Cell Structure and Types

• A cell is the fundamental unit of life, possessing a highly organized structure that carries out vital functions.
• Cell components work together to maintain cellular homeostasis and perform essential life activities.

Types of cells

• Prokaryotic cells lack a defined nucleus.
• Eukaryotic cells have a defined nucleus.
• Prokaryotic cells have dispersed genetic material in the cytoplasm.
• Plant cells have a cellulose cell wall, chloroplasts, and vacuoles and are multicellular.
• Animal cells have no cell wall and are multicellular.
• Protists can have a cell wall, without differentiated tissues.
• Fungi have a chitin cell wall and are heterotrophs.

Cell Size and Microscopy

• A microscope is needed to examine most cells.
• 1 centimeter (cm) = 1/100 of a meter.
• 1 millimeter (mm) = 1/1000 of a meter.
• 1 micrometre (1 μ) = 1/1,000,000 of a meter.
• 1 nanometre = 1/1,000,000,000 of a meter.

Basic Cell Structures

• All cells have a plasma/cell membrane and cytoplasm.
• Eukaryotes contain a nucleus, while prokaryotes have a nucleoid region instead.
• Prokaryotes do not have membrane-bound organelles.

Nucleus

• A membrane-bound organelle that houses deoxyribonucleic acid (DNA) and stores genetic information.
• It is usually located near the center of eukaryotic cells.
• Controls cell function.
• DNA is transcribed to RNA (ribonucleic acid,) needed for protein synthesis and cellular processes
• Replication of DNA (deoxyribonucleic acid) for cell division
• Contains the nucleolus, which is involved in ribosome synthesis.
• The nuclear envelope is a membrane with pores that allow materials to move in and out.

Nucleoid

• Prokaryotes do not have a true nucleus.
• DNA aggregates into a distinct structure.
• DNA is transcribed to RNA (ribonucleic acid) for protein synthesis and cellular processes.
• Replication of DNA (deoxyribonucleic acid) for cell division.
• Genome size is significantly smaller than in eukaryotes.

Cytoplasm

• Occupies the space inside the plasma membrane (intracellular space.)
• In eukaryotes, it is outside the nucleus, contains the cytosol, organelles, and cytoskeleton.
• The cytosol contains a gel-like fluid that contains water, salts, proteins, and other molecules
• the organelles contain little organs and a cytoskeleton
• The cytoplasm plays a crucial role in biochemical reactions, energy production, substance transport and cellular metabolism.

Protein Synthesis

• Building and repairing cellular structures.
• Regulating biological processes.
• Expressing specific characteristics of each organism are all due to proteins.

Ribosomes

• Essential organelles for cellular functioning and survival.
• Consist of two separate RNA-protein complexes known as the small and large subunit.
• They synthesize proteins by bonding amino acids together, using messenger RNA (mRNA) as a sequence template.
• Ribosomes are located in the cytoplasm and the rough endoplasmic reticulum (in eukaryotes).

Endoplasmic Reticulum (ER)

• A network of interconnected membranes that extends from the nuclear membrane to the cell membrane.
• Plays a fundamental role in the transport, processing, and distribution of proteins and lipids within the cell.
• Rough Endoplasmic Reticulum is studded with ribosomes and is involved in the synthesis and modification of proteins.
• Smooth Endoplasmic Reticulum specializes in lipid synthesis, carbohydrate metabolism, calcium storage, and detoxification.

Golgi Apparatus

• Key in the processing and packaging of proteins and lipids produced in the endoplasmic reticulum (into secretory vesicles).
• Synthesizes carbohydrates and lipoproteins and is essential for maintaining the cell's internal balance and facilitating communication with the outside.
• Composed of a series of flattened sacs called cisternae and acts as the 'shipping center' of the cell, sorting and packaging proteins into vesicles for transport and distribution.

Energy Supply

• Carries out vital functions and necessary metabolic processes, essential for the proper functioning of the cell and/or organism.

Mitochondria

• Present in eukaryotic animal and plant cells.
• Their primary function is energy generation through cellular respiration (ATP production).
• A sausage-shaped organelle with a double membrane.
• The inner membrane has many folds called cristae.
• The double membrane allows for the organization of various stages of the respiratory chain, making it crucial for cellular function and survival.

Cellular Digestion

• Involves breaking down molecules and unwanted materials, enabling the recycling of nutrients and cellular maintenance.

Lysosomes

• These are dense spherical sacs that contain digestive enzymes.
• They break down molecules and unwanted cellular materials.
• They facilitate cellular digestion by disposing of waste through breaking down worn-out cell parts, recycling nutrients, and defending against pathogenic invasions.

Peroxisomes

• Contain enzymes that degrade hydrogen peroxide and toxic compounds.
• They protect the cell from oxidative damage.
• Contain oxidase enzymes to detoxify substances such as alcohol.
• Catalase converts hydrogen peroxide to water and oxygen.
• Play a role in the synthesis and degradation of lipids and bile acids, regulating lipid metabolism and overall homeostasis.

Biological drawings

• Should be accurate enough to serve as a record of an observation.
• Clear, simple, and properly labeled.
• Draw only what you see, not what you think you see
• The size of the specimen drawing needs to be in scale with its actual ratio to the size of the field view.
• Labels need to be placed beside the drawing.
• No need to use arrowheads to point on structures.
• Figure legend Placement below the figure.
• Provide a title, and as appropriate, a statement briefly describing the figure.
• They specimen/source organism's scientific name also need to be specified.
• For microscope specimen, indicate the total magnification used.
• Total magnification = ocular lens x objective lens
• Accuracy, Scaling, Labels, Figure title, and Total magnification are the most important factors