Cell Anatomy and Composition

Cell Anatomy

• Robert Hooke (1635-1703) described cells in 1665 as "cellulae" after observing thin slices of cork, noting their porous, honeycomb-like appearance.
• Anton van Leeuwenhoek (1632-1723) is known for observing microscopic entities from pond water, which he named "animalcules", using his own self-made microscope for biological specimens
• The cell theory states that all living things are made of cells, cells are the basic units of structure and function, and new cells come from existing cells through cell division.

Cell Composition

• Cells come in prokaryotic and eukaryotic forms.
• Prokaryotic cells lack a true nucleus, while eukaryotic cells possess a true nucleus and membrane-bound organelles.
• The cell is the basic functional and structural unit of life, playing a role in biological activities through its membrane-bound organelles.

Plant vs Animal Cells

• Plant cells have a rigid cell wall, large central vacuole, and chloroplasts, but lack centrosomes and lysosomes.
• Animal cells lack a cell wall and chloroplasts, but have numerous small vacuoles, centrioles/centrosomes, and lysosomes
• Cells come in two types: prokaryotic and eukaryotic.
• Prokaryotic cells lack a true nucleus while eukaryotic cells have a true nucleus.

Prokaryotic Cells

• They are independent, single-celled organisms like bacteria and cyanobacteria.
• Small in size with simple internal structures.
• The nucleoid region contains DNA.
• Have a peptidoglycan cell wall with a polysaccharide capsule.
• Ribosomes are present in the cytoplasm.
• Some include flagella, pili, or fimbriae for movement or attachment.
• Genetic material is present on a single chromosome.
• Histone proteins are lacking.
• The cell wall is made with carbohydrates and amino acids.
• The plasma membrane carries respiratory enzymes.
• Reproduction occurs asexually via binary fission, or sexually via conjugation.

Eukaryotic Cells

• Eukaryotes include protists, fungi, animals, and plants.
• Cells are larger than prokaryotic cells, allow for compartmentalization, housing membrane-bound organelles for specialized functions.
• Chromosomes and DNA are located inside of the nucleus
• Cell structures are minute filaments and tubules within the cytoskeleton that gives shape to the cell and allows for movement.

Prokaryotic Cell Structure

• All prokaryotic cells have a plasma membrane enclosing DNA, ribosomes, and cytoplasm.
• Some have a cell wall for protection and shape, a capsule for extra protection, and pili for attachment.
• Hair-like pili facilitate attachment to surfaces, sometimes aiding in DNA transfer.
• Flagellum move through cellular movement
• Glycocalyx/Capsule is an outer protective covering found with a slime layer which attached loosely
• Capsule stimulates antibody production.
• The cell wall supports peptidoglycan and protects cells from osmotic damage
• Gram-positive bacteria have multi-layered cell walls, unlike single-layered gram-negative bacteria.
• Prokaryotic cell cytoplasm consists of enzymes, salts and molecules
• The cell's plasma membranes surround the cytoplasm and control the entry and exit of substances
• Pili or fimbriae aid in bacterial reproduction to conjugate cells.
• Axial filaments (endoflagella) are found with spirochetes that aide movement
• Plasmids and non-chromosomal molecules of DNA and are used for beneficial traits like antibiotic resistance

Prokaryotic Internal Structure

• Ribosomes aid protein production.
• Granules/Inclusion bodies store food and energy, with examples being granules found inside of Corynebacterium diphtheriae and M.tuberculosis
• Mesosomes play a role in DNA replication and aids cell divison
• Endospores are formed inside of bacteria in harsh conditions needed to survive

Cell Size Differences

• Prokaryotic cells are smaller at 0.1 to 5.0 micrometers whereas eukaryotic cells are considerably larger ranging at 10-100 micrometers

Gram-Positive Bacteria Distinctions

• Thick peptidoglycan cell wall
• Lacks an additional outer membrane
• Has teichoic acids with anionic polymers

Gram-Negative Bacteria Distinctions

• Thin peptidoglycan cell wall that is surrounded by a outer membrane
• Additional proteins and lipids like porins are used for membrane transport

Four Main Components of Prokaryotic Cells:

• The plasma membrane is an outer protective layer of phospholipid that isolates the cell from the surrounding environment.
• The cytoplasm is a jelly-like substance of all the cells organelles suspended in the cell
• DNA is the genetic material of cells that regulates the actions of the cell and creates proteins.
• Ribosomes are where synthesis occurs

Prokaryotic Cell Reproduction

• Prokaryotes reproduce in two main ways: asexually via binary fission (division into identical daughter cells) and sexually through conjugation which helps swap DNA.
• In binary fission, a cell divides into two identical daughter cells in as little as 20 minutes
• In conjugation, bacteria builds a sex pilus and swaps DNA and plasmids with another bacteria
• Asexual binary fission involves a singular parent
• Sexual Conjugation occurs between two parents

Prokaryotic Cell Recombination

• Transformation involves DNA introduced by the bacterial cell
• Transduction is a process done with viruses to transfer materials into cells