Cell Structure and Function

Transcription

1 Cell Structure and Function Chapter What is a Cell? Each cell has a plasma membrane, cytoplasm, and a nucleus (in eukaryotic cells) or a nucleoid (in prokaryotic cells) 1

2 Nucleoid concentrated DNA in the cytoplasm Cytoplasm Semifluid mixture of Water Ions Sugar Proteins Suspends organelles Plasma membrane outer membrane. Regulates inner metabolic activities from environment. Passes freely Water CO2 O2 Others move by gate cytoplasm DNA plasma membrane a Bacterial cell (prokaryotic) Fig. 4.3, p. 52 cytoplasm DNA in nucleus Nucleus double membrane sac plasma membrane b Plant cell (eukaryotic) Fig. 4.3, p. 52 2

3 cytoplasm DNA in nucleus plasma membrane c Animal cell (eukaryotic) Fig. 4.3, p. 52 Components of Cell Membranes Lipid bilayer Hydrophilic head Hydrophobic tails 3

4 Arranged so the hydrophobic ends are sandwiched between hydrophilic ends. fluid fluid lipid bilayer Fig. 4.4, p. 53 Protein channels Proteins channels Channels through bilayer Pump substances across 4

5 extracellular environment one layer of lipids one layer of lipids cytoplasm membrane protein Fig. 4.4, p. 53 Cell Size and Shape Big enough to see Yolk and fish eggs Surface-to-volume ratio limits cell size When a cell expands in diameter during growth, its volume increases faster than its surface area does Point not enough surface area to pass nutrients and waste to maintain the cell. One way around long thin cells 5

6 Key Concepts: WHAT ALL CELLS HAVE IN COMMON Each cell has a plasma membrane, a boundary between its interior and the outside environment The interior consists of cytoplasm and an innermost region of DNA 4.2 How Do We See Cells? Three key points of the cell theory: All organisms consist of one or more cells The cell is the smallest unit that retains the capacity for life A cell arises from the growth and division of another cell 6

7 Microscopes Different microscopes use light or electrons to reveal details of cell shapes or structures Key Concepts: MICROSCOPES Microscopic analysis supports three generalizations of the cell theory: Each organism consists of one or more cells and their products A cell has a capacity for independent life Each new cell is descended from a living cell 7

8 4.3 Membrane Structure and Function Each cell membrane is a boundary (lipid bilayer) that controls the flow of substances across it Fluid mosaic model Membrane is composed of phospholipids, sterols, proteins, and other components Phospholipids drift within the bilayer Barrier to water soluble molocules Membrane Proteins Many proteins are embedded in or attached to cell membrane surfaces Receptors trigger changes in cell activities when activated by outside stimuli Transporters Span membrane and move substances across cell membrane communication proteins allows substances to flow from one cell to another adhesion proteins helps cells migrate to certain regions then stay there 8

9 Membrane Proteins Plasma (outer) membrane also incorporates recognition proteins identifies cell Common Membrane Proteins 9

10 Membrane Structure Studies COMPONENTS OF CELL MEMBRANES Membrane composition is determined by cells function 10

11 Key Concepts: COMPONENTS OF CELL MEMBRANES All cell membranes are mostly a lipid bilayer (two layers of lipids) and a variety of proteins The proteins have diverse tasks, including control over which water-soluble substances cross the membrane at any given time 4.4 Introducing Prokaryotic Cells Bacteria and archaeans The simplest cells The groups with greatest metabolic diversity Biofilms Shared living arrangements of prokaryotes 11

12 Prokaryote Structure Cell wall Surrounds plasma membrane Rigid and porous Flagella Used for motion like a propeller Pili Protein filaments used for attachment Sex pilus transfers genetic material Prokaryote Structure Ribosomes in cytoplasm Makes proteins DNA Circular Single chromosome Plasmid extra genetic material that may help with antibiotic resistances 12