Cell Structure, Function, and Cellular Processes in Anatomy & Physiology

Introduction to the Human Body

Overview

The study of Anatomy & Physiology explores the structure and function of the human body, focusing on how cells, tissues, and organs work together to sustain life. Understanding the cell as the basic unit of life is foundational to this field.

• Anatomy: The study of body structure.

• Physiology: The study of body function.

• Cells are the building blocks of all living things and carry out all chemical activities needed to sustain life.

Chemistry and the Human Body

Key Concepts

• All living organisms are composed of chemical elements and compounds.

• Biochemical reactions are essential for cellular processes such as energy production, growth, and repair.

• Cellular respiration is a central process that converts energy from food into ATP, the energy currency of the cell.

Cells: Structure and Function

General Structure of the Cell

Cells share general structures but are specialized for different functions. They are organized into three main regions:

• Plasma membrane: The outer boundary of the cell.

• Nucleus: The control center containing genetic material.

• Cytoplasm: The fluid and organelles between the plasma membrane and nucleus.

Plasma Membrane

• Composed of a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins.

• Phospholipids have hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails, forming a selective barrier.

• Integral proteins span the membrane and assist in transport; peripheral proteins are attached to the membrane surface.

• Selective permeability: The membrane allows some substances to pass while excluding others.

Nucleus

• Surrounded by a nuclear envelope with pores for material exchange.

• Contains the nucleolus (site of ribosome production) and chromatin (DNA and protein).

Cytoplasm and Organelles

• Cytosol: Fluid suspending organelles.

• Inclusions: Stored nutrients or cell products.

• Organelles: Specialized structures performing specific functions.

Major Organelles and Their Functions

Organelle	Structure	Function
Rough Endoplasmic Reticulum (RER)	Membranous, studded with ribosomes	Protein synthesis and membrane production
Smooth Endoplasmic Reticulum (SER)	Membranous, no ribosomes	Lipid synthesis, detoxification, metabolism
Ribosomes	Protein and RNA, free or attached	Sites of protein synthesis
Golgi Apparatus	Stack of membranes	Modifies, packages, and ships proteins
Lysosomes	Membranous sacs with enzymes	Digest non-usable materials (cellular 'garbage disposal')
Peroxisomes	Membranous sacs with enzymes	Detoxify harmful substances
Mitochondria	Double membrane, inner folds (cristae)	ATP production via cellular respiration
Cytoskeleton	Network of protein filaments	Structural support, cell movement
Centrioles	Microtubule pairs	Cell division (mitotic spindle formation)
Cilia/Flagella	Microtubule-based projections	Movement of cell or materials across surface

Cell Transport Processes

Overview

Cells regulate the movement of substances across their membranes using passive and active transport mechanisms.

Passive Transport

• Does not require energy

• Types include:

  • Simple diffusion: Movement of solutes from high to low concentration.

  • Osmosis: Diffusion of water across a membrane.

  • Facilitated diffusion: Movement via protein channels or carriers.

  • Filtration: Movement due to pressure gradient.

Active Transport

• Requires cellular energy (ATP)

• Types include:

  • Solute pumping: Protein carriers move substances against concentration gradients.

  • Bulk transport: Movement of large quantities via vesicles.

    • Exocytosis: Vesicles fuse with membrane to release contents outside the cell.

    • Endocytosis: Cell engulfs material into vesicles (includes phagocytosis for solids and pinocytosis for liquids).

Cell Cycle and Division

Phases of the Cell Cycle

• Interphase: Cell grows, functions, and replicates DNA.

• Cell Division: Includes mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Mitosis Stages

1. Prophase: Chromatin condenses, spindle forms, nuclear envelope dissolves.

2. Metaphase: Chromosomes align at the cell equator.

3. Anaphase: Sister chromatids separate to opposite poles.

4. Telophase: Nuclear envelopes reform, chromosomes decondense.

Cytokinesis follows, splitting the cytoplasm and forming two identical daughter cells.

Mnemonic: PMAT (Prophase, Metaphase, Anaphase, Telophase)

Protein Synthesis

Overview

Protein synthesis is the process by which cells build proteins based on genetic instructions. It involves two main phases:

1. Transcription: DNA is used as a template to make messenger RNA (mRNA) in the nucleus.

2. Translation: mRNA is decoded by ribosomes in the cytoplasm to assemble amino acids into a protein.

Key Terms

• Gene: A sequence of DNA that codes for a protein.

• Codon: A sequence of three nucleotides on mRNA that specifies an amino acid.

• Anticodon: A complementary three-nucleotide sequence on tRNA.

• RNA types: mRNA (messenger), tRNA (transfer), rRNA (ribosomal).

Summary Table: DNA vs. RNA

Feature	DNA	RNA
Strands	Double	Single
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G

Cellular Respiration

Overview

Cellular respiration is the process by which cells convert energy from food (mainly glucose) into ATP. It occurs in three main stages:

1. Glycolysis: Occurs in the cytoplasm; glucose is split into two pyruvic acid molecules, producing ATP and NADH.

2. Krebs Cycle (Citric Acid Cycle): Occurs in mitochondria; pyruvic acid is broken down, producing ATP, NADH, and FADH2.

3. Electron Transport Chain (ETC): Occurs in mitochondria; electrons from NADH and FADH2 generate a large amount of ATP.

Total ATP yield: 36 or 38 ATP per glucose molecule (depending on cell type and shuttle systems).

Summary Table: Stages of Cellular Respiration

Stage	Location	Main Products
Glycolysis	Cytoplasm	2 ATP, 2 NADH, 2 Pyruvate
Krebs Cycle	Mitochondrial matrix	2 ATP, 6 NADH, 2 FADH2
Electron Transport Chain	Inner mitochondrial membrane	32-34 ATP, H2O

Aerobic vs. Anaerobic Respiration

• Aerobic respiration: Requires oxygen; produces high ATP yield.

• Anaerobic respiration: Occurs without oxygen; produces lactic acid and much less ATP (e.g., in muscle cells during intense exercise).

Genetic and Epigenetic Regulation

Genetic Regulation

• Gene expression is controlled at multiple levels, including transcription and translation.

• Transcription factors and regulatory sequences determine which genes are active.

Epigenetic Regulation

• Epigenetics involves changes in gene expression without altering the DNA sequence.

• Mechanisms include DNA methylation and histone modification.

• Epigenetic changes can be influenced by environment and can be reversible.

Comparison: Transcription vs. Translation

Process	Location	Function
Transcription	Nucleus	DNA to mRNA
Translation	Cytoplasm (ribosome)	mRNA to protein

Additional info: These notes synthesize and expand upon the provided material, filling in standard academic context for clarity and completeness.