Cell Structure, Protein Synthesis, and the Cell Cycle: Study Notes for Anatomy & Physiology

Cellular Energy and Organelles

ATP Production and Mitochondria

The cell's energy currency is ATP (adenosine triphosphate), which is produced primarily in the mitochondria. Mitochondria are often called the "powerhouses" of the cell due to their role in energy metabolism.

• ATP: A molecule that stores and transfers energy within cells.

• Mitochondria: Organelles that use oxygen (O2) to produce ATP through cellular respiration.

• Cellular Respiration Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

• Intermediate Filaments: Cytoskeletal structures that help distribute stress across the cell.

Additional info: Intermediate filaments provide mechanical support and help maintain cell integrity.

Protein Synthesis and Processing

Build, Remodel, Demolish: Protein Lifecycle

Cells constantly build, remodel, and degrade proteins to maintain function and respond to changing conditions.

• DNA to RNA: Transcription occurs in the nucleus, producing messenger RNA (mRNA).

• RNA to Protein: Translation occurs on ribosomes, synthesizing proteins from amino acids.

• Protein Remodeling: Proteins can be modified, folded, and transported to their destinations.

• Protein Degradation: Damaged or unneeded proteins are broken down, often by proteasomes or lysosomes.

Ribosomes and Endoplasmic Reticulum (ER)

Ribosomes are the sites of protein synthesis. They can be free in the cytoplasm or bound to the rough ER.

• Free Ribosomes: Synthesize proteins for use within the cell.

• Rough ER: Studded with ribosomes; synthesizes proteins destined for secretion or membrane insertion.

• Smooth ER: Lacks ribosomes; involved in lipid synthesis and calcium storage.

Protein Targeting and Modification

Proteins are directed to specific cellular locations and may be chemically modified for function.

• Signal Sequence: Short peptide that directs ribosome to the ER for membrane or secreted proteins.

• Golgi Apparatus: Modifies, sorts, and packages proteins for delivery.

• Vesicles: Membrane-bound sacs that transport proteins between organelles.

Genetic Code and mRNA

mRNA Structure and Translation

Messenger RNA (mRNA) carries genetic information from DNA to ribosomes for protein synthesis.

• Start Codon (AUG): Signals the beginning of translation.

• Stop Codons (UAA, UGA, UAG): Signal the end of translation.

• Codons: Triplets of nucleotides that specify amino acids.

Cell Cycle and Mitosis

Overview of the Cell Cycle

The cell cycle consists of phases that prepare the cell for division and ensure accurate DNA replication.

• Interphase: Period of growth and DNA synthesis.

• Mitotic Phase: Division of the nucleus and cytoplasm.

Interphase Subphases

• G1 Phase: Cell growth and protein synthesis.

• S Phase: DNA replication.

• G2 Phase: Preparation for mitosis.

Mitotic Phase: Steps of Mitosis

Mitosis is the process by which a cell divides its nucleus and distributes chromosomes to daughter cells.

1. Prophase: Chromosomes condense, spindle fibers form, nuclear envelope breaks down.

2. Metaphase: Chromosomes align at the cell's equator.

3. Anaphase: Sister chromatids are pulled apart to opposite poles.

4. Telophase/Cytokinesis: Nuclear envelopes reform, cytoplasm divides, two daughter cells are produced.

Chromosome Structure and Key Terms

• Centromere: Region where sister chromatids are attached.

• Kinetochore: Protein complex that links chromatids to spindle fibers.

• Telomere: Protective end region of chromosomes.

Table: Key Organelles and Their Functions

Organelle	Main Function	Additional Info
Mitochondria	ATP production via cellular respiration	Uses O2, produces CO2 and H2O
Rough ER	Protein synthesis for secretion/membrane	Studded with ribosomes
Smooth ER	Lipid synthesis, calcium storage	No ribosomes
Golgi Apparatus	Protein modification and packaging	Sorts proteins for delivery
Ribosome	Protein synthesis	Free or bound to ER

Summary

Understanding the structure and function of cellular organelles, the process of protein synthesis, and the stages of the cell cycle is essential for mastering Anatomy & Physiology. These processes ensure that cells grow, divide, and maintain homeostasis, which is fundamental to the health and function of all tissues and organs.