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.

role of coenzymes in enzyme-catalysed reactions?

Act as substrates for the enzyme

How is the production of mRNA in the eukaryote different from a prokaryote?

In eukaryote

Pre-MRA produced

Splicing

introns removed

Transport of carbohydrates

Sucrose actively transported into phloem

By companion cells

Lowers water potential

Produces higher hydrostatic pressure

Mass flow to respiring cells

Unloaded by active transport

Functions of bile salts

Emulsify lipids

Increase surface area for lipase activity

Form micelles

Describe how you would do cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue.

Homogenise to break open cells

Filter to remove debris

Cold solution to prevent enzyme activity

Solution with equivalent water potential to prevent osmosis

Buffet solution to stop enzymes denaturing

Centrifuge at a Lower speed so nuclei move to the bottom

Role of single stranded dna fragments

Templates

Determines order of nucleotides

Why is ATP a suitable energy source to use

Releases relatively small amount of energy

Releases energy instantaneously

Furoate are the compounds making them more reactive

Can be rapidly synthesised

Is not loss from cells

Describe the roles of calcium ions and ATP in the contraction of a microfibril

Calcium ions diffuse into myofibrosis from reticulum

Calcium ions cause movement of tropomyosin

Exposure of binding sites on the actin

Has attached a binding sites on actin

Hydrolysis of ATP causes myosin heads to bend

Pulling Acton molecules

Attachment of a new ACP molecule to each mycin head causes mycin heads to attach

Describe the part played by the inner membrane of the mitochondria in producing ATP

Electrons transferred down electron transport chain

Provides energy to take protons into space between membrane

Protons passed back through membrane through ATPAse

Energy used to combine ADP and phosphate to produce ATP

Why is it important that catalase can break down hydrogen peroxide quickly

breakdown of hydrogen

peroxide / H2O2 , minimises /

prevents, damage (to cells) ✓

products of breakdown are,

harmless / water and oxygen

Why is a cooling system necessary in fermentation

temperature affects , rate of

growth / enzyme activity ✓

(fungal) metabolic reactions

generate heat ✓

to inhibit growth of pathogenic

bacteria

How does the lactic acid extend the shelf life of yoghurt

pH below optimum ✓

(for) bacterial enzymes

How could hydrogen peroxide affect the plasma membrane

oxidises / reacts with / AW ,

fatty acids / phospholipids /

cholesterol ✓

damages / denatures (named)

, membrane proteins ✓

disrupts phospholipid bilayer ✓

causes membrane to be more

permeable

Cell surface membrane functions

barrier between cell

(contents) and environment ✓

regulates which substances ,

enter / leave , the cell

site of (chemical) reactions ✓

cell communication / cell

signalling

If a cell that completed the cell clue had more chromosomes than its normal diploid number,what checkpoint failed to work?

M

because...

chromosomes cannot have been,

aligned correctly at the equator /

attached correctly to the spindle

Observations if the cell had stopped dividing at the G2 checkpoint

larger number of (named) organelles ✓

more DNA / larger nucleus ✓

no visible chromosomes ✓

nuclear membrane present

DNA replication v transcription

Similarities

• DNA unwinds and unzips

• Helicase enzymes

• Template DNA

• Complementary base pairing

• Hydrogen bonds

• Free, activated nucleotides

• Polymerase enzymes

Differences

• Only a small section of DNA (where the

gene is located) unzips during

transcription

• Both strands act as templates in

replication

• RNA vs DNA free nucleotides

• RNA vs DNA polymerase

• Different helicase enzymes

• Products are two new daughter strands

of DNA in replication and one mRNA

strand in transcription

• mRNA leaves nucleus whereas the new

DNA strand remains bound to the

template strand

Why is tubulin essential to protein synthesis and secretion in eukaryotic cells?

mechanical strength (to cells) ✓

cell, support / stability /

maintains shape ✓

movement of (named),

molecules / vesicles / organelles

within cell

formation / movement, of, cilia /

flagella ✓

cell movement / endocytosis /

exocytosis / phagocytosis /

cytokinesis / described

holds organelles in position

DNA extraction

1. Break open cells (lysis)
   

   • Use: Detergent

   • Why: Detergent dissolves the cell membrane and nuclear membrane (phospholipid bilayers), releasing DNA.

3. Remove proteins
   

   • Use: Protease enzyme

   • Why: Protease breaks down proteins (e.g., histones) that DNA is wrapped around.

5. Filter the mixture
   

   • Use: Filter paper

   • Why: Removes large cell debris, leaving DNA dissolved in the liquid.

7. Precipitate the DNA
   

   • Use: Ice-cold ethanol (or isopropanol)

   • Why: DNA is insoluble in cold alcohol, so it clumps together and becomes visible as a white precipitate.

Role of membrane in rough ER

compartmentalisation / maintain different

conditions from cell cytoplasm

separating proteins (synthesised) from cell cytoplasm ✓

3 hold, ribosomes/ enzymes, in

place

Function of the cytoskeleton

provides mechanical strength to

the cell ✓

2 holds organelles in place ✓

aids transport of, (named)

molecules / (named) organelles

(within the cell) ✓

4 cell movement ✓

5 maintains cell, shape / structure

/ integrity / stability

cell division /

Cleavage in cytokinesis / spindle fibres

Function of helicase

Unzips double helix

Breaks h bonds between two strands

How to prepare a blood smear that could then be stained and viewed under a microscope

use pipette to place

blood on slide ✓

2. (place blood) near

one end (of slide) ✓

use (2nd) slide / cover

3.

slip , to spread / AW ,

blood across slide ✓

4. slide / cover slip , at

an angle

How could different objective lenses of a light microscope be used to focus and observe the pond water sample at high power magnification

select low power lens

then higher power ✓

use coarse focus to

2

find, correct field of

view / object

use fine focus for

clear(er) image ✓

ref to x4 / x10 / x40

4

(lens power /

magnification)

How would an image look if a cell was in interphase?

single area of dark (staining

material) ✓

(individual) chromosomes not

visible ✓

(nuclear material) not as dark

Method in chromatography that will separate amino acids in collagen

1 digest / hydrolyse / break down,

collagen into amino acids ✓

and

2 place, sample / AW, on,

chromatography paper /

chromatography plate / stationary

phase ✓

3 dry and repeat ✓

4 place, (chromatography) paper /

(chromatography) plate/

stationary phase, in solvent

why is collagen such a strong molecule

many H bonds

many covalent bonds

polypeptides overlap

how can conc of a reducing sugar be measured using a colorimeter?

1.use standard conc

2.heat with Benedicts solution

3.use same vol of solution

4.use excess Benedict

5.changes to green/yellow/brick red

6.remove ppt/obtain filtrate

7.calibrate/0 colorimeter

8.using a blank/water/unreacted Benedicts

9.use red filter

10.reading of absorbance

11.more transmission=more sugar present

12.calibration curve

13.plot absorbance against sugar conc

13.use reading of unknown and read off graph

what bond is broken in the hydrolysis of a phospholipid molecule

ester

can Hb change shape

yes

how do R groups interact to determine the tertiary structure of a protein

some R groups attract/repel

disulfide bridges between cysteine

H bonds/ionic bonds

lipids:animals v plants

saturated

no double bonds

solid at room temp

roles of lipids

thermal insulation

energy store

protection

membranes

steroid hormones

buoyancy

waterproofing

source of water

production of fat soluable

similarities:collagen v Hb

amino acid chain sequence

peptide bonds

helix

3 bonds

quaternary structure

more than one polypeptide

functions of alpha glucose

respiratory substance

source of energy

formation of ATP

glycogen v cellulose

how do LDLs affect the formation of atheromas

carry cholesterol from liver to tissue

receptors on cells

raise blood cholesterol

increase deposition of fats

form plaques

how do HDLs affect the formation of atheromas

carry cholesterol from tissues to liver

receptors on liver cells

lower blood cholesterol

reduce deposition of fats

form plaques

molecules that combine with cholesterol to form LDLs

saturated fats

protein

where are H bonds found in biological molecules

protein secondary structure

protein tertiary structure

between polypeptide chains in quaternary structure

between chains of cellulose

between strands in DNA

how does a peptide bond form

condensation reaction between amine group of one amino acid and carboxyl group

H from amine combines with OH from carboxyl

structure of collagen

peptide bonds between amino acids

every 3rd amino acid is glycine

coil

left-handed helix

3 polypeptide chains

H bonds between chains

cross-links

fibril

Hb v collagen

Hb:

globular

hydrophobic inside,hydrophilic outside

4 chains

2 alpha subunits,2 beta subunits

describe how a substrate,such as pepsin,breaks down a substrate

substrate shape is complementary to active site

substrate fits into active site

induced fit forms ESC

destabilising bonds in substrate forms enzyme-product complex

products leave active site

how would repeating an experiment improve it?

improves reliability

assesses variability

mean can be calculated

anomalous results can be indentified

how do cells move through their environment?

flagella,cilia,shortening and lengthening of actin filaments

how might the lipid content of mycoprotein differ from food that comes from animals

less overall lipid/fat

less saturated fat

more unsaturated fat

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