Biology Lecture 3: Cell Structure

Cell Biology

• The cell is the basic functional and structural unit of life, playing a vital role in all biological activities.
• All cells are composed of four chemical components: proteins, nucleic acids, lipids, and polysaccharides.

Prokaryotes vs Eukaryotes

• Every living organism falls into one of two groups: prokaryotes or eukaryotes, distinguished by their cellular structure.
• Prokaryotes lack membrane-bound structures, including a nucleus, and are typically small and simple cells.
• Prokaryotes can be split into two domains: bacteria and archaea.
• Prokaryotic cells have a central region called the nucleoid, where DNA is bundled together.

Prokaryotic Cell Features

• Nucleoid: a central region containing DNA.
• Ribosomes: responsible for protein synthesis.
• Cell wall: provides structure and protection.
• Cell membrane: separates the cell from the outside environment.
• Capsule: a layer of carbohydrates surrounding the cell wall, helping with attachment.
• Fimbriae: thin, hair-like structures for cellular attachment.
• Pili: rod-shaped structures involved in attachment and DNA transfer.
• Flagella: thin, tail-like structures assisting in movement.

Eukaryotic Cell

• Eukaryotes are more complex and larger than prokaryotes, with a true nucleus and other membrane-bound organelles.
• Eukaryotic cells have a cell wall, plasma membrane, and organelles responsible for various functions.
• Eukaryotes include almost all major kingdoms except kingdom monera.

Eukaryotic Cell Features

• Nucleus: stores genetic information in chromatin form.
• Nucleolus: where ribosomal RNA is produced.
• Plasma membrane: surrounds the cell and encompasses organelles.
• Cytoskeleton or cell wall: provides structure, allows for cell movement, and plays a role in cell division.
• Ribosomes: responsible for protein synthesis.
• Mitochondria: responsible for energy production.
• Cytoplasm: the region between the nuclear envelope and plasma membrane.
• Cytosol: a gel-like substance containing organelles.
• Endoplasmic reticulum: involved in protein maturation and transportation.
• Vesicles and vacuoles: membrane-bound sacs for transportation and storage.

Key Similarities between Prokaryotes and Eukaryotes

• All cells share four features: DNA, plasma membrane, cytoplasm, and ribosomes.

Transcription and Translation

• In prokaryotic cells, transcription and translation are coupled, occurring simultaneously.
• In eukaryotic cells, transcription and translation are not coupled, with transcription occurring in the nucleus and translation in the cytoplasm.

Key Differences between Prokaryotes and Eukaryotes

• Structural variation: presence or absence of a nucleus and membrane-bound organelles.
• Molecular variation: circular or linear DNA form.

Cell: The Basic Unit of Life

• A cell is the basic functional and structural unit of life, playing a vital role in all biological activities.
• Cells consist of four chemical components: proteins, nucleic acid, lipids, and polysaccharides.
• Cells have membrane-bound organelles that perform individual functions to keep the cell alive and active.

Prokaryotes vs Eukaryotes

• Prokaryotes and eukaryotes are the two groups of living organisms, distinguished by their cellular structure.
• Prokaryotes are ancient, with fossil records dating back to 3.5 billion years ago, and can be split into two domains: bacteria and archaea.
• Prokaryotes are unicellular, lack membrane-bound structures, and have a nucleoid region instead of a nucleus.

Prokaryotic Cell Features

• Nucleoid: a central region containing DNA.
• Ribosome: responsible for protein synthesis.
• Primitive organelles, such as micro-compartments, provide some organization to the cell.

Key Similarities between Prokaryotes and Eukaryotes

• All cells share four features: DNA, plasma membrane, cytoplasm, and ribosomes.

Transcription and Translation

• In prokaryotes, transcription and translation are coupled, with translation beginning during mRNA synthesis.
• In eukaryotes, transcription and translation are not coupled, with transcription occurring in the nucleus and translation in the cytoplasm.

Key Differences between Prokaryotes and Eukaryotes

• Structural differences: presence or absence of a nucleus and membrane-bound organelles.
• Molecular differences: circular or linear DNA arrangement.
• Other differences include cell size, cell wall, ribosomes, mitochondria, cytoplasm, endoplasmic reticulum, plasmids, and lysosomes.

Cell Division and Reproduction

• Prokaryotes divide through binary fission.
• Eukaryotes divide through mitosis.
• Prokaryotes reproduce asexually, while eukaryotes can reproduce both asexually and sexually.