Cell Biology: Signaling and Structure

Definition: Mechanisms by which cells communicate with each other, initiating cellular responses.
Components:
- Ligands: Signaling molecules (e.g., hormones, neurotransmitters).
- Receptors: Proteins on cell surfaces that bind ligands.
- Intracellular signaling molecules: Translate signals into cellular responses.
Types of Signaling:
- Autocrine: Cells respond to signals they secrete.
- Paracrine: Signals affect nearby cells.
- Endocrine: Hormones travel through the bloodstream to distant cells.
- Juxtacrine: Direct cell-to-cell contact for signaling.
Examples:
- MAPK/ERK pathway: Involved in cell proliferation.
- PI3K/Akt pathway: Regulates cell survival and metabolism.

Prokaryotic Cells:
- Lack a nucleus and membrane-bound organelles.
- Typically smaller and simpler (e.g., bacteria).
- Contain ribosomes, a cell membrane, and genetic material (DNA/RNA).
Eukaryotic Cells:
- Have a nucleus and membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).
- Generally larger and more complex (e.g., plant and animal cells).
- Organelles play specific roles in cellular functions.
Key Structures:
- Plasma Membrane: Semi-permeable barrier; regulates entry/exit of substances.
- Nucleus: Contains genetic material; site of transcription.
- Ribosomes: Protein synthesis.
- Mitochondria: Energy production through ATP.
- Endoplasmic Reticulum: Rough ER (protein synthesis) and Smooth ER (lipid synthesis).
- Golgi Apparatus: Modifies, sorts, and packages proteins.

Definition: Study of the structure and function of genes at a molecular level.
DNA Structure:
- Double helix composed of nucleotides (A, T, C, G).
- Base pairing: A-T and C-G.
Key Concepts:
- Chromosomes: DNA organized into structures containing genes.
- Gene: A segment of DNA that encodes a protein or functional RNA.
- Mutations: Changes in DNA sequence affecting function.
- Genetic Regulation: Mechanisms controlling gene expression and function.

Process:
1. Transcription: DNA is transcribed to mRNA in the nucleus.
2. Translation: mRNA is translated into a protein at ribosomes in the cytoplasm.
Key Players:
- mRNA: Carries genetic information from DNA.
- tRNA: Transfers amino acids to ribosomes during translation.
- Ribosomes: Sites of protein synthesis, consist of rRNA and proteins.
Stages of Translation:
- Initiation: Ribosome assembles around the mRNA.
- Elongation: Amino acids are added one by one to the growing polypeptide.
- Termination: Process ends when a stop codon is reached.

Definition: The process by which information from a gene is used to synthesize a functional gene product (usually proteins).
Regulation:
- Involves transcription factors that promote or inhibit transcription.
- Can occur at various levels: transcriptional, post-transcriptional, translational, and post-translational.
Mechanisms:
- Chromatin Remodeling: Modifies structure to allow or restrict access to DNA.
- RNA Processing: Involves splicing, capping, and polyadenylation of mRNA.
- Feedback Loops: Regulatory proteins can enhance or repress expression based on cellular conditions.
Epigenetics: Study of heritable changes in gene function that do not involve changes to the DNA sequence.

Cells communicate through signaling pathways that involve ligands binding to receptors on cell surfaces.
These pathways use intracellular signaling molecules to translate signals into cellular responses.
Types of signaling include autocrine (cells signal themselves), paracrine (cells signal nearby cells), endocrine (hormones travel through the bloodstream), and juxtacrine (direct cell-to-cell contact).
Examples of signaling pathways include the MAPK/ERK pathway, which is involved in cell proliferation, and the PI3K/Akt pathway, which regulates cell survival and metabolism.

Prokaryotic cells lack a nucleus and membrane-bound organelles, are typically smaller and simpler than eukaryotic cells.
Eukaryotic cells have a nucleus and membrane-bound organelles, are generally larger and more complex, and their organelles play specific roles in cellular functions.
Key structures in eukaryotic cells include the plasma membrane (regulates entry/exit of substances), nucleus (contains genetic material), ribosomes (protein synthesis), mitochondria (energy production), endoplasmic reticulum (protein and lipid synthesis), and Golgi apparatus (protein modification and packaging).

The study of genes at a molecular level involves understanding DNA structure and its function.
DNA is a double helix composed of nucleotides (adenine, thymine, cytosine, guanine), with base pairing rules: adenine with thymine, cytosine with guanine.
Important concepts include chromosomes (organized structures containing genes), genes (segments of DNA encoding proteins or functional RNA), mutations (changes in DNA sequence), and genetic regulation (mechanisms controlling gene expression and function).

The process involves transcription and translation.
Transcription occurs in the nucleus, where DNA is transcribed into mRNA.
Translation occurs at ribosomes in the cytoplasm, where mRNA is translated into a protein.
Key players include mRNA (carries genetic information), tRNA (transfers amino acids), and ribosomes (sites of protein synthesis).
Stages of translation include initiation (ribosome assembly around mRNA), elongation (addition of amino acids), and termination (stop codon recognition).

The process of using genetic information to synthesize functional gene products, primarily proteins.
Regulation involves transcription factors that promote or inhibit transcription.
Mechanisms include chromatin remodeling (modifies DNA accessibility), RNA processing (splicing, capping, polyadenylation), feedback loops (regulatory proteins based on cellular conditions), and epigenetics (heritable changes in gene function without DNA sequence changes).