All bio mols so far

what happens before a cell divides?

each chromosome makes an identical copy of itself so that the daughter cell will contain exactly the same DNA as the parent cell

how is a template formed for DNA replication?

the two strands of the double helix separate and each strand acts as a template for the formation of a new strand

what is semi conservative DNA replication?

when DNA replicates, 2 new molecules are produced, each consisting of one original strand and one new strand

what are the two new molecules like in semi conservative replication

the two new molecules are identical to each other and to the original DNA parent molecule

what separates the 2 strands of DNA by breaking the hydrogen bonds between the bases?

• DNA helicase

what does the enzyme DNA helicase do?

• it breaks the hydrogen bonds between the complimentary bases, separating the 2 strands of DNA

• (unzips DNA)

What does the enzyme RNA primase do?

• synthesises very short sections of RNA complementary to the relevant exposed bases

• this acts as a starting point for the enzyme DNA polymerase

what does the enzyme DNA polymerase do?

joins up the sugar phosphate backbone

What happens during the joining stage of DNA replication?

Free nucleotides line up with the exposed bases on each strand, and the enzyme DNA polymerase joins the nucleotides together to form the new DNA strands

which way can DNA polymerase move along the DNA?

it can only move along the DNA in the 3’ to 5’ direction

what is the name of the strand which can be replicated continuously and which way does it go?

• leading strand

• 5’ to 3’

what is the name of the strand which is replicated discontinuously and is what direction?

• the lagging strand

• 3’ to 5’

what are the fragments called that DNA is replicated in on the lagging strand?

Okasaki fragments

what seals the Okasaki fragments together?

the enzyme DNA ligase

why is there one discontinuous/lagging strand in DNA replication?

the enzyme DNA polymerase can only work 3’ to 5’ and as the strands are antiparallel it means there is one continuous strand and the other is discontinuous as it works as it unwinds

how are mutations formed?

• when random errors occur in DNA replication, it leads to a change in the sequence bases

what were the 3 alternative models for DNA replication that were suggested?

• conservative

• semi-conservative

• dispersive

what is the conservative method of replication?

• suggested that parental DNA strands remain together and newly formed daughter strands are also together

what is the dispersive method of replication?

• suggested that after replication the 2 daughter DNAs had alternating segments of both parental and newly synthesised DNA interspersed on both strands

what were the scientists called who did an experiment to discover which DNA model of replication were correct - and what year?

• Meselsohn and Stahl

• 1958

what was the aim of Meselson and Stahl’s experiment?

to determine which model of DNA replication is correct

what bacteria did Meselson and Stahl use?

E. coli

what was Meselson and Stahl’s method?

• Bacteria were grown in a medium containing heavy nitrogen (¹⁵N)

• DNA became labelled and heavy

• Bacteria were transferred to a medium containing light nitrogen (¹⁴N)

• DNA was extracted after each round of replication

• DNA was separated by centrifugation based on density

what were Meselson and Stahl’s results after one replication?

• One intermediate band was observed

• Conservative replication was ruled out because it would produce two bands (one heavy parental DNA and one light new DNA)

what were Meselson and Stahl’s results after 2 replications?

• Two bands were observed: one light and one intermediate

• Dispersive replication was ruled out because it would produce only one band, which would become progressively lighter after each replication, not two distinct bands

• Results supported semi-conservative replication

• This model predicts one hybrid molecule after first replication and a mixture of hybrid and light DNA after second replication

• Each new DNA molecule contains one original strand and one newly synthesised strand

what were Meselson and Stahl’s conclusion?

• DNA replication is semi-conservative

• Each daughter DNA molecule contains one original strand and one newly synthesised strand

how does the structure of RNA differ from DNA?

• the pentose is ribose not deoxyribose

• there is no thymine; uracil is present instead and binds to adenine

• it is single stranded not double

• it is shorter than DNA with a lower molecular mass

what are 3 types of RNA?

• ribosomal RNA

• messenger RNA (mRNA)

• transfer RNA (tRNA)

what is messenger RNA (mRNA)?

• single polynucleotide strand formed in the nucleus during transcription, using a specific section of the DNA molecule (gene) as a template

• carries a copy of the genetic info of the gene to the ribosomes in the cytoplasm

• mRNA is used in translation to determine the sequence of amino acids in a protein (it’s primary structure)

what is transfer RNA (tRNA)?

• tRNA molecule is a single strand folded into a clover leaf shape

• different types of tRNA molecule in the cytoplasm, each with a binding site for the attachment of a specific amino acid

• during protein synthesis each tRNA molecule carries its specific amino acid to a ribosome

• a specific sequence of three bases on the molecule is known as an anticodon

what is central dogma?

describes the flow of genetic information from DNA to RNA to protein, outlining the processes of transcription and translation.

what is a gene?

a section of DNA that codes for a particular protein

what is a triplet code?

• 3 bases code for 1 amino acid (4^3 different combinations = 64) - for 20 amino acids

how does transcription occur?

DNA on the template strand is converted into a complementary sequence

how does translation occur?

• the sequence of bases in mRNA determine the order of amino acids in the polypeptide chain

• tRNA molecules bring the amino acids to the mRNA in the right order

where does transcription occur?

inside the nucleus

where does translation occur?

in the cytoplasm (attached to a ribosome)

what are nucleic acids?

large molecules which make up the genetic material of all living things

are nucleotides monomers or polymers?

polymers

what monomers make up nucleic acids?

nucleotides

what are 2 examples of nucleic acids?

• DNA

• RNA

what are 3 differences between DNA and RNA?

• DNA is has a deoxyribose sugar, RNA has a ribose sugar

• DNA has Thymine (T), RNA has Uracil (U)

• DNA has 2 polynucleotide strands, RNA has 1 polynucleotide strand

what 3 parts is a nucleotide made up of?

• pentose sugar (deoxyribose for DNA, ribose for RNA)

• phosphate group

• nitrogenous base

what is the structure of ribose?

5 carbon sugar (pentose) with the molecular formula C5H10O5, existing in both linear and ring forms

how are individual nucleotides formed?

condensation reactions between components

how are nucleotides linked to form polymers?

• the phosphate of one nucleotide can join to the sugar of another

what bond is formed between 2 nucleotides?

a phosphodiester bond

what type of reaction is it when nucleotides join?

a condensation reaction

what is formed when many nucleotides join together?

• polynucleotide chain or nucleic acid

• they from a sugar-phosphate backbone, with the bases protruding to the side

which bases have a single carbon ring, and which bases have a double carbon ring in their molecular structure?

• Cytosine and Thymine are single carbon ring

• Guanine and Adenine are double carbon rings

which bases are complementary to each other?

• A - T

• C - G

what is the structure of DNA?

• DNA forms a double helix

• DNA is double stranded - made up of 2 strands of polynucleotides held together by H bonds between the bases

• Each strand has a phosphate group (5’) at one end and a hydroxyl group (3’) at the other end. The two strands are arranged that they run in opposite directions - said to be antiparallel

what is the term to describe how the strands in DNA run in opposite directions to each other?

• the strands are antiparallel

what does the term antiparallel mean in DNA?

• the two strands in DNA run the opposite way to each other

is it 3’ or 5’ strand if the phosphate group is the one sticking out on the end?

5’

is it 3’ or 5’ strand if the sugar group is the one sticking out on the end?

3’

is RNA single or double stranded?

single

what are the 5 nitrogenous bases?

• adenine

• thymine (not present in RNA)

• cytosine

• guanine

• uracil (only present in RNA)

what are the 2 groups the nitrogenous bases can be sorted into?

• purines

• pyrimidines

what are pyrimidines?

they contain a single carbon ring

what are purines?

they contain a double carbon ring

what is the difference between pyrimidines and purines?

pyrimidines have a single carbon ring whereas purines have a double carbon ring

what are some purines?

• adenine

• guanine

what are some pyrimidines?

• thymine

• cytosine

• uracil

do purines always bond with another purine or a pyrimidine?

• purines always bond with a pyrimidine

• pyrimidines always bond with purines

• this happens in their complimentary pairs

how many H bonds is there between adenine and thymine?

2 H bonds

how many H bonds are there between guanine and cytosine?

3 H bonds

what is ATP?

• an energy carrying molecule released in respiration

• it is a phosphorylated nucleotide - this means that it is a nucleotide with a phosphate group added

what is a phosphorylated nucleotide and what is an example of one?

• a nucleotide with phosphate groups added

• e.g. ATP

what does DNA stand for?

deoxyribonucleic acid

what is the method for extracting DNA and why do you do each step?

1. Mash up strawberries → breaks up cell walls/increase in surface area

2. Add extraction liquid including detergent, salt and protease

3. Then filter → removes insoluble structures, filtrate contains dissolved DNA

4. Add ice cold ethanol → precipitates out DNA strands and makes them visible

Properties of water

• Polar

• High boiling point

• High specific heat capacity

• Less dense in solid state

• Cohesive properties

• Adhesive properties

• Not easily compressed

What does polar mean?

There is an uneven distribution of electrons in a molecule, resulting in an uneven charge across the molecule.

In a water molecule what are the slight charges on the oxygen and hydrogen atoms?

Oxygen = slightly negative 

Hydrogen = slight positive

What is a hydrogen bond?

The weak interaction between a slightly negatively charged atom of a molecule and a slightly positively charged atom on another molecule.

How strong is a hydrogen bond?

Hydrogen bonds are relatively weak (weaker than a covalent bond)

Why is water a good solvent?

Water is polar, so any other polar molecule will dissolve very easily

Why is water a transport medium for living organisms?

It is an excellent solvent - minerals and ion dissolve very easily

Why does water have a high boiling point?

• Contains many hydrogen bonds

• Requires lots of energy to break the hydrogen bonds

• Therefore is a good coolant

Why does water have a high specific heat capacity?

Many hydrogen bonds require lots of energy to overcome

Why is ice less dense than water?

• When water is cooled below 4 degrees maximum number of hydrogen bonds form

• Bonds fix molecule in an open lattice structure

• Molecules are held further apart than in the liquid state

Why does water have adhesive and cohesive properties?

It is polar

Why is it important for life that water has a high specific heat capacity?

Temperature remains fairly constant - provides a stable environment (in cells and for aquatic organisms)

Why is it important for life that water has a high boiling point?

It is a good coolant 

Why is it important for life that water is more dense than ice?

• Ice floats

• Water below is insulated

• Aquatic animals do not freeze and currents can move

What does water’s cohesive properties create?

Surface tension

Why is cohesion necessary for water to act as a transport medium?

• Water is attracted to other polar surfaces 

• Allow for capillary action 

• eg. in xylem of plants 

what is chromatography?

• a method of separating components of a solution based on differences in solubility

what phases does chromatography use?

• a stationary phase (paper or thin gel)

• a mobile phase (a solvent that moves up the stationary phase, carrying the components of a solution with it)

what is amino acid chromatography?

• a mixture if amino acids can be separated by chromatography

• to visualise the amino acids on the paper, the chromatogram needs to be sprayed with Ninhydrin

how do we use Rf values to identify amino acids?

• the distance moved by each amino acid relative to teg distance moved by the solvent is called the rf value

• different amino acids have specific rf values, so this method can be used to separate and identify amino acids

What elements are carbohydrates made up of?

• Carbon

• Hydrogen

• Oxygen

Examples of monosaccharides

• Glucose

• Fructose

• Galactose

• Ribose

• Deoxyribose

Disaccharides

• Lactose 

• Maltose 

• Sucrose 

Which monosaccharides is lactose made up of?

Glucose + galactose 

Which monosaccharides is maltose made up of?

Glucose + glucose

Which monosaccharides is sucrose made up of?

Glucose + fructose

Polysaccharides 

• Starch 

• Glycogen 

• Cellulose 

What is starch made of?

Alpha glucose molecules

What is glycogen made of?

Alpha glucose molecules