Unit 1.5 - Nucleic Acids and their functions Flashcards
Give 3 examples of Nucleic acids
Deoxyribonucleic acid
Ribonucleic acid
ATP
What are Deoxyribonucleic acid, Ribonucleic acid and ATP all?
Nucleic acids
What are all nucleic acids formed from?
Nucleotides
What to nucleotides form?
Nucleic acids
What’s the basic unit of nucleic acids?
Nucleotides
What are all the different sections on a nucleotide?
Phosphate
Organic base/nitrogenous base
Pentose sugar
What do Phosphate, Organic base/nitrogenous base and Pentose sugar all make up?
Nucleotides
Name of the base on a nucleotide
Organic or nitrogenous
What does ATP stand for?
Adenosine triphosphate
What’s the organic/nitrogenous base on ATP?
Adenine
What’s the Pentose sugar on ATP?
Ribose
What’s the phosphate on ATP?
Triphosphate (3 phosphate groups)
What type of bonds are between the phosphate groups on ATP?
High energy bonds
What are high energy bonds in ATP?
The bonds between the phosphate groups
What is adenine in ATP?
Organic/nitrogenous base
What is ribose in ATP?
Pentose sugar
Does ATP form polymers? (+explanation)
No - it’s a single nucleotide
What’s the only part of a nucleotide that has nitrogen atoms?
The base
What can vary with a nucleotide?
The organic base
Which element does the organic base of a nucleotide contain that isn’t in any other part of it?
Nitrogen
Do nucleotides form polymers?
Yes - like DNA and RNA
Give examples of polymers formed by nucleotides
DNA and RNA
What is ATP known as?
The universal energy currency of the cell
What is known as the universal energy currency of the cell?
ATP
Which process is ATP used in?
All processes requiring energy in all reactions in all living organisms
What is used in all processes requiring energy in all reactions in all living organisms?
ATP
Is there a living organism that doesn’t use ATP as the main energy transport system in the cell and why?
No - a cell would quickly die without a constant supply
Give 4 examples of cellular activities which use ATP
Protein synthesis
Active transport
DNA replication
Cell division
What do the following processes all use?
Protein synthesis, Active transport, DNA replication, Cell division
ATP
How is energy released from ATP?
By hydrolysing the bond between the last two phosphate groups in the molecule
Which bond is hydrolysed in order to release energy from ATP?
The bond between the last two phosphate groups in the molecule
What does hydrolysing the bond between the last two phosphate groups in a molecule do?
Releases energy from ATP
Equation for hydrolysing ATP
ATP + H20 —> ADP + Pi + H+
<—
What’s the approximate energy released when bonds are broken in ATP?
-30.6 kjmol-1
What type of reaction is it when bonds are broken in ATP? Why?
Exergonic as energy is released
What IS the energy released when breaking bonds in ATP?
Energy available for processes
Which products do we receive from hydrolysing ATP?
Adenosine diphosphate (ADP)
Inorganic phosphate (Pi)
Inorganic phosphate formed from hydrolysing ATP symbol
Pi
Pi
Inorganic phosphate formed from hydrolysing ATP
When does ADP form?
From hydrolysing ATP
Describe the ATP cycle
—> ATP —> energy for cellular work —> ADP + P —> Energy from respiration —>…
Phosphorylation
Adding a phosphate group
Adding a phosphate group
Phosphorylation
Which process is ATP made through?
Phosphorylation
Energy from metabolism to make ATP in humans
Break down of glucose using respiration
Energy from metabolism to make ATP in plants
Photons of light exciting electrons during photosynthesis
What does respiration and photosynthesis do?
Gives energy to form ATP
How much ATP do we use per day?
40kg
How much ATP is there at one point within our cells?
5g
Do we store ATP?
Nope
Why is there no need for us to store ATP?
It’s cycled, so the ATP is constantly remade and reused
Due to the process of making and using ATP being cycles, what is there no need for us to do?
Store it
Advantages of ATP
-Hydrolysis of ATP to ADP involved a single reaction that releases immediate energy
-Soluble and easily transported
-Only one enzyme (ATPase) is needed to release energy from ATP
-ATP releases energy in small amounts when and where needed
-ATP provides a common source of energy for many different chemical reactions (increases efficiency and control by the cell, the universal intermediary molecule between energy-yielding and energy-requiring reactions in the cell)
Example of ATP being soluble and easily transported
From companion cell to sieve element in Phoelem
Wha’t’s the only enzyme needed to release energy from ATP?
ATPase
How is ATP better than glucose in terms of the amount of reactions required to release energy?
ATP = a single reaction that releases immediate energy
Glucose = breakdown involves a number of intermediates and it takes much longer for energy to be released
How is ATP better than glucose in terms of the amount of energy released?
ATP = releases energy in small amounts when and where needed
Glucose = contains large amount of energy that may not be needed immediately
How is ATP better than glucose in terms of the enzymes needed to release energy?
ATP = only one enzyme needed to release energy (ATPase)
Glucose = requires many enzymes
What does DNA stand for?
Deoxyribonucleic acid
Made is the structure of DNA made up of?
Nulceotides, each including a Pentose deoxyribose sugar
What type of sugar do the nucleotides in DNA include?
Pentose deoxyribose sugar
What forms the backbone of DNA strands?
Nucleotides hooked together to make a sugar-phosphate backbone for each DNA strand
What do nucleotide units form in DNA?
Polymers known as the sugar-phosphate backbone
What happens for complementary base pairing in the DNA?
Adenine to Thymine
Cytosine to Guanine
What do Adenine, Thymine, Cytosine and Guanine all include?
Nitrogen
What is nitrogen included in all of?
The bases in DNA
What do the sequences of bases form in the DNA?
The genetic code
What forms the genetic code in the DNA?
The sequences of bases
Which type of bond is between Adenine and Thymine and how many?
2 hydrogen bonds
Which type of bond is between Cytosine and Guanine and how many?
3 hydrogen bonds
What two bases in the DNA have 1 hydrogen bonds between them?
Adenine and Thymine
Which two bases in the DNA have 3 hydrogen bonds between them?
Cytosine and guanine
Draw the structure of DNA
(Check notes)
What are different monomer units in the DNA joined by? What does this do?
A bond between the sugar and the phosphate of the next nucleotide, which forms the DNA molecule’s backbone
What maintains the DNA’s double helix shape?
Weak hydrogen bonds
What do weak hydrogen bonds maintain?
The double helix shape of the DNA
What are two strands of DNA linked together by?
Weak hydrogen bonds
How is the double helix shape of the DNA formed?
2 strands of DNA are linked together by weak hydrogen bonds and stacked like a ladder who’s sides spiral around each other into their double helix shape
Describe the polynucleotide chains/strands in DNA
Are anti-parallel to each other (running in opposite directions - 1 chain facing up, 1 chain facing down)
What are anti-parallel to each other in the DNA?
Polynucleotide chains/strands
How many nucleotide units does each polynucleotide chain in the DNA chain contain?
Many million (in pairs)
What do you call the chains of nucleotides joined together in the DNA?
Polynucleotide chains/strands
What can contain many million nucleotide units in pairs?
Each polynucleotide chain/strand
Name 4 scientists responsible for helping solve the structure of DNA
Erwin Chargaff
Rosalind Franklin
Watson & Crick
What were Erwin Chargaff, Rosalind Franklin and Watson & Crick all responsible for?
Helping solve the structure of DNA
What did Erwin Chargaff uncover?
% of Adenine = % of Thymine
% of Guanine = % of Cytosine
(Chargaff’s rule)
What is Chargaff’s rule?
% of Adenine = % of Thymine
% of Guanine = % of Cytosine
What did Rosalind Franklin do?
Shot X-ray beams at DNA samples and hypothesised a spiral structure
Who shot x-ray beams at DNA samples and hypothesised a spiral structure?
Rosalind Franklin
What do scientists do to uncover big things?
Use each other’s work
What did Watson and Crick do?
Used franklin’s x-ray pictures to build a model of DNA
Who used Franklin’s x-ray pictures to build a model of DNA?
Watson & Crick
What two things does Chargaff’s rule state?
% of Adenine = % of Thymine
% of Guanine = % of Cytosine
And
Ratio of purine to pyrimidine bases in DNA must always be 1:1
Describe purine bases
Double ring structure
Which bases have a double ring structure?
Purine bases
Describe pyramidine bases
Single ring stucture
Which bases have a single ring structure?
Pyrimidines
What connects adenine and thymine/ guanine and cytosine?
Hydrogen bonds
Name the purine bases
Adenine and guanine
Name the pyrimidine bases
Thymine and cytosine
What type of bases are adenine and guanine?
Purine
What type of bases are thymine and cytosine?
Pyrimidines
How do we remember which bases are Pyrimidines?
Thymine and cytosine have a “y” in them, like the word “pyrimidine”
What does adenine form a bond with?
Thymine OR uracil
What does uracil form bonds with?
Adenine
How many bonds are between adenine and thymine/uracil?
2 hydrogen bonds
How many bonds are between cytosine and guanine?
3 hydrogen bonds
Which bases form two hydrogen bonds?
Adenine with thymine/uracil
Which bases form 3 hydrogen bonds?
Cytosine with guanine
What does RNA stand for?
Ribonucleic acid
What is RNA?
A single stranded polynucleotide
Which type of nucleic acid is a single stranded polynucleotide?
RNA
Which Pentose sugar does RNA contain?
Ribose
Which nucleic acid containers the Pentose sugar ribose?
ATP and RNA
What type of bases are adenine, guanine, cytosine, thymine and uracil?
Organic bases
Which organic bases does RNA include?
Adenine, guanine, cytosine and uracil (no thymine)
Draw the difference between DNA and RNA
(Check notes)
What do the nucleotide units form in RNA?
A polymer
What forms a polymer in RNA?
Nucleotide units
Which is shortest - DNA or RNA?
RNA is much shorter than DNA
What are the three types of RNA?
mRNA - messenger
tRNA - transfer
rRNA - ribosomal
Compare DNA and RNA
(DNA first in the list each time, then RNA)
Deoxibose sugar v.s ribose sugar
Thymine v.s uracil
Double helix v.s single stranded
One type v.s 3 types (mRNA, tRNA and rRNA)
In the nucleus, mitochondria and chloroplasts v.s in the nucleus, cytoplasm and ribosomes
What’s the difference between the structure of DNA and RNA?
DNA lacks the OH- group at carbon no.2
Where is DNA found?
In the nucleus, mitochondria and chloroplasts
Where is RNA found?
In the nucleus, cytoplasm and ribosomes
What are both DNA and RNA?
Polynucleotide chains
What do mRNA, tRNA and mRNA all play a role in?
Protein synthesis
What is DNA’s role?
-Carries the code for protein synthesis
-structure of the protein is down to the DNA deciding the order the amino acids are in the polypeptide chain to form a code
How is the structure of a protein decided?
The DNA decided the order the amino acids are in the polypeptide chain to form a code
What must happen before cell division?
All of the DNA in the cell must be copied so that there’s a copy of each gene for both new cells (DNA replication)
DNA replication
Copying all of the DNA in a cell so that there’s a copy of each gene in both new cells after division
What’s the name for all of the DNA in a cell being copied so that there’s a copy of each gene in each new cell?
DNA replication
Why must DNA be copied in the cell before cell division?
So that there’s a copy of each gene for both new cells
How can we ensure that there’s a copy of each gene in both new cells following cell division?
DNA replication
The first step of cell division
The interphase - DNA is copied
What’s the interphase during cell division?
The first step, where DNA is copied
What’s the second step of cell division?
Mitosis, where the DNA is split equally into two daughter cells
Mitosis
Where DNA is split equally into 2 daughter cells
What’s the final step of cell division?
Cytokinesis, where the parent cell is cleaved in half
Cytokinesis
Where a parent cell is cleaved in half
What’s the name of the process where a parent cell is cleaved in half?
Cytokinesis
How is DNA stored in the cell?
Wrapped around histone protein molecules
Chromatin
Histone protein molecules packed together to form fibres, held in the nucleus
Histone protein molecules packed together to form fibres, held in the nucleus
Chromatin
How are chromosomes formed?
The thread-like structure of chromatin packs itself in tightly to form chromosomes when a cell starts to divide
What packs itself in tightly to form chromosomes?
Chromatin
What does chromatin packing itself in tightly form? When?
Chromosomes, when a cell starts to divide
Describe the structure of chromatin
Thread-like
Chromatid
A copy of the duplicated chromosome, which is generally joined to the other by a centromere
A copy of the duplicated chromosome, which is generally joined to the other by a centromere
Chromatid
What are chromatids joined together by and what does this form?
A centromere
A chromosome
Draw and label a chromosome
(Check notes)
What’s the reason for condensing DNA into chromosomes?
Prevents DNA tangling and damage during cell division
How is DNA tangling and damage prevented during cell division?
DNA is condensed into chromosomes
What’s the name of the process DNA uses for its replication?
Semi-conservative replication
Semi-conservative replication
The process DNA uses for its replication
Why is it called “semi-conservative replication”?
Half of the old molecule is kept
Describe semi-conservative replication in simple terms
1.Old molecule
2.Two polynucleotide strands unzip (hydrogen bonds break 1 by 1 down the strand) and new bases are added
3.Two new molecules are created, each containing 1/2 the original molecule
Describe the polynucleotide strands during DNA replication
Complementary
How do polynucleotide chains unzip during DNA replication?
Unzip, as hydrogen bonds break 1 by 1 down the strand
What do the hydrogen bonds breaking 1 by 1 occur during semi-conservative replication?
The polynucleotide chain to unzip
How many new molecules are created via semi-conservative replication?
2
What’s the name of the time where DNA replication happens before mitosis or meiosis?
Interphase
Interphase
The space of time when DNA replication occurs, before mitosis or meiosis
Where is 5’ labelled on the DNA structure?
Outside of the sugar’s structure
Where is 1’ labelled on a DNA’s structure?
First one clockwise from the oxygen (closest to the base)
Describe the strands of DNA
Anti-parallel - they run parallel to each other but in opposite directions
In which direction is DNA always synthesised?
5’-to3’ direction
What’s the 5’-to-3’ direction always required for?
Protein synthesis
Which end of the polynucleotide chain are nucleotides only ever added to?
The 3’ end of the growing strand
What binds to what in order to grow a polynucleotide strand?
5’ phosphate group of the new nucleotide binds to the 3’ OH group of the last nucleotide in the growing strand
What binds to the OH group on the last nucleotide in a polynucleotide chain and where?
5’ phosphate group at the 3’ OH group
What does the 5’ phosphate group bind to, where and to do what?
The 3’ OH group of the last nucleotide in the growing strand to form a polynucleotide
What’s the name of the original molecule that’s split into 2 other strands during DNA replication?
Parental DNA
Which two strands does the parental molecule split into during DNA replication?
Leading strand
Lagging strand
What’s the name of the shape formed during DNA replication?
Replication fork
Parental DNA
Original molecule for DNA replication
Replication fork
The shape produced during DNA replication
When does DNA replication occur?
During interphase - a phase in cell cycle between divisions
Interphase
A phase in cell cycle between divisions
What does helicase do?
Causes the parental DNA to unzip by breaking hydrogen bonds that expose the bases
Which enzyme is responsible for unzipping the parental DNA by breaking its hydrogen bonds?
Helicase
What type of bonds does helicase break when unzipping the parental DNA?
Hydrogen bonds
Where does helicase work?
In the replication fork
What does polymerase do?
Joins new, free nucleotides to their complementary bases to build a new DNA strand, by catalysing the formation of phosphodiester bonds between deoxyribose and phosphate groups
Which enzyme joins new, free nucleotides to their complementary bases?
Polymerase
How does polymerase join new, free nucleotides to their complementary bases?
Catalyses the formation of phosphodiester bonds between deoxyribose and phosphate groups
Phosphodiester bonds
Form between deoxyribose and phosphate groups (when polymerase joins free nucleotides to their complementary bases)
What type of bond forms between deoxyribose and phosphate groups (when joining complementary bases during DNA replication)?
Phosphodiester bonds
How does polymerase make near no mistakes?
Proof reading abilities
Which enzyme has proof-reading abilities and what does this help with?
Polymerase, which helps to make near no mistake when joining new, free nucleotides to their complementary bases
In which direction to polymerase enzymes build the new DNA strand?
5’ to 3’ direction
In which direction does polymerase move along the OLD DNA template?
In the 3’ to 5’ direction
Which template is moved along in the 3’ to 5’ direction during DNA replication by polymerase and why?
The old DNA template, as they build the NEW strand in the 5’ to 3’ direction
What do the original polynucleotide chains act as during DNA replication?
The template for the aligning of new nucleotides
What acts as the template for the aligning of new nucleotides during DNA replication?
The original polynucleotide chains
What’s the ONLY direction polymerase can work in, so what does it continue to do therefore?
5’ to 3’, so it keeps adding new bases to the 3’ end on the new strand
Which end on the new strand does polymerase keep adding bases?
3’
Which strand is worked on continuously by polymerase?
The leading strand
How is the leading strand worked on by polymerase?
Continuously
Why is the “lagging strand” called this?
It runs anti-parallel to the other strand, so polymerase has to keep moving back to add bases to the 3’ end
In which strand does polymerase have to keep moving back to add bases and where is it adding these bases?
“Lagging” strand, to the 3’ end
What does the fact that polymerase has to keep moving back to add bases to the 3’ end of the “lagging” strand do?
Creates disjoined fragments known as Okazaki fragments
Okazaki fragments
Disjoined fragments on the lagging strand
Why are Okazaki fragments present on the lagging strand?
As the strand runs anti-parallel to the other one, so the polymerase enzyme has to keep running back to add bases to the 3’ end
What does ligase do?
Glues the Okazaki fragments together, ensuring there’s no gaps in the DNA chain
Which enzyme glues Okazaki fragments together and what does this do?
Ligase, ensuring there’s no gaps in the DNA molecule
Which fragments does the ligase enzyme glue together during DNA replication?
Okazaki fragments
What happens when helicase has caused the entire DNA molecule to unravel?
Reactions occur to form covalent bonds between nucleotides
What’s the final step of DNA replication and when does this happen?
Reactions occur to form covalent bonds between nucleotides after helicase has completely unravelled the DNA molecule
What is our product at the end of DNA replication?
2 identical DNA molecules, each one made up of one newly synthesised chain and one from the original molecule
What does each DNA molecule synthesised during DNA replication consist of?
One newly synthesised DNA chain, and one from the original molecule
What’s the name of the experiment that decided that DNA replication occurs through the semi-conservative model?
Meselson and Stahl experiment
What did the Meselson and Stahl experiment do?
Decided on the semi-conservative model of replication for DNA replication
What was described as the most “beautiful experiment in Biology”?
The Meselson and Stahl experiment
What was meselson and Stahl’s experiment described as?
The most beautiful experiment in Biology
What were the 3 possible mechanisms for DNA replication at the time of the Meselson and Stahl experiment?
- Conservative replication
- Semi-conservative replication
- Dispersive replication
Conservative replication
The DNA molecule would be copied from the original, leaving the original DNA molecule as it was and having a new copy
What’s the name of the type of DNA replication where the DNA molecule would be copied from the original, leaving the original DNA molecule as it was and having a new copy?
Conservative replication
Semi-conservative replication
The two polynucleotide chains would part, and new nucleotides attach to each of the chains, leading to each new molecule having both an original chain and a new one
What’s the name of the type of DNA replication where the two polynucleotide chains would part, and new nucleotides attach to each of the chains, leading to each new molecule having both an original chain and a new one ?
Semi-conservative replication
Dispersive replication
Sections of the DNA molecule would be copied and spliced together, making each new DNA molecule a mix of original and new DNA
What’s the name of the DNA replication model where sections of the DNA molecule would be copied and spliced together, making each new DNA molecule a mix of original and new DNA?
Dispersive replication
What was used as the DNA source in the Meselson and Stahl experiment?
E.coli bacteria
What was E.coli bacteria used for in the Meselson and Stahl experiment?
The source of DNA
Why was E.coli bacteria used as the source of DNA in the Meselson and Stahl experiment?
-easily grown in a flask of culture medium
-replicate their cells (and DNA) every 20 minutes under optimal conditions
How often do E.coli bacteria replicate their cells (and DNA) and under which conditions?
Every 20 minutes under optimal conditions
What do E.Coli bacteria cell do every 20 minutes under optimal conditions?
Replicate their cells (and DNA)
How were ‘new’ and ‘old’ nucleotides distinguished in the Meselson and Stahl experiment?
By the isotope of Nitrogen in the nitrogenous bases
What did the isotope of nitrogen in the nitrogenous bases help do in the Meselson and Stahl experiment?
Distinguish ‘new’ and ‘old’ nucleotides
What were the 2 isotopes of nitrogen used in the Meselson and Stahl experiment?
15N and 14N
What’s the normal nitrogen isotope of E.coli bacteria?
14N
Which part of the nucleotide contained the nitrogen isotopes in the Meselson and Stahl experiment?
The nitrogenous bases
Which nitrogen isotope was heaviest in the Meselson and Stahl experiment?
15N (heavier than 14N)
How can the different isotopes of nitrogen be separated in the Meselson and Stahl experiment?
Separated by mass via centrifugation
Why does centrifugation work to separate the nitrogen isotopes in the Meselson and Stahl experiment?
They have different masses, and centrifugation separates by mass
What’s the first stage of the Meselson and Stahl experiment?
DNA was extracted from E.Coli in a growth medium containing the 14N isotope and put in the centrifuge
How does a centrifuge work for the Meselson and Stahl experiment?
Turns the sample at high speeds which settles the DNA
It settles at about the same level due to it having the same density
Forms a band in the tube
How does a DNA band form in the tubes from a centrifuge?
DNA settles at about the same level due to it having he same density
What’s the name of the device used to turn the DNA samples at high speeds to form bands in the tube in the Meselson and Stahl experiment?
Centrifuge
What does a centrifuge separate by?
Mass
What would appear in the tube after centrifugation for the E.coli in a growing medium containing the 14N isotope?
A singular band in the light position
What’s the second step of the Meselson and Stahl experiment?
Extract E.coli DNA from a sample in a growing medium containing the 15N isotope that’s been allowed to replicate over many generations and place this into a centrifuge
What would appear in the tube after centrifugation of an E.coli sample that’s been in a growing medium containing the 15N isotope?
The band of DNA settles lower down in the tube than the DNA from the 14N growing medium
Why does the DNA band lie lower down in the tube for the 15N growing medium compared to the 14N growing medium?
15N is heavier/more dense
What does the fact that the 15N isotope is heavier than the 14N isotope cause in the Meselson and Stahl experiment?
The band of DNA from the sample in this growing medium settles lower down in the tube
How do all of the bases in the extracted DNA sample form the 15N sample all contain 15N?
They’ve been allowed to replicate over many generations
What does allowing E.coli to replicate over many generations in the 15N growing medium cause?
All of the nitrogenous bases to contain 15N
What’s the third step of the Meselson and Stahl experiment?
The sample from the 15N growing medium is washed and placed back in the 14N medium to replicate for 1 generation before extracting the DNA and centrifuging it
What must be done before placing the DNA sample from the 15N into the 14N growing medium?
It must be washed
How many generations is the E.coli allowed to replicate for in the 14N medium following previously being in the 15N medium?
1 generation
What was shown on the tube when the DNA sample was centrifuged following the E.coli being in both the 15N growing medium and the 14N growing medium for 1 generation?
DNA was found at the intermediate position between the 14N and 15N bands
What’s the name of the position the DNA band lies between the 14N and 15N bands?
Intermediate position
What do we label the DNA bands on the test tubes in the Meselson and Stahl experiment?
Light
Intermediate
Heavy
What did the DNA sample found at intermediate between the 14N and 15N bands prove?
That replication is not conservative, as each new DNA molecule consists of half new 14N nucleotides and half 15N nucleotides, whereas the conservative model would show 2 separate bands
What would the conservative model of DNA replication have shown as the DNA bands in the Meselson and Stahl experiment? How was this proved wrong?
2 seperate bands, however we received a band in intermediate position between 14N and 15N, showing that each DNA molecule consists of half new 14N nucleotides and half 15N nucleotides
What did the line in the intermediate position between the light and heavy positions of DNA not rule out?
The dispersive model
How was the dispersive model ruled out in the Meselson and Stahl experiment?
E.coli as allowed to replicate 2 more times in the same external medium, leading to generations 2 and 3
How many times was the E.coli allowed to replicate and in which external medium for the final stage of the Meselson and Stahl experiment?
Twice in the same 14N external medium
What did generation 2 when E.coli was left in the same 14N external medium reveal in the tube?
The bands appeared at the light and intermediate positions, showing that the replication was not dispersive
How was it proved that DNA replication was not dispersive in the Meselson and Stahl experiment?
When left in the 14N growing medium to generation 2, the bands appeared at the light and intermediate positions
What would the dispersive model have shown when E.coli was left to replicate in the 14N growing medium to generation 2 in the Meselson and Stahl experiment?
All the DNA molecules in generation 2 would have more 14N than N and the DNA would appear between the intermediate and light position
What did the tube from generation 2 in the 14N growing medium prove in the Meselson and Stahl experiment?
The parental DNA molecules of one light and one heavy chain had parted and each had been used as a template for the new nucleotides to attach to
What did the ‘heavy’ chain cause in the final DNA replication of the E.Coli in the 14N external medium?
The DNA molecule in the intermediate position, but getting thinner over the next generations
What did the ‘light’ chain show in the final DNA replication stage in the 14N external medium of the E.coli?
New nucleotides attached from the light 14N medium, so the band in the light position got thicker
How did the DNA band in the light position get thicker in the final E.coli DNA replication stage?
New nucleotides attached from the light external medium - there was more light DNA developing per generation
Which DNA replication model was the only one left supported by the Meselson and Stahl experiment?
The semi-conservative replication model
Where is the genetic code?
On the DNA
What does the genetic code do?
Instruct the cell on which order to put the amino acids in a polypeptide chain
What instruct the cell on which order to put the amino acids in a polypeptide chain?
Genetic code
What’s the sequence of amino acids in a polypeptide chain responsible for?
The primary structure of a protein and how it works
What is responsible for the primary structure of protein and how it works?
The sequence of amino acids in the genetic code
Gene
Length of DNA that codes for a specific polypeptide
Length of DNA that codes for a single polypeptide
Gene
What does an intron code for?
Nothing
Which part of a gene codes for nothing?
Introns
What do exon’s do in a gene?
Code for part of the polypeptide
What are repsonsible for coding for part of the polypeptide in a gene?
Exons
What contains 100s and 1000s of genes coding for different polypeptides?
Chromosomes
What do chromosomes contain?
100s and 1000s of genes coding for different polypeptides
What carries the genetic information to build the primary structure of a single polypeptide?
The sequences of bases which make up a gene
What do the sequences of bases which make up a gene do?
Carry the genetic information to build the primary structure of a single polypeptide
What make up a gene?
Sequences of bases
What do 3 bases code for?
1 amino acid
What codes for 1 amino acid?
3 bases
What are the three bases that code for 1 amino acid known as?
The triplet code/codon
Codon
Three bases that code for 1 amino acid
What does protein synthesis require (in short)?
-the transcription of a gene into a mRNA molecule, from the original DNA template
-the code within the mRNA molecule is translated into a polypeptide by a ribosome
Which process requires the transcription of a gene into a mRNA molecule, from the original DNA template and the code within the mRNA molecule is being translated into a polypeptide by a ribosome?
Protein synthesis
Write the steps of transcription
(Check notes)
What causes DNA to unwind and unzip at a particular region to be copied?
Helicase enzyme
What does helicase do?
Unwinds and unzips a particular region of the DNA to be copied
How DOES helicase unzip DNA?
Breaks hydrogen bonds between complimentary bases
How many coding strands are used in transcription and what happens to it?
Only 1, the enzyme polymerase attaches to the DNA at the beginning of the sequence to be copied
What does the enzyme polymerase do to the DNA?
Attaches itself at the beginning of the sequence to be copied
How does transcription itself actually occur?
Free RNA nucleotides align themselves opposite complimentary nucleotides on the coding DNA strand
What align themselves opposite complimentary nucleotides on the coding DNA strand during transcription?
Free DNA nucleotides
What do free RNA nucleotides do during transcription?
Align themselves opposite complimentary nucleotides on the coding DNA strand
Which strand of DNA does RNA polymerase move along?
The coding strand (the bottoms strand)
What does RNA polymerase do as it moves along the coding DNA strand?
Forms bonds that add nucleotides one at a time to the RNA (pre mRNA)
What forms bonds that add nucleotides one at a time to RNA during transcription?
RNA polymerase moving along the coding DNA strand
What’s left when nucleotides have all been added to the coding DNA strand by the RNA polymerase?
A molecule of mRNA alongside the unzipped portion of DNA
What happens behind RNA polymerase during transcription?
DNA strands re-join to form their double helix
Where does DNA rejoin to form a double helix during transcription?
Behind the RNA polymerase
What’s the final step of transcription?
mRNA carries the DNA code out of the nucleus through a nuclear pore to the cytoplasm and attaches itself to a ribosome
How does mRNA exit the nucleus?
Through the nuclear pore
Where does mRNA carry the DNA code following transcription?
Out of the nucleus and into the cytoplasm to attach itself to a ribosome
Where does transcription happen?
All in the nucleus
Does the DNA ever leave the nucleus?
No
What does DNA act as in transcription?
A template for the production of mRNA (messenger RNA)
What’s the name for an mRNA molecule receiving the DNA’s genetic code?
Transcription
What’s the name for an mRNA molecule being transferred into a polypeptide by a ribosome?
Translation
How do we modify pre-mRNA before moving onto the translation stage of protein synthesis?
Edit out the introns
What’s edited by removing mitrons?
Pre-mRNA
What’s the name of the process of modifying pre-mRNA to mRNA before the translation stage of protein synthesis?
Post-transcriptional modification of pre mRNA to mRNA
What’s the first stage of post-transcriptional modification of pre-mRNA?
Introns are removed (spliced out) aided by enzymes containing RNA that hydrolyse the bonds between nucleotides
What’s the name for the removal of introns?
Splicing
Splicing
Removing introns of unknown function from pre-mRNA
How are introns spliced out from pre-mRNA?
By enzymes containing RNA, that hydrolyse the bonds between nucleotides
What are introns for?
We don’t know, but they’ve been in DNA for millions of years through evolution, so they must have some sort of purpose
What’s the final step of post-transcription modification of pre mRNA?
Exons are joined together to form mRNA
Steps of post-transcriptional modification of pre mRNA
- Introns are removed (spliced out) by enzymes containing RNA
- Exons are joined together to form mRNA
What happens in Eukaryotes during splicing?
Non-coding DNA/RNA of unknown function (introns) are removed, and exons which code for the protein are joined together
Where does splicing occur?
Is thought to occur in the nucleus of the cytoplasm
Does splicing occur in prokaryotes? Why?
No, as they have continuous genes that don’t contain introns
What type of cells contain introns and which don’t?
Eukaryotes do
Prokaryotes don’t
How is the base sequence on an mRNA molecule read by a ribosome?
In groups of 3 bases at a time, known as codons
How many codons are available for each amino acid?
More than one
What does each codon code for?
Only ONE specific amino acid
Describe genetic code across all species and describe what this means
Universal - each codon codes for the same amino acid in ALL species
What does the fact that each specific codon codes for the same amino acid in all species show?
That genetic code is universal
What are codons used to make?
A polypeptide chain
What are the mRNA codons for the following DNA template?
TAC
AUG
(Remember - in RNA, the complementary base pair of adenine is uracil, not thymine)
Complementary base pair of adenine in RNA
Uracil
What is uracil’s complementary base pair?
Adenine
What is AUG?
The initiation codon
Initiation codon code
AUG
What is added with the initiation codon, AUG?
The amino acid methionine
When is the amino acid methionine added to a polypeptide chain?
With the AUG initiation codon
What does the AUG initiation codon do?
Tells the ribosome when to start making the polypeptide
What tells the ribosome when to start making the polypeptide?
The initiation codon, AUG
What happens to the AUG initiation codon if it has no role and when?
Can be removed during post-transactional modification in the Golgi body
What could be removed during post-translational modification in the Golgi body and when?
The initiation codon (AUG) if it has no role
Stop codons
UAA, UAG, UGA
What are UAA, UAG, UGA all examples of?
Stop codons
What do stop codons do?
Tell the ribosome when to stop making a polypeptide
What tells a ribosome when to stop making a polypeptide?
A stop codon (UAA, UAG or UGA)
Why is the code a triplet code?
Three bases in the code give enough combinations to code for all 20 amino acids, as we need at least 1 unique combination for each
How many amino acids do we have and what do we require for each?
20, we need at least 1 unique base combination for each one
How many different codes would 2 bases in a codon give us?
4^2 - 16 different codes (not enough)
How many different codes does having 3 bases in a codon give us?
4^3 - 64 codes
What’s the word to describe the fact that we have more than 1 codon per amino acid?
Our genetic code is degenerate
What is “degenerate” for us and why?
Our genetic code, as we have more than 1 codon per amino acid
Why is the fact that our genetic code is degenerate advantageous to our cells?
If there were to be a mutation in the codon, the mutation may change the codon to another codon which codes for the same amino acid, which prevents against the mutation affecting the functionality of the protein
What prevents mutation affecting the functionality of our proteins?
The fact that our genetic code is degenerate
What is prevented through a degenerate genetic code?
The affects of mutation
What has to happen for the translation stage of protein synthesis to occur?
Transfer RNA (tRNA) has to be binded to an amino acid
What does tRNA have to be binded to for translation to occur?
An amino acid and to mRNA
Draw tRNA
(Check notes)
How is the type of amino acid attached to tRNA determined?
The anticodon sequence of the tRNA
What does the anticodon sequence of the tRNA determine?
The type of amino acid attached to the tRNA
How many amino acids does each tRNA molecule bind to?
1 specific amino acid
What is tRNA responsible for?
Transporting amino acid from the cytoplasm to the ribosome in order to create a polypeptide
What’s responsible or transporting amino acids from the cytoplasm to the ribosome to form a polypeptide?
TRNA
Where does tRNA transport amino acids to and from and for what?
From the cytoplasm to the ribosome to create a polypeptide
What is transported from the cytoplasm to the ribosome to form a polypeptide by tRNA?
Amino acids
What has to happen in order for tRNA to be re-used
It needs to be re-activated
When does tRNA need to be reactivated?
When tRNA has left the ribosome and amino acid
What has to be re-activated upon leaving the ribosome and amino acid?
TRNA
What are the steps in tRNA activation?
-tRNA activating enzyme
-enzyme binds to ATP which provides energy and a specific amino acid
-amino acid-AMP complex is formed and a specific tRNA molecule is recruited
-the tRNA is bound to the amino acid and AMP is released
-“charged” tRNA is produced
What does tRNA have to be in order to be re-used?
Charged
Draw and label a ribosome during translation
(Check notes)
How many attachment sites does each ribosome have for translation and what are they?
2 - P site and A site
Which organelle has the P site and A sit for the translation stage of protein synthesis?
Ribosome
How many tRNA molecules can occupy 2 sites on a ribosome at any given time?
2
How is the mRNA code read by the ribosome?
In groups of 3
What does the ribosome read in groups of 3?
The mRNA code
Where does the ribosome detach from the mRNA molecule?
When it reaches a stop codon
What happens when a ribosome reaches a stop codon?
Detaches from the mRNA molecule
What must be complementary during translation?
The anticodon sequence of the tRNA’s to the codon on the attached mRNA molecule
How does tRNA enter the attachment site of a ribosome during translation?
The anticodon sequence of the tRNA must be complementary to the codon n the attached mRNA molecule
What happens when the anticodon sequence of tRNA is complementary to the codon on the attached mRNA molecule?
A codon-anticodon complex forms with hydrogen bonds forming between complementary bases of the codons
How is a codon-anticodon complex formed?
With hydrogen bonds between complimentary bases of the codons
What have HYDROGEN bonds during the translation stage of protein synthesis?
The complimentary bases of the codons
What has a PEPTIDE bond during the translation stage of protein synthesis?
Between 2 amino acids carried by tRNA
What occurs between 2 amino acids carried by tRNA during the translation stage of protein synthesis?
Peptide bonds
What happens during the translation stage of protein synthesis once a peptide bod is formed between 2 amino acids carried by tRNA?
The ribosome moves along the mRNA to the next codon
What happens when the ribosome moves along the mRNA to the next codon during translation?
The first tRNA leaves without its amino acid
How does the tRNA molecule leave the attachment site of the ribosome during translation?
Without its amino acid
When does tRNA leave the attachment site of a ribosome without its amino acid?
When the ribosome moves along to the next codon
What happens when the first tRNA leaves the attachment site of a ribosome during translation?
A new tRNA with an anticodon complementary to the new codon in the second attachment moves in
Which sites does tRNA move to and from and repeats this?
From the A site to the P site
What happens as the process of translation continues?
A polypeptide molecule is built up, 1 amino acid at a time
How is a polypeptide molecule built up?
1 amino acid at a time through translation
What happens when the ribosome reaches a “stop” codon on the mRNA molecule during translation?
The ribosome dissociates and a newly formed polypeptide chain is released, which is the primary structure of protein
When does a ribosome dissociates form an mRNA molecule and a newly formed polypeptide chain is released, which is the primary structure of protein?
Upon reaching the “stop” codon
What IS the polypeptide chai released at the end of translation?
The primary structure of protein
Where does the primary structure of protein move following translation? Why?
To the Golgi body for modification (e.g - folded to form the secondary protein structure)
What is translated into what during the translation stage of protein synthesis?
The sequence of codons on the mRNA
To
The primary structure of a new proton molecule
What does this entire unit come back to?
Francis Crick’s Central Dogma (of molecular Biology)
What moves to the Golgi body?
The primary structure of protein
Francis Crick’s Central Dogma (of molecular Biology)
An explanation of the flow of genetic information within a biological system
What gives an explanation of the flow of genetic information within a biological system?
Francis Crick’s Central Dogma (of molecular Biology)
What is Francis Crick’s central Dogma (of molecular Biology) summed up as?
DNA makes RNA makes protein
Transcription summed up under Francis Crick’s Central Dogma (of molecular Biology)
The DNA is copied in the nucleus to form messenger RNA (mRNA)
Translation summed up in Francis Crick’s Central Dogma (of molecular Biology)
The mRNA associated with a ribosome and transfer RNA (tRNA) brings amino acids to form a polypeptide
What does Francis Crick’s Central Dogma (of molecular Biology) cover?
Transcription, translation and codons
Codes on an mRNA molecule summed up in Francis Crick’s Central Dogma (of molecular Biology)
The code is arranged in codons (triplet of bases) which are matched by complementary anti-codons on tRNA
2 processes of protein synthesis?
Transcription
Translation
What type of reaction is ATP formed in and why?
Endergonic as it uses energy
Endergonic - definition and example
Uses energy - forming ATP
Give an example of an exergonic reaction and explain what this is
Hydrolysis of ATP
A reaction that releases energy
What is the reaction condensing ADP and Pi to make ATP?
Reversible
Draw and label ADP
(Check notes)
Is uracil a purine or a pyrimidine?
A pyrimidine
What does Chargaff’s rule not apply to and why?
RNA as the proportions of bases are not equal due to the molecules being single stranded
What rule does not apply to RNA and why?
Chargaff’s rule, as the bases are not in equal proportions in RNA, as molecules are single stranded
What does having single stranded molecules in RNA mean?
Chargaff’s rule doesn’t apply
Why are the bases not in equal proportions in RNA?
As it’s single stranded
What’s the product of transcription?
RNA
Where does transcription occur?
Nucleus
What’s the product of translation?
Polypeptide amino acid chain
What’s the location of translation?
Cytoplasm and endoplasmic reticulum (ribosome)
Give 2 differences between translation and transcription
Transcription -
Product = RNA
Location = Nucleus
Translation -
Product - polypeptide amino acid chain
Location - cytoplasm and endoplasmic reticulum (ribosome)
Does transcription or translation occur in the nucleus?
Transcription
Does transcription or translation occur in the cytoplasm and endoplasmic reticulum (ribosome)?
Translation
What’s RNA the product of?
Transcription
What’s a polypeptide amino acid chain the product of?
Translation
Which variables should be controlled during the centrifugation in the Meselson and Stahl experiment?
-time
-rate of spin
-temperature
-volume of DNA sample
-concentration of tube contents
Which parts of the molecule are in common to DNA, RNA and ATP nucleotides?
Pentose sugar
Phosphate groups
Nitrogenous bases
What is meant by the term “universal energy currency’?
ATP is required in all energy requiring reactions in all living organisms
Is hydrolysing ATP to ADP exergonic or Endergonic and why?
Exergonic as approximately 30.6kJmol is released
How many nucleotides make up one amino acid?
3
Are tRNA specific?
Yes, to each amino acid
What’s specific to each amino acid?
tRNA
Which organelle contains DNA?
Nucleus
What part of a cell makes rRNA and assembles ribosomes?
Nucleolus
What does a nucleolus do?
Makes rRNA and assembles ribosomes
Name 3 ways in which the Golgi Body can process a polypeptide into a functional protein
-folding to give secondary/tertiary structure
-adding carbohydrate chains
-combining polypeptides
Which organelles produce ATP?
Mitochondria and chloroplasts
What do mitochondria and chloroplasts synthesise?
ATP
What’s the difference between where transcription and translation take place?
Transcription - nucleus
Translation - ribosome
Describe 3 differences between tRNA and mRNA
tRNA
Clover shape
Double stranded sections
Caries an amino acids to the growing polypeptide chain during translation
mRNA
Linear
Single stranded
Carries genetic information copied from DNA
How many nucleotides are there per amino acid?
3
How does a peptide bond form between 2 amino acid molecules?
Via a condensation reaction
How happens of introns are included in the amino acid sequence?
A different protein structure would be produced
What do exons code for?
The protein
How many nucleotides make up an amino acid and why?
3 nucleotides, as there is one base on each nucleotide and 3 bases make up one amino acid
What does DNA helicase do?
Breaks the hydrogen bonds between bases
Where would the band in the centrifuge tube remain throughout for dispersive replication?
Intermediate positions (except generation 1)
Which mechanism for DNA replication involves no intermediate DNA?
Conservative
What is more ATP in muscles advantageous for?
Contraction
What type of reaction is translation and why?
Endergonic
Uses ATP
How does the peptide bond form between 2 amino acid molecules during translation?
Part of the ribosome acts as a catalyst
Difference between DNA replication and transcription
DNA polymerase and DNA nucleotides
RNA polymerase and RNA nucleotides
What does a gene code for?
One polypeptide
Why can’t DNA be replicated outside of the nucleus of a cell?
Free DNA nucleotides are not outside of the nucleus
Which codons code for amino acids?
mRNA codons
Is DNA reactive? What does this allow us to do?
No, its very Unreactive
Bases in the core are protected by the sugar phosphate backbone
It means that it lasts millions of years under the right conditions
What do we measure the length of DNA in?
Base pairs
What does ligase do?
Joins fragments of DNA to an existing fragment
What’s the name for the method used in Meselson and stahl’s experiment?
Ultracentrifugation
What does DNA replication form?
The sugar phosphate backbone
Which carbon is the base attached to in DNA?
C1
Which carbon is the phosphate group attached to in DNA?
C
What do the bonds between nucleotides to form DNA strands attach between? In which direction?
Phosphate and C3, in the 5’ to 3’ direction
