Cell structure ALL

What is cell theory?

• all living organisms consist of cells

• cells are formed by division of pre-existing cells

• cells contain DNA that acts as instructions for growth

How long do temporary mounts last?

A few hours

How are permanent specimens prepared for microscopy?

• specimen is dehydrated 

• fixed in wax

• thinly sliced

How are dry mounts prepared?

• solid specimens can be viewed as a whole

• or cut into very thin slices (sectioning)

• placed on slide and covered with a coverslip

How are wet mount prepared?

• specimens suspended in liquid

• coverslip placed at an angle to avoid bubbles

• eg, aquatic life, living organisms

How are squash slides prepared?

• wet mount prepared and coverslip pressed on

• sample is squashed between two slides

How are smear slides prepared?

• edge of slide used to smear a sample along another 

• coverslip then placed on top 

• eg. blood slide

What is the purpose of staining samples in microscopy?

Provides contrast - different components within a cell take up stains to different degrees

How is magnification calculated?

Image size ÷ actual size

What do positively charged dyes stain?

Cell components 

What do negatively charged dyes stain?

Stain outside of the cells - the background

Why use a differential stain?

• provides contrast

• only some organelles take up stain

Why is gram staining used?

Separates bacteria into two groups:

• gram positive 

• gram negative

What is the definition of magnification?

the number of times larger an image is compared with the real size of the object

What is the definition of resolution?

the ability to distinguish between two separate points

What are the two types of electron microscopes?

1. Transmission electron microscope 

2. Scanning electron microscope 

How does a transmission electron microscope work (+ magnification and resolution)?

• beam of electrons passes through the sample

• electrons are detected by a sensor

• imaged is 2D

• magnification x500 000

• resolution = 0.5nm

How does a scanning electron microscope work (+ magnification and resolution)?

• scans the surfaces of the sample

• electrons are reflected

• sensor detects electrons and an image is created

• produces a 3D image

• magnification x500 000

• resolution = 3-10nm 

How does a light microscope work (+ magnification and resolution)?

• specimen can be viewed whilst still alive

• can be stained to add contrast

• color can be seen

• light is shone through specimen then passes through two lenses

• lenses magnify the image

• magnification x1500

• resolution = 200nm

What are the disadvantages of electron microscopes?

• only produce black and white images 

• specimen must be in a vacuum - must not be living 

• specimen must be dehydrated

• very expensive 

• very large

What is an artifact?

a visible structural detail caused by processing the specimen and is not a feature of the specimen eg. air bubbles trapped under a slide when using a light microscope

What is an eyepiece graticule?

• small ruler that is inserted into the eyepiece of a microscope

• scale is arbitrary

• the eyepiece graticule remains constant at all magnifications

• must be calibrated using a stage micrometer

What is a stage micrometer?

• used to calibrate eyepiece graticule 

• it is 1cm long and is divided into 100 division 

• 1 division = 100 micrometers 

What type of organelles do prokaryotic cells contain?

They contain only non-membrane bound organelles.

How do prokaryotic cells store their genetic information?

As a single looped chromosome in cytoplasm

What is the size of a prokaryotic cell compared to a eukaryotic cell?

Much smaller (1-10 micrometers vs 10-100)

Are prokaryotes typically multi or uni-cellular?

Typically uni-cellular

How do prokaryotic cells divide?

Binary fission

Describe the structure of the nucleus

Largest organelle, surrounded by double membrane called nuclear envelope

What is the function of the nucleus?

Contains genetic material, makes RNA and ribosomes, controls the cell's activities

Describe the structure of the mitochondria

Surrounded by double membrane, inner membrane folded to form cristae. Contains DNA and ribosomes.

What is the function of mitochondria?

Site of aerobic respiration and produces ATP

Describe the structure of the rough endoplasmic reticulum

Flattened membrane sacs called cisternae with ribosomes attached

What is the function of the rough ER?

Site of protein synthesis and then transports proteins

Describe the structure of the smooth ER

Flattened membrane sacs called cisternae NO RIBOSOMES

What is the function of the smooth ER?

Lipid and steroid synthesis

Describe the structure of the golgi apparatus

Stack of membrane bound sacs

What is the function of the golgi apparatus?

Modifies proteins (adding sugar or lipid molecules) and folding proteins into 3D shapes. Packages proteins into vesicles for transport.

What are vesicles?

Membrane sacs used to transport materials

Describe the structure of a chloroplast

Surrounded by a double membrane with a highly folded inner membrane embedded with chlorophyll. Also contain DNA and ribosomes

Describe the structure of the inside of a chloroplast

Contains a matrix of stroma which has a system of membranes running through it. These are stacked in places to form grana (contain chlorophyll). Stroma contains circular DNA, ribosomes and starch grains.

What is the function of the chloroplast?

Site of photosynthesis

Describe the structure of a lysosome

Spherical sacs containing powerful digestive enzymes

What is the function of a lysosome?

Destroys worn out organelles and digests the contents of vacuoles formed by phagocytosis

Describe the structure of a vacuole

Bound by a single membrane called a tonoplast. Contains cell sap.

What are the main components of cell sap?

Mineral salts, pigments, organic acids and other substances.

What is the function of a vacuole?

Stores waste products and cell sap. Changes in volume affect turgidity of the cell.

Describe the structure of a ribosome

Not membrane bound. Made of protein and RNA

What is the function of a ribosome?

Protein synthesis

Describe the structure of a centriole

Made of two bundles of protein. Each cylinder made up of nine fibres.

What is the function of a centriole?

Form spindle fibres and are involved in formation cilia and flagella.

Describe the structure of a cell wall

Made of cellulose and is fully permeable

What is the function of a cell wall?

Provides mechanical support and protection. Prevents cell from bursting.

What are the functions of the cytoskeleton?

Establishes cell shape, provide mechanical strength, locomotion, chromosome separation in mitosis and meiosis, movement of organelles within a cell

What are the 3 components of the cell cytoskeleton?

Microtubules, microfilaments and intermediate fibres

What is the size and function of microtubules?

25nm in diameter. Globular tubulin proteins polymerise to form tubes. Involved in transport of organelles. Make up the spindle fibres during cell division. 

What is the size and function of microfillaments?

7nm in diameter. Contractile fibres formed from the protein actin. Responsible for cell movement and cell contraction during cytokinesis. 

What is the size and function of intermediate fibres?

8-10nm in diameter. Give mechanical strength to cells and help maintain their integrity.

What are undulipodia and cilia + what are they made up of?

Hair like extensions that stick out from the surface of cells. Made of 9 pairs of microtubules in a circle w/ two more in the middle (9+2 arrangement)

What are the functions of undulipodia and cilia?

Move liquid past the surface of the cell. For single cells this enables them to swim. For anchored cells this moves liquid over the surface of the cell. 

What are flagella made of + where are they present?

Only present in bacterial cells. Made of a spiral of flagellin protein attached by a hook to a protein disc than can rotate. 

What is an advantage of being a eukaryote?

Organelles allow for division of labour. Each organelle is specialised to carry out a specific role.