Comprehensive A-Level Biology: Cell Structure, Function, and Microscopy Techniques

What is resolution?

The minimum distance between two objects where they can still be viewed as separate.The minimum distance is determined by the wavelength of light in a light microscope and the wavelength of the electron beam in an electron microscope.

how do cells move through their environment?

flagella,cilia,shortening and lengthening of actin filaments

connective tissue

holds other types of tissue together

what effect will inhibiting RNA polymerase have on protein synthesis?

phosphodiesther bonds cannot form between adjacent nucleotides

no translation

difference between template and coding strand in transcription

mRNA strand has a sequence of bases complementary to the template strand

coding strand determines the amino acid sequence

when extracting DNA,how could damage to DNA by enzymes be reduced?

lower temperature to inhibit enzyme

why would it be difficult to calculate a valid mitotic index from an image even if a higher magnification is used

cells may be damaged

not stained enough

layer of cells overlap

fields of view

why does mitotic index not fully explain overall growth

only gives info about cell divison

cells increase in size during growth

growth is a combo of cell division and increase in size

what technique was used to determine the double-helical structure of DNA?

X-ray crystallography

functions of glycoproteins

Cell recognition

Receptors

Antigens

Cell adhesion

Cell signalling

saturated fatty acids

triglycerides containing 3 of them are normally solid at room temperature

can pack closely together

bond that holds alpha glucose and fructose together

1-6 glycosidic bond

How is magnification calculated?

Magnification = size of the image / size of the real object.

What type of microscope uses a beam of electrons to create an image?

Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM).

What is the purpose of calibrating a microscope?

To align the stage micrometer and eyepiece graticule for accurate measurement.

What is the scale of a typical eyepiece graticule?

The scale is usually 1mm long with 100 divisions, so each division is 10μm.

What should you do when drawing a specimen under a microscope?

Draw in pencil, title the diagram, and state the magnification used.

What is a technique that uses different chemical stains to color various parts of a cell?

Staining technique.Acetic orsin binds to DNA and stains chromosomes dark red.Eosin stains cytoplasm.Sudan red stains lipids.Iodine in potassium iodide solution stains the cellulose in plant cells yellow and starch granules blue.

How are permanently fixed slides made?

Dehydrate the specimen.Embed the wax to prevent distortion during slicing.Cut them into very thin slices.

How does a Transmission Electron Microscope (TEM) work?

The specimen has to be chemically fixed by being dehydrated.A beam of electrons passes through the sample,which is stained with metal salts, to create an image, focused using electromagnets in a vacuum.

What are the advantages of using a TEM?

Highest resolving power and high magnification.

What are the disadvantages of using a TEM?

Requires extremely thin specimens, complex staining methods, and the specimen must be dead.

What can you see with a TEM?

A 2D image of details within organelles, such as cristae in mitochondria and grana in chloroplasts.

What does a Scanning Electron Microscope (SEM) provide?

A 3D image of the surface of cells and organelles with a magnification from x15 to x200,000.

What are the advantages of using a SEM?

High magnification and the ability to view 3D images.

What are the disadvantages of using a SEM?

Requires extremely thin specimens, complex staining methods, and the specimen must be dead.

What is the role of electromagnets in electron microscopy?

They are used to focus the beam of electrons onto the sample.

What is the significance of using a vacuum in electron microscopy?

A vacuum is required to prevent electron scattering by air molecules.

What is the difference between a light microscope and an electron microscope?

Light microscopes use visible light to magnify specimens, while electron microscopes use electron beams for higher resolution.

metaphase 1

individual chromsomes assemble on the metaphase plate

independent assortment to produce genetic variation

which processes require a membrane:diffusion,active transport,osmosis

active transport,osmosis

what is the function of phospholipids in a cell membrane?

to make a cell membrane more flexible

What is the main limitation of light microscopes compared to electron microscopes?

Light microscopes have lower resolving power due to the longer wavelength of light.

What is the function of a stage micrometer?

It is a microscope slide with a ruler/scaled bar etched into it for calibration purposes.

What is the structure of the plasma membrane?

A phospholipid bilayer with embedded intrinsic and extrinsic proteins.

What surrounds the nucleus?

A double membrane called the nuclear envelope with nuclear pores.

What are functions of the nucleus?

The control centre of the cell

Stores the organism's genome

Transmits genetic information

Provides the instructions for protein synthesis

What is contained within the nucleus?

Chromosomes with proteins bound, linear DNA, and a nucleolus.

What is the function of the nucleolus?

To synthesize ribosomes.It has no membrane and contains RNA

What is chromatin?

Chromatin is the genetic material,consisting of DNA wound around histone proteins.When the cell is not dividing,chromatin is spread out or extended.When the cell is about to divide,chromosomes condenses and coils tightly into chromosomes.These make up nearly all the organism's genome.

What occurs at the site of transcription in the nucleus?

Primary mRNA splicing.

What is the role of nuclear pores?

To allow movement of substances to and from the cytoplasm.

What are cilia?

Hair-like projections out of cells that can be mobile or stationary.

What is the function of mobile cilia?

To help move substances in a sweeping motion.

What is the structure of mitochondria?

Double membrane with inner membrane folded into cristae and a fluid-filled center called the matrix.2-5 micrometres long.

What is the primary function of mitochondria?

Site of ATP during aerobic respiration.Self-replicating

What is the structure of flagella?

Whip-like structures made of microtubules that occur in pairs.

What is the function of flagella?

For mobility,and sometimes as a sensory organ for chemical stimuli.

What is the structure of a centriole?

made of microtubules and occur in pairs to form a centrosome

What is the function of a centriole?

Involved in the production of

spindle fibre and organisation of

chromosomes in cell division

What is the Golgi apparatus made of?

1 membrane bound,Stacks of membranes creating flattened sacs called cisternae, surrounded by vesicles.

How many bases make one genetic code?

4^3=64

Experiment to support semi- conservative replication

Meselson and Stahl experiment on bacteria

DNA v RNA

deoxyribose v ribose

thymine v uracil

2 polynucleotides v 1 polynucleotide

What is the glycocalyx?

Portion of glycolipids and glycoproteins form an extensive sugary coat called glycolayx. Act like a molecular signal that enables cells to recognize on another.

What is the smooth endoplasmic reticulum (SER)?

A system of membranes with no bound ribosomes.

What is the role of potassium ions in cells?

Stomatal opening and nerve impulse transmission.

What is the function of hydrogen ions in cells?

Chemiosmosis, pH regulation, and translocation.

What type of bonds provide stability and rigidity to cell walls?

Large number of hydrogen bonds between chains.

What is the function of the Golgi apparatus?

To modify proteins by:

Adding sugar molecules to make glycoproteins

Adding lipid molecules to make lipoproteins

Being folded into 3D shapes.

The proteins are packaged into vesicles that are pinched off and then:

Stored into cell

Moved to the plasma membrane

What is the structure of lysosomes?

Vesicles formed from the Golgi apparatus containing hydrolytic enzymes.

What is the function of lysosomes?

To hydrolyze pathogens and cell waste products.

What is the cytoskeleton?

A network of fibers found within the cytoplasm, consisting of rod-like microfilaments made of actin, straight and cylindrical microtubules, and intermediate filaments .

What are the functions of microfilaments?

Responsible for cell movement.

What are the functions of microtubules?

Responsible for creating a scaffold-like structure and providing mechanical strength.They from the track along which motor proteins walk and drag organelles from one part of the cell to another.They form the spindle before a cell divides.These spindle threads enable chromosomes to be moved within the cell.They make up the cilia,flagellum and centrioles.

What are the functions of the intermediate filaments?

They anchor the nucleus within the cytoplasm.They extend between cells in some tissues,between special junctions,enabling cell-to-cell signalling and allowing cells to adhere to a basement membrane,therefore stabilising tissue.k

What is the rough endoplasmic reticulum (RER)?

A system of membranes with bound ribosomes, often continuous with the nucleus.

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

It provides a large surface area for ribosomes, which assemble amino acids into proteins. These proteins then actively pass through the membrane into the cisternae and are transported to the Golgi apparatus for modification and packaging.

What are the properties of amylose?

It is coiled to form a helix and joined via 1-4 glycosidic bonds.

What is the function of the RER?

Site of protein synthesis (translation).

What is the function of the SER?

To create, store, and transport lipids and carbohydrates.Catalyse reactions such as synthesis of cholesterol,synthesis of lipids/phospholipids needed by the cell and synthesis of steroid hormones.

What is the structure of a cell wall?

Made of polysaccharides; cellulose in plants, chitin in fungi, and peptidoglycan in bacteria.

Found in plants,algae and fungi

What is the function of the cell wall?

Provides structural strength and prevents cells from bursting due to osmotic pressure.

What is the structure of ribosomes?

Small organelles in cells made up

of protein and rRNA

Ribosomes are made up of a small

and large subunit (80S size in

eukaryotes)

What is the function of a ribosome?

Site of protein synthesis

Site of translation in protein

synthesis

What is the structure of a chloroplast?

Surrounded by a double membrane

Contains thylakoids, which are

folded membrane containing

pigments

Contains a fluid membrane: the

stroma

Organelles involved

in the secretion of

proteins

Polypeptide chains are synthesised in

the RER

These chains are packaged into

vesicles to be sent to the golgi

apparatus via the cytoskeleton where

they are to be modified

Then from the golgi they are packaged

into secretory vesicles carry the protein

to the cell membrane to be released via

exocytosis

Contrast

prokaryotic and

eukaryotic cells

Prokaryotic cells are smaller

Prokaryotes have no membrane-

bound organelles

Prokaryotes have smaller 70S

ribosomes

Prokaryotes have no nucleus-circular

DNA is not associated with histones

Prokaryotic cell wall made of

peptidoglycan instead of cellulose/

chitin

Possible extra

organelles of

prokaryotes

Plasmids:Loops of DNA found in prokaryotic cells.

Capsule surrounding the cell wall:

gives protection from the immune

system

Flagella: locomotion

What is the role of calcium ions in cells?

Muscle contraction and nerve impulse transmission.

What is the role of sodium ions in cells?

Co-transport and reabsorption of water in the kidney.

What is a triglyceride composed of?

One molecule of glycerol and three fatty acids.

What type of bonds are formed in triglycerides?

Three ester bonds.

Anions and their

Functions

Nitrate ions: absorbed by plants to

make amino acids and nucleotides

Hydrogencarbonate ions: carbon

dioxide transport

Chloride ions: carbon dioxide

transport

Phosphate ions: phospholipids,

nucleic acid, ATP

Hydroxide ions: pH

What type of bonds allow water molecules to stick together?

Hydrogen bonds

Properties of water

1.An important solvent in reactions

2.A transport medium

3.A coolant

4.Provides habitat

What is the role of water as a solvent?

Polar, or charged, molecules

dissolve readily in water due to

water being polar; that is, they are

hydrophilic

Non-polar molecules, such as

lipids, cannot dissolve in water;

that is, they are hydrophobic

What happens to the internal temperatures of plants and animals in fluctuating external temperatures?

They remain constant.

Water as a transport medium?

Cohesion:The sticking together of water molecules via hydrogen bonds.Forms a continuous column of

water in the xylem of plants

What is the structure of water?

Water contains one oxygen atom

bound to two hydrogen atoms

Water is polar due to uneven charge

distribution in the molecule

Oxygen has a slight negative charge

and the hydrogens have a slight

positive charge

How does water function as a coolant?

It has a high specific heat capacity and high latent heat of vaporization.This is due to the strong hydrogen

bonds (as there are many of them)

Internal temperatures of plants and

animals remain constant despite

external fluctuating temperatures

Provides a cooling effect via sweat.

Water as a habitat

Water buffers temperature

therefore provides a stable internal

environment

Cohesion provides surface tension

enabling small invertebrates to live

on water surfaces

Ice is less dense than water due to

the hydrogen bonds and so can

float, providing habita

Monomers

Small, single units that act as

building blocks to create larger

molecules

What is condensation in chemistry?

The joining of two smaller monomer units to form a chemical bond with the release of water.

What is hydrolysis?

The breaking of a chemical bond between two bonded monomers by adding a water molecule.

What are the structural isomers of glucose?

Alpha glucose and beta glucose.

What is the difference between alpha glucose and beta glucose?

In alpha glucose, the H group is at the top of the hexose ring on carbon 1; in beta glucose, the OH group is at the top.

What are disaccharides?

Carbohydrates formed from two monosaccharides joined by a glycosidic bond through a condensation reaction.

What is maltose?

A disaccharide formed from two alpha glucose molecules.

What is lactose?

A disaccharide formed from beta glucose and galactose.