cell structure

Resolution

The ability to distinguish between two objects very close together

Magnification

The number of times larger an image is than the real size of the object

What determines resolution?

The range of electromagnetic radiations of different wavelengths

Short wavelength…..________ resolving power

Higher

Why do light microscopes have a lower resolving power?

Longer wavelength

Three microscope?

light microscope, electron and scanning microscope

What sign is used for magnification

X

How is resolution measured

nm

What determines resolution?

Electromagnetic spectrum, shorter wavelength = higher resolving power

Why does the light microscope have a lower resolution?

wavelength of visible light is longer than of an electron, the ability to distinguish between two points is lower

Max resolution

Shortest distance between 2 seperate points

How to calculate max resolution?

½ wavelength

Wavelength of visible light

400-700nm

Mx resolution of light microscope

200nm

What happens is a spectrum is smaller then 20nm in a light microscope?

Points cannot be distinguished as seperate

Can ribosomes be seen under a light microscope?

25nm, so no, it is smaller then 20nm

Light microscope electromagnetic radiation

Visible light

Energy and wavelength of light microscope

Low energy and long wavelength

Highest magnification of light microscope

x1500

Advantage of light microscope

Live specimens can be viewed, image can be coloured

Source of electromagnetic radiation of electron microscope

Free electrons

Wavelength of electron microscope

1 nm

Energy and wavelength of electron microscope

High energy, very short wavelength

Key condition of electron microscope

Must be in a vacuum environment so electrons can travel in straight lines

Highest magnification of electron microscopes

x250,000

Max resolution of electron microscope

0.5nm

Disadvantage of electron microscope

Only dead material is viewed, images are black and white

2 types of electron microscopes

Transmission and scanning

Appearance of TEM

2D

Details inside cells of TEM

internal structures, membranes within internal structures

Scanning electrons microscope appearance

3D

Resolution of SEM compared to TEM

lower

Image length units

mm

How many graticule units are in the eyepiece graticule usually

100

Steps to measuring cells

1. Calibrate the eyepiece graticule with the stage micrometer

1 EPG = how many divisions = how many micrometers

2. Use the eyepiece graticule to measure cell/structure

1 cell = how many eyepiece graticule units = how many micrometers

Stage micrometer is usually in which units

mm

2 types of cells

Prokaryotes and eukaryotes

3 examples of eukaryotics

Plants, fungi and animals

Prokaryotes examples

Archaea, bacteria

Cell surface membrane how thick?

7nm

Cell membrane another name?

Plasma membrane

Appearance of cell surface membrane and why

Trilaminar appearance due to phospholipid bilayer

Function of cell surface membrane

Controls the exchange of materials between cells and their environments

Nucleus how many membranes?

2

Is nucleus the largest organelle?

Yes!

Functions of nucleus

Contains genetic information for the synthesis of protein, sit if transcription of genes and production of mRNA, DNA is protected from degradation by enzymes

What’s the outer layer of the nucleus? Function?

Nuclear envelope - attached to ER, 2 membranes, nucleus pores

Function: controls the movement of substances between nucleus and cytoplasm

Nuclear pores function

allow and controls the exchange between proteins and nucleotides in and mRNA, tRNA and ribosomes out between the nucleus and the cytoplasm

Nucleolus function

Dentist region, function is the site of ribosomal RNA synthesis, site of ribosome assembly

Function of chromatin

DNA and its associated proteins, they collect to form chromosomes during nuclear division

Are ribosomes bound by a membrane?

No

Facts about ribosome

Made of rRNA, that is synthesised in nucleolus + some protein, made up of subunits.

Function of ribosomes

Site of protein synthesis

Which are the two types of ribosomes?

80S and 70S

About 80S ribosomes

25nm, larger, found in cytoplasm and RER of all eukaryotes

About 70S ribosomes

18nm, smaller, found in mitochondria, chloroplasts and all prokaryotes

About RER

Extensive, connected system of membranes, made of cisternae, continuous with the nuclear envelope, running through cytoplasm, 80S ribosomes are attached

What is cisternae

Flattened membrane sacs

Function of RER

Site of protein synthesis, protein transport to golgi, protein modification (folding)

About SER

Continuous with RER, no ribosomes

Function for SER

Site of lipid and steroid synthesis e.g. cholesterol, steroid hormones, storage site for calcium ions

About Golgi body

Golgi apparatus, made of cisternae, layered appearance, no connection between membranes, not continuous with nuclear envelope, swellings at the end of saves for vesicle formation

Golgi body, being formed by..

Transport vesicles from RER on cis face

Golgi body broken down to form…

form secretory vesicles and lysosomes on trans face

Function for Golgi body

Modification of proteins and lipids e.g. glycosylation, phosphorylation = addition of phosphate go to protein cutting

Packaging molecules into vesicles for transport

Formation of secretory vesicles for release of protein out of cell

Formation of lysosomes

List of cell structures involved in the production and secretion of proteins, list in order

Synthesis of protein at ribosomes /RER

Transport vesicle buds off RER and fuses with the Golgi body

Modification of protein at Golgi body

Separation of a secretory vesicles form the Golgi body

Fusion of the vesicle with the cell surface membrane

Contents are released by exocytosis

About lysosomes

Very very small, spherical small sacs, single membrane, found in eukaryotes

Function of lysosomes

Contains hydrolytic enzymes / lysozymes, breakdown unwanted structures (worn out organelles or dead cells) via hydrolysis in an acidic environment, in WBC lysozymes digest bacteria

About Golgi vesicles

Small fluid filled sac found in cytoplasm, produced by Golgi apparatus, surrounded by a single membrane

Function of Golgi vesicle

Stores lipids and proteins made by Golgi apparatus and transports them out of the cell through the cell membrane by exocytosis

About mitochondria

large organelle, has double membranes, cristae, matrix, contains 70S ribosomes and small circular DNA

What’s cristae and where is it found

Mitochondria, folded inner membrane

What’s a matrix and where is it found

Mitochondria, interior solution

DNA in mitochondria

Small circular

Mitochondria origin?

Prokaryotic origin, hypothesised that they were able to synthesise their own energy in the form of ATP

Function of mitochondria

Site of aerobic respiration, synthesize ATP / produce energy in the form of ATP, release energy

Why are mitochondria shaped so differently

One is longitudinal cross section and the other is a transverse cross section

About chloroplasts

Large organelle second to nucleus, oval shaped, two membranes, contain chlorophyll, thylakoid, grand, stroma, contains 70S ribosomes, small circular DNA and starch grains, divides by binary fission (like mitochondria), has prokaryotic origin

Thylakoid

Flattened membrane sacs

Grand

Thylakoid sacs

Stroma

Interior solution

Function of chloroplasts

Site of photosynthesis (Light dependent reaction where light energy is absorbed and water is used to synthesise ATP), (Light independent reaction, ATP used to convert CO2 into glucose)

Photosynthesis equation

6CO2 + 12H2O -light + green plants→ C6H12O2 + 6O2 + 6H2O

About cell wall

Thick, rigid layer, made of cellulose, fully permeable : spaces and gaps between fibres

Function of cell wall

Provides structural support, prevents bursting by osmosis, limits cell size (prevents it from changing shape)

About Plasmodesmata

Strands of cytoplasm passing through channels

Function of plasmodesmata

Allows substances to pass, from cell to cell, without passing through cells walls e.g. water, sucrose, amino acids, mineral ions, ATP, allows a rapid transport of substances

About Vacuoles and tonoplast

Found in plant cells, large, permanent and central, surrounded by a partially permeable membrane called tonoplast

Function of vacuole

Stores cell sap (water, ions, minerals, salts, sugars, pigments), stores waste products, pushes chloroplasts to the edge of the cell giving turgidity to the cell

Protoplasm

All living parts of the cell

About centrioles

Cylindrical, made of 9 groups of 3 microtubules, NOT FOUND IN PLANT CELLS

Functions of centrioles

Involved in cell division (replicates before each cell division and moves to opposite poles), centrioles are found in pairs at right angles from each other, forms centrosome, modified centrioles are found elsewhere in flagellation and cilia, organises and assembles microtubules

What are centrosomes

It is a MTOC (microtubule organising centre)

Function of centrosome

Organises and assembles microtubules for the formation of spindle fibres at opposing poles during mitosis / cell division

About microtubules

Very small 25nm, made from tubulin (protein), form dimmers, dimmers polymerise to form long protofilaments, 13 protofilaments equal 1 microtubule, found in eukaryotic cells, formed and broken down by MTOC

Function of microtubules

Make up cytoskeleton, provides mechanical support, acts as an intracellular transport system for movement of vesicles or other components, make up spindle fibres and centrioles used in cell division, involved in the besting movements of cilia and flagella

About cilia

Found in eukaryotes, smaller in diameter then microfilm, motile, moves rhythmically, complicated structure made of microtubles

Structure of cilia

2 central microtubules with a range of nine microtubules doublets around the outside, each one have an A microtubule (ring of 13 protofilaments) and B microtubule (10 protofilaments attached to A), each A microtubule has 2 rows containing several hundred inner and outer arms made of the protein dynein, this protein connects with B microtubules of microtubule doublets to facilitate movement.

Function of cilia

For movement/locomotion (ciliated epithelial cells in lungs)

About microvilli

Only found in ANIMAL CELLS, found on epithelial cells in the intestines and kidneys, finger like extensions of the cell surface membrane