Cell membranes are crucial for concentrating nutrients and retaining them for:
Energy production
Building cellular molecules
All cells must synthesize proteins, facilitated by ribosomes.
Ribosome presence:
Varies by cell type (1 to thousands)
Essential for protein synthesis.
Definition: Jelly-like substance inside cells (fluid-filled).
Functions:
Surrounds all cellular structures not clearly visible.
Similar to the interstitial fluid in organisms.
Concentrates molecules from the environment for cellular needs.
Introduction to organelles: Tour through various organelles begins.
Control center of the cell:
Contains DNA
Has a double membrane (nuclear envelope):
Composed of an inner and outer membrane with space in-between.
Function of double membrane:
Slows diffusion to protect DNA and nuclear contents.
Pores in the membrane permit selective transport in/out.
Special pores can close if DNA approaches, protecting it from cytoplasmic enzymes.
Importance of nucleus in cellular processes:
Prevents destruction of DNA from enzymes targeting rogue DNA (potential viruses).
RNA can exit the nucleus through pores (different from DNA's restricted movement).
Nucleolus structure:
Region within the nucleus where DNA is concentrated.
Contains chromatin made from DNA wrapped around proteins for organization.
Chromatin vs. chromosomes:
Chromatin: Loosely organized DNA during non-dividing periods.
Chromosomes: Tightly wound, visible during cell division (mitosis).
Involvement in ribosome production:
Nucleolus synthesizes ribosomal RNA (rRNA) that forms ribosomes.
Composition:
Made of ribosomal RNA and proteins.
Consist of two subunits (small and large).
Ribosome sizes in different cell types:
Prokaryotes:
Small subunit: 30S
Large subunit: 50S
Total functional ribosome: 70S
Eukaryotes:
Small subunit: 40S
Large subunit: 60S
Total functional ribosome: 80S
Significance of difference in ribosome structure:
Allows antibiotic targeting (e.g., macrolide antibiotics target bacterial ribosomes without affecting eukaryotic ribosomes).
Importance for certain cells:
Cells like those in the pancreas producing insulin have many ribosomes (thousands) due to constant protein production.
Muscle fibers also contain numerous ribosomes for repairing proteins damaged by movement.