Cell Structure and Function

• Cells represent the fundamental structural and functional units of life.
• Cell biology focuses on the study of cell structure and function.
• The cell theory comprises that all living organisms consist of cells, cells constitute the basic structural and functional units in living organisms, and new cells arise from pre-existing cells.

Two Main Types of Cells

• Prokaryotic cells are characterized by the absence of a nucleus and other membrane-bound organelles.
• Bacteria and Archaea are categorized as prokaryotic cells.
• Eukaryotic cells possess a nucleus and various membrane-bound organelles.
• Protists, fungi, plants, and animals are classified as eukaryotic cells.

Prokaryotic Cell Structure

• A plasma membrane encloses the cell.
• The cytoplasm occupies the region within the plasma membrane.
• DNA resides in the cytoplasm without a defined nucleus.
• Ribosomes facilitate protein synthesis.
• A cell wall offers structural support and protection.
• Certain prokaryotes feature a capsule exterior to the cell wall.
• Pili assist in attachment.
• Flagella enable movement.

Eukaryotic Cell Structure

• The plasma membrane bounds the cell.
• The cytoplasm fills the area inside the plasma membrane.
• The nucleus houses the cell's DNA.
• Organelles are membrane-bound structures performing specialized functions.
• Ribosomes are responsible for protein synthesis.
• The endoplasmic reticulum (ER) participates in protein and lipid synthesis.
• The Golgi apparatus manages protein processing and packaging.
• Lysosomes contain enzymes for degrading cellular waste.
• Mitochondria generate energy via cellular respiration.
• Chloroplasts (in plant cells) conduct photosynthesis.
• The cytoskeleton imparts structure and support.
• Plant cells include a cell wall.

Plasma Membrane

• The plasma membrane is a selectively permeable barrier that separates the cell's interior from its external environment.
• It consists of a phospholipid bilayer with embedded proteins and other molecules.
• Phospholipids feature a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.
• Proteins within the plasma membrane facilitate transport, signaling, and cell recognition.

Nucleus

• The nucleus houses the cell's DNA, arranged into chromosomes.
• It is enclosed by a nuclear envelope containing pores for transport.
• The nucleolus is the site of ribosome synthesis.

Ribosomes

• Ribosomes are in charge of protein synthesis.
• They are present in the cytoplasm and on the rough endoplasmic reticulum.

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is a network of membranes that participates in protein and lipid synthesis.
• Rough ER has ribosomes attached and is involved in protein synthesis and modification.
• Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.

Golgi Apparatus

• The Golgi apparatus handles the processing and packaging of proteins and lipids
• This includes modifying, sorting, and directing proteins to their final destinations.

Lysosomes

• Lysosomes house enzymes that break down cellular waste and debris.
• They participate in autophagy (self-eating) and apoptosis (programmed cell death).

Mitochondria

• Mitochondria create energy using cellular respiration
• A double membrane structure characterizes them.

Chloroplasts

• Chloroplasts reside in plant cells and algae.
• They perform photosynthesis, which transforms light energy into chemical energy.
• Their structure includes a double membrane, and they contain chlorophyll.

Cytoskeleton

• The cytoskeleton composes a grid of protein fibers to support the cell
• It supports cell movement and division, as well as the transportation of materials.
• Microfilaments, intermediate filaments, and microtubules are its main components.

Cell Wall

• Cell walls are present in plant cells, bacteria, fungi, and algae.
• It provides support and protection.
• Plant cell walls consist of cellulose.

Cell Size

• Most cells can only be seen with a microscope.
• Cell size is restricted by the surface area-to-volume ratio.
• As cells enlarge, volume increases more quickly than surface area.
• A high surface area-to-volume ratio is essential for effective material exchange with the environment.

Cell Organization

• Cells arrange to form tissues.
• Tissues organize to form organs.
• Organs assemble into organ systems.
• Organ systems function together to form an organism.

Cell Communication

• Cells communicate through chemical signals, which can occur locally or over long distances.
• Cell signaling happens in three stages: reception, transduction, and response.

Cell Division

• Growth, repair, and reproduction depend on cell division.
• Prokaryotic cells undergo binary fission for division.
• Eukaryotic cells use mitosis or meiosis to divide.
• Mitosis creates two identical daughter cells.
• Meiosis produces four genetically different daughter cells, each possessing half the parental chromosome number.

Cellular Respiration

• Cells use cellular respiration to convert glucose into ATP, an energy-carrying molecule.
• This happens in the mitochondria.
• It consists of glycolysis, the Krebs cycle, and the electron transport chain stages.

Photosynthesis

• During photosynthesis, plants and algae transform light energy into chemical energy.
• The chloroplasts are where it takes place.
• Light-dependent reactions and the Calvin cycle are involved.

Cell Specialization

• Through differentiation, cells mature to conduct specific tasks
• Differentiation causes cells to acquire unique traits.
• Gene expression defines a cells function through controlling protein production.

Cell Junctions

• Cell junctions link cells.
• Tight junctions stop extracellular fluid leakage.
• Adherens junctions and desmosomes create robust connections.
• Gap junctions enable cell-to-cell communication.