Chapter 4 A Tour of the Cell

History of Cells

Robert Hooke - Observed cells in cork.

Coined the term "cells” in 1665.

History of Cells 1833 - Robert Brown,

discovered the nucleus. 1838 - M.J. Schleiden,

all plants are made of cells. 1839 - T. Schwann,

all animals are made of cells. 1840 - J.E. Purkinje, coined

the term “protoplasm”.

Cell Theory

All living matter is composed of one or more cells.

The cell is the structural and functional unit of life.

R. Virchow

“Omnis cellula e cellula” All cells are from other cells.

Why Are Cells So Small?

Cell volume to surface area ratios favor small size.

Big enough to perform all functions but have enough surface area

Nucleus to cytoplasm consideration (control all areas).

Metabolic requirements.

Basic Cell Organization

Membrane Nucleus Cytoplasm Organelles

Animal Cell

Plant Cell

Membrane

Separates the cell from the environment.

Boundary layer for regulating the movement of materials in/out of a cell.

Cytoplasm or Cytosol

Cell substance between the cell membrane and the nucleus.

The “fluid” part of a cell. Exists in two forms: gel - thick sol - fluid

Organelle

Term means "small organ” Formed body in a cell with a specialized function.

Important in organizational structure of cells.

Organelles - function

Way to form compartments in cells to separate chemical reactions.

Keeps various enzymes separated in space.

Nucleus

Most conspicuous organelle. usually spherical, but can be

lobed or irregular in shape.

Structure

Nuclear membrane Nuclear pores Nucleolus Chromatin

Nuclear Membrane

Double membrane Inner membrane supported

by a protein matrix to provide shape

Nuclear Pores

Allow things in and out of nucleus

Ex. mRNA during transcription

Nucleolus

Dark staining area in the nucleus.

0 - 4 per nucleus. Storage area for ribosomes.

Chromatin

Chrom: colored - tin: threads DNA and Protein in a “loose”

format. Will form the cell’s chromosomes.

Nucleus - Function

Contains the genetic instructions to make proteins and more DNA

Ribosomes

Structure: 2 subunits made of protein and rRNA. No membrane.

Function: protein synthesis. Site of translation

Subunits

Large: 45 proteins 3 rRNA molecules

Small: 23 proteins 1 rRNA molecule

Locations

Free in the cytoplasm - make proteins for use in cell.

Membrane bound - make proteins that are exported from the cell. (on rough ER)

Endomembrane System

Membranes that are related through direct physical continuity or by the transfer of membrane segments called vesicles.

Endomembrane System

Endoplasmic Reticulum

Often referred to as ER. Makes up to 1/2 of the total

membrane in cells. Often continuous with the

nuclear membrane.

Structure of ER

Folded sheets or tubes of membranes.

Very “fluid” in structure with the membranes constantly changing size and shape.

Types of ER

Smooth ER: no ribosomes. Used for lipid synthesis,

carbohydrate storage, detoxification of poisons.

Rough ER: with ribosomes. Makes secretory proteins.

Golgi Apparatus or Golgi Body

Structure: parallel array of flattened cisternae. (looks like a stack of pancakes)

3 to 20 per cell. Likely an outgrowth of the ER

system.

Function of Golgi Bodies

Processing - modification of ER products (lipids, carbs).

Distribution - packaging of ER products for transport.

Mailman of the cell

Golgi Vesicles

Small sacs of membranes that bud off the Golgi Body.

Transportation vehicle for the modified ER products.

Lysosome

Structure: Single membrane. Made from the Golgi

apparatus.

Function

Breakdown and degradation of cellular materials.

Contains enzymes for fats, proteins, polysaccharides, and nucleic acids.

Over 40 types known.

Lysosomes

Important in cell death. Missing enzymes may cause

various genetic enzyme diseases.

Examples: Tay-Sachs, Pompe’s Disease

Vacuoles

Structure - single membrane, usually larger than the Golgi vesicles.

Function - depends on the organism.

Protists

Contractile vacuoles - pump out excess water.

Food vacuoles - store newly ingested food until the lysosomes can digest it.

Plants

Large single vacuole when mature making up to 90% of the cell's volume.

Function

Water regulation. Storage of ions. Storage of hydrophilic

pigments. (e.g. red and blues in flower petals).

Function: Plant vacuole

Used to enlarge cells and create turgor pressure.

Enzymes (various types). Store toxins. Coloration.

Microbodies: Peroxisomes

Structure: single membrane. Often have a granular or

crystalline core of enzymes.

Function

Specialized enzymes for specific reactions.

Peroxisomes: use up/break down hydrogen peroxide.

Enzymes in a crystal

End of part 1 Homework

Mitochondria

Structure: 2 membranes. The inner membrane has more surface area than the outer membrane.

Matrix: inner space. Intermembrane space: area between

the membranes.

Inner Membrane

Folded into cristae. Amount of folding depends

on the level of cell activity. Contains many enzymes. ATP generated here.

Function

Cell Respiration - the release of energy from food.

Major location of ATP generation.

“Powerhouse” of the cell.

Mitochondria notes

Have ribosomes (small size). Have their own DNA. Can reproduce themselves. May have been independent

cells at one time.

Chloroplasts

Structure - two outer membranes.

Complex internal membrane. Fluid-like stroma is around

the internal membranes.

Inner or Thylakoid Membranes

Arranged into flattened sacs called thylakoids.

Some regions stacked into layers called grana.

Contain the green pigment chlorophyll.

Function

Photosynthesis - the use of light energy to make food.

Where does this food go to produce energy?

Chloroplasts notes

Contain ribosomes (small size). Contain DNA. Can reproduce themselves. May have been independent

cells at one time.

Cytoskeleton

Network of rods and filaments in the cytoplasm.

Functions

Cell structure and shape. Cell movement. Cell division - helps build cell

walls and move the chromosomes apart.

Components

Microtubules Microfilaments Intermediate Filaments

Microtubules

Structure - small hollow tubes made of repeating units of a protein dimer.

Level 3-Size - 25 nm diameter with a 15 nm lumen. Can be 200 nm to 25 m in length.

Tubulin

Protein in microtubules. Dimer - and tubulin.

Microtubules

Regulate cell shape. Tracks for motor molecules.

Microtubules

Form cilia and flagella. Internal cellular movement. Make up centrioles, basal

bodies and spindle fibers.

Centrioles

Usually one pair per cell, located close to the nucleus.

Found in animal cells. 9 sets of triplet microtubules. Help in cell division.

Microfilaments

5 to 7 nm in diameter. Structure - two intertwined

strands of actin protein.

Microfilaments are stained green.

Functions

Muscle contraction. Cytoplasmic streaming. Pseudopodia. Cleavage furrow formation. Maintenance and changes in

cell shape.

Intermediate filaments

Fibrous proteins supercoiled into cables

Functions: Maintain cell shape

Anchor organelles

Cytoskeleton

Very dynamic; changing in composition and shape frequently.

Cell is not just a "bag" of cytoplasm within a cell membrane.

Cell Wall

Nonliving jacket that surrounds some cells.

Found in: Plants Prokaryotes Fungi Some Protists

Cell Walls

May be made of other types of polysaccharides and/or silica.

Function as the cell's exoskeleton for support and protection.

Extracellular Matrix - ECM

Fuzzy coat on animal cells. Helps glue cells together. Made of glycoproteins and

collagen. Evidence suggests ECM is

involved with cell behavior and cell communication.

Intercellular Juctions

Plants-Plasmodesmata

Plasmodesmata

Channels between cells through adjacent cell walls.

Allows communication between cells.

Also allows viruses to travel rapidly between cells.

Intercellular Juctions

Animals: Tight junctions Anchoring junctions Gap junctions

Tight Junctions

Very tight fusion of the membranes of adjacent cells.

Seals off areas between the cells.

Lining of digestive tract

Anchoring junctions

Does not close off the area between adjacent cells.

Coordination of movement between groups of cells.

Ex: Tissue subject to stretching (skin and muscle)

Gap Junctions

Open channels between cells, similar to plasmodesmata.

Allows “communication” between cells.

Ex: heart muscle, embryos

Types of Cells

Prokaryotic - lack a nucleus and other membrane bound structures.

Eukaryotic - have a nucleus and other membrane bound structures.

Both Have:

Membrane Cytosol Ribosomes (but the size is

different)

Prokaryotic Eukaryotic

Nucleus

Prokaryotes

Bacteria Capsule- sticky outer layer Cell wall- protects and

maintains shape Plasma membrane- controls

movement of materials

Prokaryotes

Pili- used for attachment Joins bacteria together for

transfer of DNA Flagella- allow for cell motility

(longer than pili)

Prokaryotes

Ribosomes- protein synthesis Nucleoid- Contains the DNA

Calculating in microscopes

Actual size of specimen Measure the field of vision

while looking through the microscope (~1.5mm)

Then figure the % of field the specimen occupies and multiply by field of vision

Continued

Field of vision is 1.4mm or 1400 micrometers

Specimen is 60% of field of vision

1400 x .60 =840 micrometers

Calculating

Magnification Scale bar next to drawing

Magnification= size of image / size of specimen

Size of image = 10 mm or 10000 micrometers

Size of specimen is 10 micrometers

10000 / 10 is 1000x magnified

Magnification

Image size 12.5 cm or

125,000

Micrometers

Specimen size

(using scale)

4.5 micrometers

So 125,000/4.5=

27,777x

Summary

Answer: Why is Life cellular and what are the factors that affect cell size?

Be able to identify cellular parts, their structure, and their functions.