Cells and Cellular Transport

Cell History Hooke - is the scientist who 1st coined the term “cell” – in the 1660’s he observed cork from a tree stem (they reminded him of the rooms monks lived in) Schleiden looked at plant cells & Schwann looked at animal cells. They both observed that cells make up all parts of an organism. Along with Virchow they formulated the Cell Theory.

Schleiden Schwann Virchow

The Cell Theory 1. All living things are composed of cells 2. Cells are the basic units of structure and function in living things 3. New cells are produced from existing cells

Cell Size The surface area of the cell does not increase at the same rate as the volume. Because of this, cells typically stay small & will divide rather than getting larger.

Cell Organization Prokaryotic vs. Eukaryotic There are 2 basic types of cells: – Prokaryotic and Eukaryotic Prokaryotic Cells: – NO TRUE NUCLEUS – No membrane bound organelles – Bacteria Eukaryotic Cells: – Has a nucleus surrounded by a nuclear membrane – Plant and Animal Cells

Cell Organization Plants vs. Animals Plant Cells – Cell wall – Chloroplast – Contain larger vacuoles Animal Cells – centrioles

Parts of the Cell 1. Nucleus - control center of the cell – controls most of the activities of the cell ; also transmits hereditary information & contains DNA. The nucleus holds chromosomes (threadlike) that are seen only when the cell is dividing & chromatin (granular) when the cell isn’t dividing.

2. Nucleoli - these are found in the nucleus – where the assembly of ribosomes begins. 3. Nuclear envelope - double membrane - this surrounds the nucleus & acts as a boundary between the nucleus & the cytoplasm – it contains pores that allow substances to pass

4. Cell membrane - this acts as the outer boundary of the cell & contains phospholipids & proteins - it is very important because it regulates what enters & leaves the cell

The Cell Membrane The main purpose of the cell membrane is to regulate the movement of materials into and out of the cell. Semi-permeable: meaning that only certain substances can go through

The Cell Membrane cont. The cell membrane is composed of a phospho- lipid bilayer = 2 layers of lipids Each layer consist of: – Phosphate group attached to 2 fatty acid tails – Phosphate heads make up the outside while the fatty acid tails are composed toward the inside – Proteins are embedded within the bilayer to help transport substances into and out of the cell.

5. Cell wall - this is found in plants, algae, fungi, & bacteria- it protects & supports the cell – it lies outside of the cell membrane & allows water & gases to pass through – plant cell walls are made of cellulose

6. Cytoplasm - is the jellylike layer of the cell – it contains the organelles & moves materials throughout the cell in a process called cytoplasmic streaming

7. Endoplasmic reticulum - this is a series of canals or channels that winds through the cytoplasm – it acts as the cell’s internal transport & connects with the nuclear envelope; there are 2 types – (1) smooth ER- this builds lipids for the plasma membrane, (2) Rough ER - has ribosomes attached - Protein synthesis

8. Ribosomes- the sites of protein synthesis; 2 types (1) Free - makes protein to be used in the cell, (2) Bound - make protein to be transported out of the cell

9. Golgi Bodies - these pinch off from the ER – they are stacks of membranes that look like tiny flattened balloons – they are areas for storage & packaging of chemicals – enzymes in this apparatus attach carbohydrates & lipids to proteins

10. Mitochondria - the cell’s powerhouse – they produce the energy for the cell – they have many folds on the inside called cristae that increase surface area for more energy

11. Plastids - are found only in plants – some store food, others have pigments – 3 types: (1) Leucoplasts - colorless – store starches in roots & stems (2) Chromoplasts - they are orange & yellow – beta carotene (3) Chloroplasts - these are green & the sites for photosynthesis

12. Vacuoles - bubblelike storage structures that store water, liquids, wastes, & foods – these hold plants erect & firm

13. Lysosomes - these are membrane-bound organelles that are formed in Golgi bodies – they are loaded with enzymes that digest large particles found in the cell – also break down old organelles

14. Microtubules - hollow cylinders of protein that support & shape the cell – found in the cytoskeleton, spindle fibers, centrioles, basal bodies, cilia, & flagella

15. Spindle fibers - appear during cell division & move chromosomes through the cytoplasm

16. Centrioles - small dark bodies located outside the nucleus – they are active during cell division

17. Cilia - short, threadlike structures used for movement – they are numerous & hairlike

18. Flagella - long, whiplike structures used for movement – usually only 1 per cell

19. Cytoskeleton - network of protein filaments that helps the cell to maintain its shape – also involved in cell movement - these are made of: a) microtubules - hollow tubes of protein – maintain cell shape & serve as “tracks” along which organelles are moved (used to make cilia & flagella) b) microfilaments - long, thin fibers that function in the movement & support of the cell – tough, flexible framework that supports the cell

Cellular Transport Passive Transport: does NOT require energy – Molecules move from an area of high concentration to an area of low concentration 1. Diffusion: substances move directly through the cell membrane

Cellular Transport cont. 2. Facilitated Diffusion: uses channel proteins to move a substance through the cell membrane

Cellular Transport cont. 3. Osmosis: The movement of WATER from an area of high water concentration to an area of low water concentration – Can occur in either direction

Cellular Transport Osmosis Solution Concentrations: – Hypotonic: solution has lower concentration of solute---higher concentration of water Cell Swells – Hypertonic: solution has a higher concentration of dissolved solute---lower concentration of water Cell Shrinks – Isotonic: net concentration of dissolved solutes are the same inside and outside of the cell. Cell remains the same

Cell Transport Active Transport: Requires energy – Movement of substances from an area of low concentration to an area of high concentration – Occurs against the concentration gradient 1. Exocytosis: removes materials from the cell 2. Endocytosis: Brings materials into the cell