Cell Structure

What is magnification?

How much bigger an image appears compared with the original object

What is resolution?

To produce an image with fine detail using a microscope

What is a light microscope?

* Uses visible light with a wavelength between 400-700nm
* Cheap, easy to use, portable and can study whole specimens

What is an electron microscope?

Use a beam of fast travelling electrons with a wavelength of 0.004nm electrons are fired from a cathode and focused by magnets onto a photographic plate/screen

What is a transmission electron microscope?

A beam of electrons is transmitted through a specimen and focused to produce a 2D black and white image -electron micrograph

What is a scanning electron microscope?

* Secondary electrons bounce off specimen's surface and focused on a screen
* 3D image black and white
* Magnification= X15-X200000

What is a laser scanning microscope?

Uses a laser to scan an object point by point to assemble a high resolution pixilated image

What is staining in terms of light microscopy?

Coloured chemicals that bind to molecules that make specimen visible

What is differential staining?

* Staining each structure differently
* acetic acid= binds to DNA stains chromosomes dark red
* eosin= stains cytoplasm
* sudan red= stains lipids
* Iodine in potassium iodide solution= stains cellulose in plant cell walls yellow and starch blue/black

How do you prepare specimens for staining?

* Dehydrate specimens
* Embed them in wax to prevent distortion during slicing
* Use a special instrument to cut slices thin

How do you observe unstained specimens?

* Some microscopes use light interference to produce a clear image
* some use dark backgrounds against illuminated specimen
* Useful for showing living specimens

What can you observe with a light microscope?

* Living organisms- Paramecium and Amoeba
* Smear preparations of human blood and cheek cells
* Thin sections of animal, plant and fungal tissue

What is an eyepiece graticule?

A measuring device placed in the eyepiece of a microscope and acts as a ruler when you view an object under the microscope

What is a stage micrometre?

Precise measuring device that is a small scale that is placed on a microscope stage and used to calibrate value of eyepiece divisions at different magnifications

How do you use a stage graticule to calibrate the eyepiece graticule?

1. Insert eyepiece graticule into X10 eyepiece of you microscope
2. Place stage micrometre on microscope stage and bring to focus
3. Align eyepiece graticule and stage micrometre and check the value of one eyepiece division at this magnification

What do all eukaryotes contain?

* Nucleus containing DNA
* Nucleolus containing RNA where chromosomes unwrap
* Cytoplasm
* Cytoskeleton- network of protein filaments within cytoplasm that move organelles from place to place within a cell allow some cells to move and muscle contraction
* Plasma membrane
* Membrane bound organelles
* Small vesicles
* Ribosomes

What are membrane bound organelles?

Organelles covered by a membrane keeping organelles separate from the rest of the cell only in Eukaryotic cells and electron microscopes have allowed 3D pictures of it

What is the structure of a nucleus?

* Surrounded by ==double membrane called nuclear envelope== which has pores
* ==Nucleolus contains RNA== no double membrane
* Chromatin is genetic material/DNA wound around histone proteins
* When cell ==not dividing=== chromatin ==spread out==
* When ==about to cell divide=== chromatin ==condenses and coils== into chromosomes

What is the function of the nucleus?

* Control centre of cell
* Stores organism’s genome
* Transmits genetic information
* Provides instructions for protein synthesis

What is the structure of the rough endoplasmic reticulum (RER)?

* System of membranes containing fluid filled cavities, cisternae, that are continuous with nuclear membrane
* Coated with ribosomes

What is the function of the RER?

* Intercellular transport system
* Cisternae form channels for transporting substances
* Provides large surface for ribosomes
* These assemble amino acids into proteins and pass through membrane to cisternae

What is the structure of the smooth endoplasmic reticulum (SER)?

* System of membranes containing cisternae that are continuous with nuclear membrane
* ==No ribosomes==

What is the function of the SER?

* Contains enzymes that catalyse reactions involved with lipid metabolism such as:
* Synthesis of cholesterol
* Synthesis of phospholipids/lipids
* Synthesis of steroid hormones
* Involved with absorption, synthesis and transport of lipids from the gut

What is the structure of the golgi apparatus?

* Stacks of membrane bound flattened sacs
* Secretory vesicles bring materials to and from Golgi

What is the function of the Golgi apparatus?

* ==Proteins are modified== by:
* Adding sugars to make glycoproteins
* Adding lipids to make lipoproteins
* Being folded into 3D shape
* ==Proteins then packaged into vesicles== which are:
* Stored in cell or moved to plasma membrane to be exported or incorporated into plasma membrane

What is the structure of the Mitochondria/ian?

* Spherical, rod shaped or branched 2-4um long
* Surrounded by 2 membranes with fluid filled space between them
* Inner membrane highly folded ==(cristae)==
* Inner part of mitochondria is ==fluid filled matrix==

What is the function of the Mitochondria/ian?

Site of ATP production during aerobic respiration

What is the structure of a Chloroplast?

* Large organelles 4-10um long
* %%Found only in plant cells%%
* Surrounded by double membrane or envelope
* Inner membrane continuous with stacks of flattened membrane sacs %%(thylakoids)%% these contain chlorophyll
* %%Each stack of thylakoids= granum%%
* %%Fluid filled matrix= stroma%%
* Chloroplasts contain loops of DNA and starch grains

What is the function of a Chloroplast?

* %%Site of photosynthesis%%
* 1st stage= light energy trapped by chlorophyll used to make ATP occurs in grana water split to supply hydrogen ions
* 2nd Stage= hydrogen reduces CO2 using ATP to make carbohydrates occur in stroma
* Abundant in in leaf cells particularly in palisade mesophyll layer

What is the structure of a vacuole?

Surrounded by a membrane called tonoplast and contains fluid

What is the function of the vacuole?

* %%Plant cells only have a permeant vacuole%%
* Filled with water and solutes and %%maintains cell stability%%
* When full makes cell turgid as pushes against walls

What is the structure of a lysosome?

* Small bags formed from Golgi surrounded by a single membrane
* ==Contain powerful hydrolytic (digestive) enzymes==
* Abundant in phagocytic cells

What is the function of a lysosome?

* Keep powerful hydrolytic enzymes separate from rest of cell
* Can ==engulf old cell organelles== and foreign matter return digested components to cell for reuse

What is the structure of Cilia and Flagellum?

* Protrusions from the cell and surrounded by cell surface membrane
* Contain microtubules
* Formed from centrioles

What is the function of Cilia and Flagellum?

* Epithelial cells lining airways have hundreds of cilia that move mucus
* Sperm have flagellum which enables them to move

What is the structure of a Ribosome?

* Small spherical organelles 20nm in diameter
* Made of ribosomal RNA
* Made in nucleolus as 2 separate subunits which pass through nuclear envelope into cytoplasm
* Some remain free in cytoplasm and some attach to endoplasmic reticulum

What is the function of a Ribosome?

* Bound to exterior of RER and ==synthesis proteins==
* Free in the cytoplasm either singly or in clusters and are site of protein assembly

What is the structure of a Centriole?

* Consist of 2 bundles of microtubules at right angles to each other
* Microtubules made from tubulin protein subunits and are arranged to form a cylinder

What is the function of a Centriole?

* Before a cell divides the spindle makes threads of tubulin that forms from the centriole
* Chromosomes attach to middle of spindle and motor proteins walk along tubulin threads pulling chromosomes to opposite ends of cell
* Centrioles involved in formation of cilia and flagellum

What is the structure of the Cytoskeleton?

* ==Network of protein structures== within the cytoplasm which consists of:
* Rod like ==microfilaments made from actin==
* Intermediate filaments 10nm in diameter
* Straight cylindrical microtubules made from tubulin 18-30nm in diameter
* The ==cytoskeletal motor proteins=== myosins, kinesins and dyneins are molecular motors
* They are also enzymes and have a site that ==binds to and allows hydrolysis of ATP==

What is the function of the Cytoskeleton?

* Protein microfilaments give ==support and mechanical strength==
* Microtubules provide shape and support to cells and help substances to move in cytoplasm
* Can form track motor proteins walk on
* Form spindles before a cell divides which allows chromosomes to be moved within the cell
* ==Intermediate filaments== anchor nucleus within cytoplasm and extend between cells in some tissues between special junctions ==enabling cell to cell signalling==

What is the structure of a Cellulose Cell Wall?

On the outside of the plasma membrane and made from bundles of cellulose fibres

What is the function of a Cellulose Cell Wall?

* ==Absent from animal cells==
* Prevent plant cells from bursting
* Provide strength and support
* Maintain cell shape
* Permeable so allow solutions to pass through

Label the 3 structures covered in a Nucleus

Top box= Nuclear envelope

Bottom box= Nucleolus

Far right box= Nucleus

Label the 3 structures covered in the Golgi

Black box= Cis face

Orange box= Cisternae

Yellow box= Trans face

Label the 2 structures covered in the RER

Black box= Cisternae

Orange box= Ribosomes

What kind of microscope was used to capture this electron micrograph of a nucleus?

Electron microscope

What kind of microscope was used to capture this electron micrograph of red blood cells?

Scanning electron microscope

What kind of microscope was used to capture this image of onion cells?

Light microscope

How are proteins formed and secreted?

* The gene that has coded instructions for the protein is ==transcribed into mRNA==
* mRNA is copied an ==pass out of pores in nuclear envelope== to the ribosomes
* At ribosomes instructions are ==translated== and molecule is assembled
* Molecule ==passes into cisternae of RER==
* ==Vesicles with the molecule are pinched off RER== and pass via microtubules and motor proteins to the ==Golgi==
* Vesicles ==fuse with Golgi where molecules may be modified== for release
* Inside vesicles pinched off from Golgi and ==pass into plasma membrane==
* Vesicles and plasma membrane ==fuse and molecule is released out of the cell==

How are Prokaryotes and Eukaryotes similar?

* Both have a plasma membrane
* Both have a cytoplasm
* Both have ribosomes
* Both contain DNA and RNA

How are Prokaryotes and Eukaryotes different?

* Prokaryotes much smaller
* Prokaryotes have less developed cytoskeleton with no centrioles
* Prokaryotes ==do not have a nucleus==
* Prokaryotes do not have membrane bound organelles
* Prokaryotes have a wall made of peptidoglycan

What features are individual to Prokaryotes?

* Have a protective waxy capsule surrounding their cell wall
* Small loops of DNA called ==plasmids==
* Have ==flagella== that enable them to move
* Have ==pili== smaller hair like cells that allow bacteria to adhere to host cells/each other

How do Prokaryotes divide?

Through binary fission where DNA is copied so each new cell receives large loop of DNA and plasmids