Chapter 4Cell Structure

I. Cell Theory (4.1)

• Hooke first observed cells 1665

• Leeuwenhoek first observed live cells.

• 1838-9 Schleiden and Schwann.

A. Cell theory is the unifying foundation of cell biology

1. All organisms are made of cells.

2. Cells are the basic units of life.

3. Cells are made through division of preexisting cells.

B. Cell size is limited

1. Surface area – to – volume ratio: molecules can more through the membrane quickly if they are close in small cells;

surface area = r2 but volume = r3.

C. Microscopes allow visualization of cells and components 1. Resolution: clarity; minimum distance 2

can be apart and still seen as 2 separate points.

2. Types of Microscopes

1. Light: uses light and 2 lenses

2. Compound: uses multiple lenses

1. Electron: electron beams

2. Transmission electron: see through specimen

3. Scanning electron: look at surface of specimen

3. Using stains to view cell structure

• Stains: cause some structures to become darker for contrast helping resolution.

D. All cells exhibit basic structural similarities

• Nucleus or nucleoid

• Cytoplasm

• Ribsomes

• Plasma membrane

1. Centrally located genetic material

i. Prokaryotes: simple organisms, most genetic material is circular DNA

ii. Nucleoid: area near center of cell where genetic material found (no membrane separating it)

iii. Eukaryote: complex organisms, contain nucleus and organelles.

iv. Nucleus: organelles w/ DNA

2. Cytoplasm

1. Cytoplasm: jelly-like matrix that fills inside of cell

2. Organelle: membrane-bound structure w/ specific job

3. Cytosol: part of cytoplasm with organic molecules (like proteins, sugars) and ions

Cytoplasm

O

R

G

A

N

E

L

L

E

S

3. Plasma Membrane

i. Phospholipid bilayer: 2 layers of lipids around cell, separate contents from surroundings

ii. Transport proteins: help move material across membrane

iii. Receptor proteins: help cells communicate, send and receive messages

II. Prokaryotic Cells (4.2)

• No nucleus

• No organelles

A. Prokaryotic cells have relatively simple organization 1. Cell wall: provides structure; outside of

cell membrane and cytoplasm

2. Ribosomes: carry out protein synthesis

3. 2 types: archaea and bacteria

4. Cell membrane can take on other jobs

5. Functions as 1 whole unit

B. Bacterial cell walls consist of peptidoglycan 1. Peptidoglycan: made of a carbohydrate

that provides structure, protection, and water balance

2. Gram-positive: group of bacteria w/ single layer of cell wall that holds violet dye

3. Gram-negative: group of bacteria with multilayer cell wall that does NOT hold violet dye.

C. Archaea lack peptidoglycan

D. Some prokaryotes move by means of rotating flagella 1. Flagella: threadlike structures made of

protein fibers used for locomotion

III. Eukaryotic Cells (4.3)

1. Endomembrane system: membrane bound sections carrying out chemical processes

2. Central vacuole: large organelle that stores proteins, pigments, and waste

3. Vesicles: small transport sacs

4. Chromosomes: DNA tightly pack around proteins

5. Cytoskeleton: proteins supporting the shape and structure of a cell

A. The nucleus acts as the information center 1. Nucleus: large organelle holding genetic

information

2. Nucleolus: area in nucleus synthesis of ribosomal RNA

3. The nuclear envelope: membrane around nucleus

i. nuclear pores: holes in nuclear envelope that allow passage of RNA and proteins

4. Chromatin: DNA wrapped around proteins called histones to form chromosomes

i. chromatin

ii. nucleosomes

iii. histones

5. The nucleolus: Ribosomal subunit manufacturing

i. Ribosomes are made of rRNA and protein.

ii. These parts are synthesized in the nucleolus.

B. Ribosomes are the cell’s protein synthesis machinery 1. ribosomal RNA (rRNA): along with

proteins they form ribosomes which make or synthesize proteins

2. messenger RNA (mRNA): carries info from DNA to ribosome

3. transfer RNA (tRNA) : carries amino acids to ribosomes

IV. The Endomembrane System (4.4)

1. Endoplasmic Reticulum (ER): phospholipid bilayer w/ proteins makes this folded internal membrane w/ channels.

2. Cisternal space/Lumen: inner region of ER

A. The Rough ER is a site of protein synthesis 1. Rough ER: Rough b/c it is covered w/

ribosomes. Makes proteins.

2. Glycoproteins: Proteins w/ short carbohydrate chains.

1. Smooth ER (SER): network of enzymes that synthesize carbohydrates and lipids. Stores Ca2+Modify foreign substances so they are less toxic, liver. cells would have a long SER

B. Smooth ER has multiple roles

C. The Golgi apparatus sorts and packages proteins

1. Golgi body: flattened stack of membranes

2. Golgi apparatus: collection of Golgi bodies that collect, package and distribute molecules sometimes from ER. Cis entrance; leave through trans face in vesicles. Finally it synthesizes the cell wall.

3. Cisternae: stacked membrane that can pinch off to form vesicles for transport.

D. Lysosomes contain digestive enzymes

1. Lysosomes: membrane bound digestive vesicles that break down and recycle proteins, lipids, nucleic acids and carbohydrates.

1. Phagocytosis: Cells can take in large molecules of food in vesicles which fuse w/ lysosomes for digestion.

E. Microbodies: vesicles w/ enzymes

1. Peroxisomes: microbodies w/ digestive and detoxifying enzymes that produce and break down hydrogen peroxide and remove electrons.

2. Glyoxysome: microbody found in plants that convert fats to carbs.

F. Plants use vacuoles for storage and water balance

1. Vacuoles: Stores useful molecules like sugar, ions, pigments and water as well as waste.

The large central vacuole in plants allows the cell to contract and expand through water channels.

Different types of vacuoles exist.

2. Tonoplast: membrane around vacuole that contains water channels to maintain water levels.

V. Mitochondria and Chloroplasts: Cellular Generators

A. Mitochondria metabolize sugar to make ATP

1. Mitochondria: organelle involved in cellular respiration. It has its own DNA. They can divide to reproduce but this process is dependent upon DNA in the nucleus.

2. Cristae: inner membrane of mitochondria increasing surface area.

3. Matrix: solution in the interior of cristae involved in respiration

4. Intermembrane space: outer compartment of mitochondria.

5. ATP: energy storing molecule produced during cell respiration

B. Chloroplasts use light to generate ATP and sugars

1. Chloroplasts: organells that carry out photosynthesis. They make their own food thanks to Chlorophyll (green pigment). Consist of membrane, grana and own DNA.

2. Grana: stacked thylakoids

3. Thylakoids: closed sections of membrane containing photosynthetic pigments

4. Leucoplast: organelles that contain DNA but have no pigment.

5. Amyloplast: Leucoplast that stores starch (amylose)

6. Plastid: organelles that can reproduce and carry out photosynthesis or serve as storage

C. Mitochondria and chloroplast arose by endosymbiosis

Endosymbiosiseukaryotes derived from one prokaryote engulfing another

i. Inner membrane of mitoch and chloropl came from membrane of prokaryote, outer membrane from plasma membrane or ER of host.

ii. Mitoch are size of bacteria and inner membrane similar to folded membrane of bacteria.

iii. Ribosomes of mitoch and bacteria similar

iv. Mitoch and chloropl have circular DNA like prokaryotes

v. Genomes of mitoch and chloropl similar to bacteria

vi. Mitoch divide by fission like bacteria

VI. The Cytoskeleton: made of long protein fibers 3 types of fibers make

the cytoskeleton

1. Actin filaments: Actin subunits link to create long protein fibers made of 2 protein chains twisted together. Responsible for contractions, crawling, pinching off, and cell extensions.

2. Microtubules: tubulin subunits link to make protein filaments form a tube shape. Help in intracellular transport and separation of chromosomes.

3. Intermediate filaments: proteins overlapping, twisted and bundled together for strength. Protein subunits include vimentin for stability. Examples of intermediate filaments are keratin found in our hair and fingernails and neurofilaments found in nerve cells.

B. Centrosomes are microtubule-organizing centers

1. Centrioles: organelles made of 9 triplets of microtubules and involved in organization of microtubules during cell division (animal cells only). Make cytoskeletons, cilia and flagella.

2. Centrosome: area where pair of centrioles is found.

C. The cytoskeleton helps move materials within cells • Thin actin filaments and thick microtubules

coordinate activities like cell division.

• Actin and myosin are proteins involved in muscle movement.

• Anchors structures.

• Vesicle holding material is bound to a motor protein (kinesin) that uses ATP by a connector protein (kinectin or dynein).

• Microtubules act as a rail road track for these transport vesicles.

1. Molecular Motors

VII. Extracellular Structures and Cell Movement

A. Some cells crawl • Actin filaments quickly polymerize extending

part of the plasma membrane forward.

• Myosin proteins contract pulling the rest of the cell forward as well.

B. Flagella and cilia movement 1. 9 + 2 structure: 9 microtubule pairs

around 2 central microtubules

• Side arms are made of dynein, a protein motor molecule that changes using ATP

2. Basal body: 9 triplets of microtubules connected by proteins.

3. Cilia: short projections off a cell. There are usually many cilia for movement. They have a 9 + 2 arrangement of microtubules.

C. Plant cell walls provide protection and support

1. Primary walls: laid out when cell still growing

2. Middle lamella: sticky substance to glue cells together

3. Secondary walls: thick support and protection

D. Animal cells secrete an extracellular matrix • Animal cells secrete glycoproteins,

elastins, and collagen to form an extracellular matrix (ECM) around the cell.

• This ECM is bound to integrins which help hold the cytoskeleton in place.

• The ECM provides support and strength.