12. Biología Celular: Clasificación de las células

General Characteristics of Cells

In this section, the tutor introduces the general characteristics of cells, focusing on the differentiation between eukaryotic and prokaryotic cells.

Cell Structure and Function

• Cells are fundamental structures that serve as the functional and structural units of life, enclosed by a plasma membrane regulating substance passage.

• Genetic material in the form of DNA is found within cells, carrying vital genetic information.

• Cells are categorized into two main groups based on the presence or absence of a nucleus: prokaryotic cells lack a defined nucleus, while eukaryotic cells have a well-defined nucleus.

Prokaryotic Cells

• Prokaryotic cells contain genetic material in the form of a single circular DNA strand loosely associated with non-histone proteins in an area called nucleoid.

• Essential structures in prokaryotic cells include a plasma membrane, circular double-stranded DNA, and a cell wall composed of peptidoglycan.

Membrane and Cell Wall Composition

• The plasma membrane in prokaryotic cells is lipid-based and crucial for cellular processes like photosynthesis and respiration.

• The cell wall consists mainly of peptidoglycan, distinguishing it from eukaryotic cell walls which will be discussed later.

Cellular Components in Prokaryotes

This part delves deeper into specific components present in prokaryotic cells such as flagella, pili, and nucleoid.

Additional Prokaryotic Structures

• Prokaryotes may exhibit an outer cell membrane similar to the inner one but interrupted by pores or proteins known as porins.

• The nucleoid houses a large circular bacterial chromosome within the cytoplasm without being enclosed by a distinct nuclear envelope.

Flagella and Pili Functions

• Flagella aid in cellular motility through protein motor projections embedded within the plasma membrane.

General Characteristics of Prokaryotic Cells

In this section, the focus is on the exchange of genetic material in prokaryotic cells, emphasizing the significance of plasmids and ribosomes in these cells.

Material Exchange in Prokaryotic Cells

• Plasmids are additional genetic materials found in prokaryotes, contained in small DNA strands.

• These circular plasmids are crucial as they can carry genetic material for expressing various genes that provide adaptative characteristics to prokaryotes.

Ribosomes in Prokaryotic Cells

• Ribosomes in prokaryotes have a similar general structure to all living organisms.

• Comprising a larger subunit with a sedimentation coefficient of 70s and a smaller subunit with a sedimentation coefficient of 30s.

• The sedimentation coefficient is a physical parameter used to characterize molecules based on their centrifugation speed per unit centrifugal force applied to a sample.

Reproduction and Gram Staining in Prokaryotic Cells

This section delves into the reproduction mechanism of prokaryotic cells through binary fission and introduces the concept of Gram staining for bacterial identification.

Reproduction Mechanism

• Prokaryotic cells primarily reproduce through binary fission, where the cell enlarges, duplicates its genetic material, and then divides into two daughter cells, each carrying a copy of the genetic material.

Gram Staining Technique

• Gram staining is a routine laboratory practice that differentiates between gram-negative (pink) and gram-positive (purple) bacteria.

• This technique aids in identifying bacterial types present in samples like patient cultures or soil characterizations.

Cell Types within Prokaryotes

The discussion shifts towards differentiating cell types within prokaryotes, particularly focusing on bacteria and archaea as representative groups.

Cell Classification

• Bacteria represent one of the most prominent groups within prokaryotes alongside archaea.