Cells

Which of the following is/are properties of life?

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1. A) a complex organization

2. B) the ability to take in energy and use it

3. C) the ability to respond to stimuli from the environment

4. D) the ability to reproduce

5. E) All of the choices are correct.

A compound

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4% 4%0%0%

93%1. A) is a pure element.

2. B) is less common than a pure element.

3. C) contains two or more elements in a fixed ratio.

4. D) is exemplified by sodium.

5. E) is a solution.

All living things are made of cells

• Cells are the basic unit of living things

• All cells come from other cells

• This is the classical cell theory

Developments in the microscope facilitated development of Cell theory The drawings of Robert Hooke A dramatization of Antony

van Leeuwenhoek

Microscope power is limited by the wavelength of light used

• Visible light, 400-700nm in wavelength, is a small part of the electromagnetic spectrum

Light is a wave

2 waves can add to each other, or cancel each other out

• When waves are in phase, they are added together

• When waves are out of phase, they cancel each other out

Advances in microscopy continue to further knowledge of cells

• Electron microscopy allows far greater magnification than light microscopy

• Electron wavelengths are far shorter than those of visible light

Transmission Electron Microscope

• Very thin sections are made of a sample

• A beam of electrons is passed through the sample

• “Electron-dense” material in sample appears darker

Scanning Electron Microscope

• A thin film of gold is sprayed onto the surface of a specimen

• Electrons are reflected off surface

• Gives images 3-D appearance

Phase contrast microscope

• Speed of light slows down as light passes through a medium

• Wavelengths out of phase with each other will cancel out and appear darker

• Allows viewing live specimens without staining

Fluorescent microscopy

Cells are small

• Most bacteria are .5-2µm in size

• Light microscope’s limit= ~500nm=.5µm

• Single eukaryotic cells are larger, but still to small to see without magnification

Cells are small for good reason• Surface area:

volume ratio• Rate of

food/oxygen entering the cell depends on surface area

• For large volumes, this rate would approach zero

How do you think nerve and

muscle cells manage their

size?

• Turn to your neighbor and discuss this question.

Required for all cells:

• A genome• Separation of inside from outside• Means of obtaining energy• Means of utilizing energy• Protection

All living things can be placed into three domains

• Based on DNA evidence, all multicellular life is put into a single group, the eukaryotes

• Unicellular, prokaryotic life split into Eubacteria & Archaea

Cells can be placed into two categories

• Prokaryotic and eukaryotic

• Prokaryotic- smaller and simpler

• Eukaryotic- larger and more complex

• Eukaryotic- containing membrane-bound organelles

• Eukaryotes- “you”

Prokaryotic cells are smaller and simpler

• Archaebacteria and Eubacacteria are both prokaryotic

• Pro= before• Karyo= “kernel”

(nucleus)• The prokaryotic

genome is a circular piece of DNA

Cell structures common to most prokaryotes

• Flagellum• Ribosomes• Pili• Cell wall• Cell membrane (plasma

membrane)• Cytoplasm• Most structures found

in prokaryotes are also found in eukaryotes

The Cell Membrane is a flexible envelope for all cells

• Often made of a phospholipid bilayer• All substances entering or exiting cell must pass• To be discussed in detail in subsequent chapter

The Cell Membrane is a dynamic fluid mosaic

Receptor proteins, transport proteins, cholesterol, and the phospholipid bilayer

The cell membrane works for:

• Containment• Transport• Communication• Attachment

Ribosomes are the site of protein manufacture

• DNA blueprint is converted to mRNA

• At the ribosome, the mRNA is converted into protein

• Ribosomes are slightly different in eukaryotes, but the function is the same

Ribosomes convert RNA instructions into protein

Eukaryotic cells contain membrane-bound organelles

Eukaryotes can be unicellular or multicellular

Protists- mostly unicellular eukaryotes

Animals, plants, fungi- mostly multicellular eukaryotes

The cells of plants and animals are different

The nucleus contains the cell’s DNA

The endomembrane system is contiguous with the nuclear

membrane• Proteins fated for

export will be made on rough ER surface ribosome

• Membrane bound proteins are also sent here

• Ribosomes are also suspended in cytosol for synthesis of cytosolic proteins

The smooth ER plays a role in lipid synthesis and postranslational

modification of proteins• ER: endoplasmic

reticulum• Rough ER: with

ribosomes on it• Translation: turning

mRNA protein• Addition of sugars/

lipids to the surface of a protein can aid or change its function

The Golgi apparatus does further postranslational modification

• Other modifications can serve as address labels• Also key in the synthesis of lysosomes

Lysosomes are vesicles that contain digestive enzymes

• The pH inside a lysosome is different from the pH of the cytosol

• Lysosomes can be fused to food

LE 4-10a-1

Plasmamembrane

Rough ER

Lysosomes

Transport vesicle(containing inactivehydrolytic enzymes)

Golgiapparatus

LE 4-10a-2

Plasmamembrane

Rough ER

Lysosomes

Transport vesicle(containing inactivehydrolytic enzymes)

Golgiapparatus

Engulfmentof particle

“Food”

Foodvacuole

Digestion

LE 4-10a-3

Plasmamembrane

Rough ER

Lysosomes

Transport vesicle(containing inactivehydrolytic enzymes)

Golgiapparatus

Engulfmentof particle

“Food”

Foodvacuole

Digestion

Lysosomeengulfingdamagedorganelle

The nucleoid region of a prokaryotic cell

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1. A) contains the cell's DNA.

2. B) separates the RNA from the cytoplasm.

3. C) is surrounded by a nucleoid membrane.

4. D) contains the cell's nucleoli.

5. E) is the site of organelle production.

Pulse-chase experiments can demonstrate paths through endomembrane system

• Add normal cells to a “pulse” medium containing a radioactively labelled nutrient- 14C - leucine

• “Chase” with normal media

• Take samples of the cells every 10 min or so

• Cover samples with photographic emulsion and view

The mitochondrion breaks down nutrients to provide energy for cells

• 100’s of mitochondria in a single cell

• Site of cellular respiration• ATP is provided to the cell• They can decide a cell’s

time to die• They have their own DNA• Celluar respiration:

C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l) + energy

Plant cells have some distinctive organelles absent in cells of animals

• A large central vacuole is common in plants

• In plants, it is for storage of:

• water, sugars and acids, toxins, flower pigments,

• Provides shape

Vacuoles are not exclusive to plants

Plant cell walls are mostly composed of sugars

Section of a pine board

3 nm

Polymerized glucose- cellulose

Chloroplasts feed the world

• The organelle capable of performing photosynthesis:

• 6CO2(g)+ 6H2O(l) + hν C6H12O6(s) + 6O2(g)

• They contain chlorophyll , a green pigment which captures light

• They also contain their own DNA

Why do you think chloroplasts and mitochondria have their own DNA?

Turn to a neighbor and discuss this question.

Why do chloroplasts and mitochondria have their own DNA?

• Mitochondrial genes are similar to those of α-proteobacteria

• The endosymbiosis between mitochondria and eukaryotic cells appears to have a single origin

• In humans, 95% of mitochondrial genes are in the nucleus

• Scientists are less sure of a single origin for chloroplasts

• The lineage of plastids has become a field of study unto itself

• Includes secondary endosymbioses

• And tertiary ones• Chloroplast genomes

have widely disparate sizes

Chloroplasts also appear to have a

single origin

The Cytoskeleton• Actin microfilaments are contractile• Intermediate filaments provide shape• Microtubules help cells divide and provide highways

on which vesicles can travel• Vesicles- small membrane bound containers

Cytoskeleton elements work together in eukaryotic cilia and flagella

Motor proteins literally walk on microtubules

• Kinesin- plus-end directed

• Dynein- minus-end directed

• Both can carry vesicles• http://video.google.co

m/videosearch?q=kinesin&hl=en&emb=0#

Junctions in plants allow cells to share cytoplasm

• Can contain nutrients or chemical signals

• Viral infections also can spread through these junctions

Junctions in animal cells can make tissues water-tight

• Anchors and tight junctions are found in the blood-brain barrier

• Gap junctions allow cell to cell communication as plasmodesmata in plants

A cell is exposed to a substance that prevents it from dividing. The cell becomes larger and

larger. This situation

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20% 20% 20%20%20%1. A) should present no problem to the cell since it can continue to perform all other necessary functions.

2. B) should present no problem to the cell because the surface area of the cell will increase as the volume of the cell increases.

3. C) will eventually be problematic since the cell's ability to absorb nutrients through its outer membrane will not keep increasing as quickly as its cytoplasmic needs.

4. D) should be beneficial- the cell will be able to divert the ATP normally used for cell division to other processes.

5. E) None of the choices are correct.