Biology 5 markers

Cell fractionation

Firstly, you need to homogenise the cell (break apart) the cell and this can be done in several ways such as grinding the cell in a blender or vibrating it, which breaks apart the plasma membane and releases the organelles into a solution

There are several conditions that the solution must be in.

-The solution must be kept ice cold to reduce the activity of enzymes that break down organelles.

-The solution should be kept isotonice which means it shoud have the same concentration of chemicals as the cells broken down to prevent damage of organelles through osmosis

a buffer solution should be applied to maintain ph

Next we do filtration, filtering the homogenised cell solution through a guaze to seperate cell debris or tissue debris.

Now we do the main bit, ultracentrifugation

The cell fragments are poured into a tube. This tube is poured into a tube which is put into a centrifuge that has been spun at a low speed.

The heavies organelles, like nuclei, get flung to the bottom of the tube and form a thick sediment known as the pellet. The rest of the organelles stay suspended in a fluid called the supernatant.

the supernatant is drained of and poured into another tube and spun at a higher speed. Again the heaviest organelles rise to the top. the process repeats until we get the organelles we want.

Order of heavy to least heavy

Nuclei, mitochondria, lysosomes, endoplasmic reticulum, ribosomes.

Water 5 marker

Water is an important metabolite and is used in a lot of chemical reactions like hydrolysis/ condensation

Water is a good solvent and chemical reactions happen quicker in solution

Water is cohesive - this is important for the transport of water in the xylem and for creating surface tension

Water has a high specific heat capacity which makes it a good temperature buffer

Water has a high specific latent heat of vaporisation which means it has a good cooling effect. eg. for sweat

Semi conservative DNA replication

DNA helicase breaks the hydrogen bonds between the complementary base pairs on the strands

Each strand acts as a template strand.

Free floating DNA nucleotides align with explosed base pairs on template strands via complementary base pairing

DNA polymerase joins together the adjacent DNA nucleotides via a condensation reaction producing a phosphodiester bond
Hydrogen bond reforms between the complimentary strands

This is called semi conservative replication. Each new dna molecule has one strand from the original dna molecule and one new strand.

How does the structure of DNA relate to its function?

Sugar phosphate backbone provides strength and stability

Large molecule so it can store lots of genetic information. The base sequence codes for amino acids

Helical/coiled which makes it compact

Double stranded so DNA replication can use both strands as template strands

Lots of hydrogen bonds provide strength yet there weakness alone can be broken for dna replication/ transcription

Name the steps of transcription

RNA polymerase attatches to the DNA double-helix at the begining of the gene. DNA helicase breaks the hydrogen bonds between the complementary base pairs in DNA.

One strand acts as a template strand

Free floating RNA nucleotides align with exposed bases on the template strand using complementary base pairing

Uracil replaces thymine

RNA polymerase joins adjacent RNA nucleotides forming phosphodiester bonds creating pre-MRNA

Pre-MRNA undergos splicing which removes introns, leaving the final mRNA molecule.

Name the steps of translation

mRNA leaves the nucleus and attatches to a ribosome.

.A tRNA molecule with a complementary anticodon binds to the first codon on mRNA using complementary base pairing

The tRNA molecule based on the triplet code brings a specific amino acid.

A second tRNA molecule binds to the second codon on mRNA, bringing a second specific amino acid

The two amino acids are joined by a peptide bond in a condensation reaction using energy from ATP hydrolysis

The first tRNA molecule detatches and leaves the ribosome

The ribosome moves along the mRNA and process continues until a STOP codon is reached, forming the polypeptide

Name the structure of cellulose

Cellulose is made of long unbranched chains of beta glucose.

Every second beta glucose molecule is inverted

When beta glucose molecules bond they form straight cellulose chains

The cellulose chains are linked together by many hydrogen bonds to form strong fibres called microfibrils which helps provides structural support for cells

Whats the difference between amylose and amylopectin

Amylose is a long unbranched chain of alpha glucose which is coiled, making it more compact as you can fit more into a small space.

Amylopectin is a long branched chain of alpha glucose whose side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily which means glucose can be released easily

Glycogen structure

has a very similar structure to glycogen. Its just that animals store glucose ans glycogen.

It has a lot more side branches than amylopectin which allows for more energy to be released quickly

it is also very compact which means its good for storage.

Natural selection

Within a population there is genetic variation due to random mutations in the base sequence of DNA

This means that some individuals will have an advantageous allele for their environment/ selection pressures

These individuals are more likely to survive and reproduce and pass on the advantageous allele to their offspring

Over many generations the frequency of the advantageous allele in the population increases.

Transmission electron microscopes pros and cons

Transmission electrons are good because they give high resolution images so you see the internal structure of organelles like chloroplast

However you can only use them on thin specimens

Scanning electron microscopes are good because they can be used on thick specimens but they give lower resolution images

they both do not produce things in colour.

Describe the stages of phagocytosis

Phagocytes identify foreign antigens and bind on to them.

This causes the phagocyte to engulf the cell forming a phagosome

The phagosome then fuses with the lysosome to form phagolysosomes

The lysosome contains digestive enzymes which hydrolyse the pathogen

The pathogen is broken down, its materials are absorbed and its antigens are presented while leftovers are released by exocytosis.

Describe HIV replication

The attatchement proteins bind to the complementary receptors on the T helper cells.

The RNA and reverse transcriptase enter the T helper cell

Reverse transcriptase makes DNA using the viral RNA

The vireal DNA is intergrated into the T helper cell DNA

Viral proteins are made

The virus is assembled and released from the cell. The T helper cell is destroyed

What is the difference between prokaryotic and eukaryotic dna

Eukaryotic DNA is long and linear whereas prokaryotic DNA is circular

Eukaryotic DNA is associated with the histone protein which tightly pack DNA allowing more to be stored in the nucleus, prokaryotic DNA is not associated with any protein

Eukaryotic DNA is found in the nucleus prokaryotic DNA is found in the cytoplasm

Eukaryotic DNA can be found in the mitochondria whereas Prokaryotic DNA cannot

Name the phases of mitosis

Interphase- the cell carries out the normal functions but the cell starts to divide

prophase- the chromosomes condense getting shorter and fatter. the bundles of protein called centrioles start moving to opposite ends of the cell forming a a network of protein across it called the spindle

the nuclear envelope breaks down and chromosomes lie free in the cytoplasm

metaphase- the chromosome each with two chromatids line up along the middle of the cell and become attatched to the spindle by their centromere

anaphase - the centromere divide, seperating each pair of sister chromatids. The spindles contract, pulling chromatids to opposite poles of the spindle, centromere first. this makes the chromatids appear v shaped

telophase - the chromatids reach the end of the poles and become long and thin again. they are now once again called chromosomes. a nuclear envelope reforms

cytokinesis takes place dividing the cytoplasm creating two identical daughter cells

Mitosis practical

cut 1cm from the tip of a growing root. it needs to be from the tip because thats where the growth occurs and where mitosis takes place

prepare a boiling tube containing 1M hydrochloric acid and put it in a water bath at 60C

transfer the root tip into the boiling tube and incubate for about 5 minutes

use a pipette to rinse the root tip with cold water. leave the tip to dry on a paper towel

Place the root tip on a microscope and cut 2mm from the very tip of it. Get rid of the rest.

use a mounted needle to break the tip open and spread the cell out thinly

Add a few drops of stain and leave it for a few minutes. The stains will make chromosomes easier to see under a microscope. There are loads of different stains all with different mass

Place a coverslip over the cells and push down firmly to squash the tissue.This will make the tissue thinner and allow light to pass through it. Don’t smear the coverslip sideways or you’ll break the chromosomes

Look at all the stages of mitosis under the optical microscope

Define Aerobic respiration

Glycolysis (cytoplasm)

Glucose is phosphorylated into glucose phosphate and then hexose biphosphate using ATP hydrolysis (the Pi). Hexose biphosphate (6C) splits into 2 molecules of triose phosphate (3C).

Each triose phosphate is oxidised to pyruvate and NAD is reduced to NADH, with synthesis of 2x ATP (from ADP and Pi) for each reaction

There is a net gain of 2x ATP in glycolysis

Line re

action (matrix of mitochondria)

Each Pyruvate (3C) is decarboxylated removing carbon and releasing carbon dioxide

Pyruvate is also oxidised to acetate (2C) and NAD is reduced

Coenzyme A (coA) is added to acetate to form acetyl coenzyme A (2C)

The Krebs Cycle

The Krebs cycle = tricarboxylic acid cycle = citric acid cycle

The Krebs cycle is a series of redox reactions each catalysed by an enzyme

Acetyl coA enters combines with a 4C compound to produce a 6C compound citrate. Coenzyme A is released and can go back to the link reaction

Per cycle 2x CO2 is produced

Per cycle 3x NADH and 1x FADH are produced

Per cycle 1x ATP is produced by substrate level phosphorylation

Oxidative phosphorylation

NADH and FADH are oxidised releasing a hydrogen which splits into protons and electrons

The electrons move down the electron transport chain proteins in a series of REDOX reactions, losing energy

The energy is used to pump protons from the matrix into the inter membrane space

This creates a H+ concentration gradient, so H+ diffuse back down into the matrix through ATP synthase

This provides energy to synthesise ATP from ADP

At the end of the electron transport chain the proton and electrons move down combines with oxygen to form water. Oxygen is the final electron acceptor