2.1.1 Cell Structure

How to prepare a light microscope

Staining and sectioning

What does staining do

Allows the specimen to become visible (chemical stains binds to on or in specimen)

E.g

• See certain (named) organelles

• Improves contrast

What are the different stains that bind to specific cell structures

Acetic orcein stains DNA dark red

Eosin stains cytoplasm pink

Sudan black stains membranes and other lipids black

What does sectioning do

Makes thin sections which allow the light to pass through

What problems can happen because of sectioning

Artefacts

Why do we use light microscopes

To look at whole cells and tissues

What organelles can you see with a light microscope

Nucleus

Mitochondria

Chloroplast

Cell membrane

Cell wall

What does TEM stand for

Transmission Electron Microscope

How does a transmission electron microscope work

Electron beam passed Through the specimen

Why does the specimen need to be thin when using a TEM

Specimen = thin to prevent deflection of electrons

Why do we use TEM’s

To look at organelles in detail

What organelles can you see with an electron microscope

Mitochondria

Golgi apparatus

ER

Lysosomes

Why do some TEM images appear different from each other

The mitochondria have been cut along different planes/ angles

What does SEM stand for

Scanning Electron Microscope

How does a scanning electron microscope work

The beam of electrons scans the surface of the specimen

The reflected beam is detected

The detector and the source are on the same side of the specimen

Why do we use SEM’s

To look at the cell surface

How to remember Laser Scanning Confocal microscope

Liesel Sees Colour

How does the Laser Scanning Confocal microscope work

Specimen treated with fluorescent dye

The laser focuses on this causing the dye to be seen

Facts about Laser Scanning Confocal Microscope

Very thin specimen needed

High resolution

Used to find eye problems

Why do we use Laser Scanning Confocal microscope

To look at an object at a certain depth within the cell

(e.g cytoskeleton in the cell)

Magnification definition

The number of times larger the image is in comparison to the object

(20x means 20 times larger)

Resolution definition

The ability to distinguish between two points as sperate entities

The ability to distinguish between very small structures that are close together in detail

Light microscope magnification and resolution

Up to x1500 (magnification)

50-200 nm (max resolving power)

TEM magnification and resolution

up to 500,000 (magnification)

0.05-1nm (max resolving power)

SEM magnification and resolution

Up to 100,000 (magnification)

0.20nm (max resolving power)

How to go from cm to mm to μm to nm

cm x10 → mm x1000 → μm x1000 → nm

How to go from cm to mm to μm to nm image

μm meaning

Micrometers

What two pieces of equipment do you need to calibrate a microscope

Eyepiece graticule

Stage micrometer

calibrating video

…

Marks for drawing from a microscope image

Use up to half the page

Clear and continuous lines (not ragged and broken) and no shading

Proportions correct

Label

Rule the label lines in pencil and don’t cross them

Label lines touch part that you’re labeling (no arrow heads)

Annotations

Scale

Title

What is the magnification formula

Magnification = Image over actual

(IAM)

Hard IAM question

If you have a scale bar and you need to find the actual size of the specimen

Measure length with ruler for Image size

Then measure length of scale bar of and convert to nano/ micrometers then sub into the IAM to find the magnification which is the length of scale bar measured with a ruler divided by the actual scale bar, then that’s the magnification

What is a nucleus

Nucleus controls nearly all the activities of the cell.

Contains DNA (genetic info) which controls the genetic code for proteins

What’s the difference between the nucleus and the nucleolus

Nucleolus has dense DNA

Nucleus is whole thing (Chromatin, nuclear envelope and pores)

What do the nuclear pores do

Allow substances in and out the nucleus, like mRNA leaving

What is the Rough Endoplasmic Reticulum (structure)

Flattened membrane bound sacs called cisternae.

Continuous with the nuclear envelope

RER has ribosomes on it

What happened at the rough ER

Protein synthesis

What is the Smooth Endoplasmic Reticulum (structure)

Flattened membrane bound sacs called cisternae.

Continuous with the nuclear envelope

Smooth ER has NO ribosomes

What happened at the smooth ER

Lipid and hormone production

What is the Golgi apparatus

A stack of membrane-bound flattened sacs

What happens at the Golgi apparatus

It modifies and packages proteins into vesicles

Some of these vesicles may be secreted out of the cell

What is the Ribosome

Tiny organelles, (in cytoplasm and on RER)

What happens at the Ribosomes

Site of protein synthesis

Where mRNA assembles proteins from amino acids

What is the mitochondria structure

Have 2 membranes separated by a fluid filled space.

The membrane is highly folded cristae

Central part = matrix

What happens at the mitochondria

ATP (adenosine triphosphate) is made during aerobic respiration

What is the lysosome structure

Spherical sacs surrounded by membrane

What happens at the lysosome

Contains powerful digestive enzymes

(break down materials)(used a lot in wbc)

Where is the chloroplast and its structure

Found only in plant cells

2 membranes separated by a fluid filled space

Inner membrane = continuous with a network of flattened disks called thylakoid (where chlorophyll is found)

A stack of thylakoids = a granum (plural grana)

What happens at the chloroplast

The site of photosynthesis, which is driven by light energy

What is the plasma/ cell surface membrane made from

Made out of phospholipid bilayer

What happens at the plasma/ cell surface membrane

Controls what goes in and out of the cell

What are centrioles

Small tubes of protein fibers, a pair of then found next to nucleus in an animal cells

What do centrioles do

Take part in mitosis to form spindle fibres

What is the cell wall

Plant cells = made of cellulose

Bacteria cells = made of peptidoglycan

What is the qualities of the cell wall

Provides high tensile strength

Insoluble

Inert

What is the flagella structure & where

Found in procaryotes

Have 9 + 2 arrangement

What does the flagella do

Causes whole cell to move

Powered by chemiosmosis

What is the cilia

Finger like appendages on ciliated epithelial cells

What happens at the cilia

They move substances along

(mucus in the trachea)

What is the vacuole structure

Membrane bound organelle found in plant cells

Membrane surrounding vacuole = tonoplast

Filled with water and enzymes

What happens at the vacuole

Removes unwanted substances from the cell and alters the cell shape by changing the amount of water in the vacuole (turgid or flaccid)

What is the vesicle

A membranes bound organelle

What does the vesicle do

Transports substances

What is found in a plant cell but not an animal cell

Centrioles

Glycogen granules

(Lysosomes)

(Cilia)

(Flagella)

What is the interrelationship between the organelles

To produce a protein (enzyme..) or hormone in that cell

(simple) Protein synthesis

Nucleus produces mRNA

mRNA leaves the nuclus through the nuclear pore

mRNA attaches to a ribosome

• Either free in the cytoplasm or bound to an RER

Once protein made through protein synthesis, it goes ito a vesicle an dis transported to the golgi apparatus.

At the Golgi apparatus/ body, the protein is modified (adding carbohydrates..) and packded into a vesicle again

Vesicle moved to cell surface membrane of a eukaryotic cell = exocytosis occurs

mitochondira - produces atp = needed for contractile filimaents in the cytoskeleton

Cytoskeleton - made of contractile filaments which need atp to move vesicles from the golgi body, to the cell surface membrane to allow exocytosis to occor

What are the 3 main components of the cytoskeleton

Microfilaments

Microtubules

Intermediate filaments

Importance of the cytoskeleton

Whole cell support

Movements of cilia and flagella

Changing cell shape

Moving organelles (like a vesicle)

Movement of chromosomes

What does the cytoskeleton need

Cytoskeleton needs ATP - made through aerobic respiration in mitochondria

Because they are contractile filaments

What is a microfilament

6nm

Made of actin

Contract and are used in cytoskeleton

Importance of microfilaments

Changes in cell shape

Microtubules

25nm

Made of globular tublin proteins form tubes

Importance of microtubules

Moves chromosomes in mitosis (forming spindle)

Acts as tracks for organelles to move along

Moves organelles around the cell e.g vesicles

Intermediate filaments

10nm

Actin and microtubules

Importance of Intermediate filaments

Gives mechanical strength to cells, whole support

Importance of the flagella

(only in prokaryotes)

Movement of whole organism

By using ATP

using a motor

Importance of the cilia

Found in Eukaryotic cells

(esophagus, nasal cavity)

Movement of substances

Difference between prokaryotic and eukaryotic cells

Eukaryotic - membrane bound organelles and nucleus

PRo - no membrane bound organells an dno nucleus

Cell wall (capsule) of a Prokaryotic cell

Made of murein or peptidoglycan

High tensile strength

Cell surafce or plalsma membrane of a Prokaryotic cell

Allows substances in and out of the cell

Only membrane

Cytoplasm of a Prokaryotic cell

Site of chemcial reactions

Ribosomes of a Prokaryotic cell

Site of protein synthesis

70s

Size of ribosome in a eukaryotic cell

80s

Plasmids in a Prokaryotic cell

Circular DNA

Can be passed to other bacteria to exchange genetic info

(through pili to other surrounding bacteria - if pili tehere)

Pili in a Prokaryotic cell

Used for lateral flow of DNA to other bacteria

Nucleioud in a Prokaryotic cell

Circular DNA (eukaryotes have linear)

Genetic info

(not all have this)

Bacterial flagellum in a Prokaryotic cell

Used to move the cell

Needs ATP

Where is DNA found in a Prokaryotic cell

Plasmids or in Nucleoid - no nucleus

Where is ATP made in a Prokaryotic cell

Mesosome - in folded regions of the cell membrane

Prokaryotes and Eukaryotes link

Chloroplasts and mitochondria have evolved from prokaryotes

internal structure = similar

DNA found is circular and smaller ribosomes (70s not 80s)