Chapter 3, part 3
An Introduction to
The Cellular Level of Organization
SECTION 3-4
The Nucleus
Surrounded by a nuclear envelope
Perinuclear space
Communicates with cytoplasm through nuclear pores
The nucleus is the center of cellular operations
Figure 3.13 The Nucleus
Figure 3.13
A supportive nuclear matrix
One or more nucleoli
Chromosomes
DNA bound to histones
Chromatin
Contents of the nucleus
Figure 3.14 Chromosome Structure
Figure 3.14
The cells information storage system
Triplet code
A gene contains all the triplets needed to code for a specific polypeptide
The genetic code
Gene activation initiates with RNA polymerase binding to the gene
Transcription is the formation of mRNA from DNA
mRNA carries instructions from the nucleus to the cytoplasm
Gene activation and protein synthesis
Figure 3.16 An overview of Protein Synthesis
Figure 3.16
A functional polypeptide is constructed using mRNA codons
Sequence of codons determines the sequence of amino acids
Complementary base pairing of anticodons (tRNA) provides the amino acids in sequence
Translation is the formation of a protein
Figure 3.17 The Process of Translation
Figure 3.17
Figure 3.17 The Process of Translation
Figure 3.17
SECTION 3-5
How Things Get Into and Out of Cells
The ease with which substances can cross the cell membrane
Nothing passes through an impermeable barrier
Anything can pass through a freely permeable barrier
Cell membranes are selectively permeable
Permeability
Movement of a substance from an area of high concentration to low
Continues until concentration gradient is eliminated
Diffusion
Figure 3.18 Diffusion
Figure 3.18
Figure 3.19 Diffusion across the Cell Membrane
Figure 3.19
Diffusion of water across a semipermeable membrane in response to solute differences
Osmotic pressure = force of water movement into a solution
Hydrostatic pressure opposes osmotic pressure
Water molecules undergo bulk flow
Osmosis
Figure 3.20 Osmosis
Figure 3.20
The effects of osmotic solutions on cells
Isotonic = no net gain or loss of water
Hypotonic = net gain of water into cell
Hemolysis
Hypertonic = net water flow out of cell
Crenation
Tonicity
Figure 3.21
Figure 3.21 Osmotic flow across a cell membrane