodstream.

Types of Signal Receptors

Signal receptors are proteins that detect and respond to signaling molecules.

• Receptor Tyrosine Kinases (RTKs): Membrane receptors that, upon ligand binding, dimerize and autophosphorylate, activating downstream signaling.

• G Protein Coupled Receptors (GPCRs): Membrane receptors that activate G proteins upon ligand binding, which then trigger intracellular responses.

• Ligand-activated channels: Ion channels that open in response to ligand binding, allowing ions to flow across the membrane.

Order of Steps:

• Ligand binds receptor.

• Receptor undergoes conformational change.

• Signal transduction cascade is initiated.

• Cellular response occurs.

Kinases vs. Phosphatases

• Kinase: Enzyme that adds phosphate groups to proteins (phosphorylation).

• Phosphatase: Enzyme that removes phosphate groups from proteins (dephosphorylation).

Target Cells and Signal Specificity

• Only cells with the appropriate receptor for a signal are "target cells" and can respond.

Second Messengers: cAMP and Ca2+

• cAMP: Produced from ATP by the enzyme adenylyl cyclase.

• Ca2+: Released from the endoplasmic reticulum (ER) into the cytosol via IP3-gated channels.

• Other second messengers: Inositol triphosphate (IP3) and diacylglycerol (DAG), produced from phospholipids by phospholipase C.

Apoptosis in C. elegans

• Programmed cell death is regulated by specific genes and signaling pathways.

• Ensures proper development and removal of damaged cells.

The Cell Cycle and Cell Division (Chapter 12)

Diploid and Haploid Numbers

• Diploid (2n): Two sets of chromosomes; in humans, 2n = 46.

• Haploid (n): One set of chromosomes; in humans, n = 23.

• Somatic cells: Diploid; contain both sets.

• Gametes: Haploid; contain one set.

Phases of the Cell Cycle

• G1 phase: Cell growth.

• S phase: DNA replication occurs.

• G2 phase: Preparation for mitosis.

• M phase: Mitosis and cytokinesis.

• After S phase, each chromosome consists of two sister chromatids.

Cytoskeletal Components in Cell Division

• Microtubules: Form the mitotic spindle, separating chromosomes.

• Microfilaments/Actin filaments: Form the contractile ring during cytokinesis in animal cells.

First Signs of Cytokinesis

• Animal cells: Formation of cleavage furrow.

• Plant cells: Formation of cell plate.

Cell Cycle Checkpoints

• G1 checkpoint: Checks for cell size, nutrients, and DNA integrity.

• G2 checkpoint: Ensures DNA replication is complete and undamaged.

• M checkpoint: Ensures chromosomes are properly attached to spindle before division.

Cancer Cells and Checkpoints

• Cancer cells often bypass checkpoints, leading to uncontrolled division.

Meiosis and Sexual Life Cycles (Chapter 13)

Homologous Chromosomes vs. Sister Chromatids

• Homologous chromosomes: Pair of chromosomes, one from each parent, with similar genes but possibly different alleles.

• Sister chromatids: Identical copies of a chromosome, joined after DNA replication.

Karyotype

• Visual representation of all chromosomes in a cell, arranged by size and shape.

Mitosis vs. Meiosis

• Goal of mitosis: Produce two identical diploid cells for growth and repair.

• Goal of meiosis I: Separate homologous chromosomes, reducing chromosome number by half.

• Goal of meiosis II: Separate sister chromatids, similar to mitosis.

• Unique to meiosis: Crossing over, independent assortment, reduction division.

• Shared events: Chromosome alignment, separation, cytokinesis.

• Mitosis is similar to meiosis II: Both involve separation of sister chromatids.

Independent Assortment

• Occurs during metaphase I of meiosis.

• Homologous chromosomes align randomly, creating genetic variation.

Mendelian Genetics (Chapter 14)

Dominant and Recessive Traits

• Dominant trait: Expressed when at least one dominant allele is present.

• Recessive trait: Expressed only when both alleles are recessive.

Key Vocabulary

• Homozygote: Individual with two identical alleles for a gene.

• Heterozygote: Individual with two different alleles for a gene.

• True breeding: Organism that always passes down the same trait.

• Allele: Variant form of a gene.

• Monohybrid/dihybrid: Crosses involving one or two traits, respectively.

• Self-cross: Crossing an organism with itself.

• Testcross: Crossing with a homozygous recessive to determine genotype.

• P/F1/F2 generations: Parental, first filial, and second filial generations.

• Phenotype: Observable traits.

• Genotype: Genetic makeup.

• Phenotypic ratio: Ratio of observable traits in offspring.

• Genotypic ratio: Ratio of genetic combinations in offspring.

Mendel's Experiments

• Monohybrid cross: True-breeding purple x white flowers; F1 all purple, F2 ratio 3:1 purple:white.

• Dihybrid cross: True-breeding yellow, round seeds x green, wrinkled seeds; F2 ratio 9:3:3:1.

Deduction of Parental Genotypes from Progeny Ratios

• 1:1 ratio: Parents are Aa x aa.

• 3:1 ratio: Parents are Aa x Aa.

Punnett Squares

• Used to predict genotypic and phenotypic ratios.

Independent Assortment

• Traits are inherited independently if genes are on different chromosomes.

Probability in Genetics

• Multiplication rule: Probability of two independent events both occurring:

• Addition rule: Probability of either event occurring:

Table: Comparison of Mitosis and Meiosis

Example: Using Punnett Squares

• For a monohybrid cross Aa x Aa:

• Punnett square yields genotypic ratio 1 AA : 2 Aa : 1 aa, phenotypic ratio 3 dominant : 1 recessive.

Additional info: Probability rules and Punnett squares are fundamental tools for predicting genetic outcomes and understanding inheritance patterns.