🔻✅1.5 -The Structure Of Nucleic Acids And Their Functions Flashcards
What are nucleic acids?
Polymers made out of monomers called nucleotides
What is the name of a molecules containing many nucleotides?
Polynucleotide
How many nucleotides do polynucleotides contain?
Millions
What forms a nucleotide (3)
- Phosphate group
- pentode sugar
- organic base
Does the phosphate group have the same or different structure in all nucleotides
Same
Give an example of the pentode sugar in DNA/RNA
Deoxyribose in DNA
Ribose in RNA
Name another name for the organic base in a nucleotide
‘Nitrogenous base’
What 2 groups can the organic base be split into? Give examples
Pyrimidine (Thymine, Cytosine, Uracil)
Purine (adenine and guanine)
What must happen in a chemical process
Bonds must be made/broken for a chemical process to occur
What are heterotrophic organisms? How do they obtain chemical energy?
Animals, obtain chemical energy through food
What are autotrophic organisms? How do they obtain chemical energy
Green plants, obtain energy through light which is converted into chemical energy via photosynthesis
What is ATP
Adenosine triphosphate
Why is ATP a form of energy currency not storage?
Because it’s involved when energy changes occur, it is synthesised when energy is made available
Where is ATP broken down
Broken down in the mitochondrion when energy is needed
Name the component of ATP you would find in its chemical diagram
Adenine + Ribose + 3 phosphate groups
What is the enzymes that hydrolyses ATP
ATPase
What does ATPase do?
It hydrolyses the bond between the second and third phosphate groups in ATP, removing the third and creating ADP (adenosine diphosphate) with the release of energy
How much energy is release when 1 mole of ATP is hydrolysed
30.6 KJ (when the bond breaks)
Name the name of a reaction which releases energy
Exergonic reaction
Name the name of a reaction which requires energy input
Endergonic reaction
Name the ATP reversible reaction.
ATP + water —<> ADP + P1
^H = -30.6 KJ mol -1
What does the ^H = -30.6 KJ mol -1 indicate In the ATP equation?
Means that there is a negative heat change and therefore energy is released
Why can’t you put + energy at the end of the ATP equation
Because chemical energy is not a material
Name the process where phosphate is added to ADP to form ATP
Phosphorylation
What does ATP do in terms of energy transfer
Transfers free energy from energy rich compounds e.g glucose to cellular reaction where it is needed
Name the process where energy is realised gradually
Respiration
Name the 4 advantages of having ATP as an intermediate in providing energy compared with the direct use of glucose:
1) Hydrolysis of ATP to ADP releases energy immediately. Breakdown of glucose involves many intermediates and takes longer
2) Only 1 enzyme (ATPase) is needed to release energy from ATP, many are needed for glucose
3) ATP releases energy in small amounts when needed, glucose releases energy in large amounts at once
4) ATP is a common source of energy for many different chemical reactions increasing efficiency and control by the cell
Why is it inefficient to only derive chemical energy from the breakdown of glucose
Because too much energy would be lost at one time; therefore heat would increase and destroy cells
Name the 5 roles of ATP (cellular activity)
1) metabolic processes —> builds large complex molecules (DNA from nucleotides)
2) Active transport —> changes the shape of carrier proteins in membrane and allows molecules/ions to moved against a concentration gradient
3) movement —> muscle contraction
4) secretion —> packaging and transport of secretory products into vesicles
5) nerve transmission
What forms a double helix
2 polynucleotide strands wound around each other in a double helix
What is the pentose sugar in DNA nucleotides
Deoxyribose
How many organic bases are there in DNA
4
What are the purine bases in DNA
Adenine and guanine
What are the two pyrimidine bases in DNA
Cytosine and Thymine
What forms the backbone of the helix
The deoxyribose sugar and phosphate groups on the outside of the DNA molecule
What is the complimentary base to Adenine
Thymine
What is the complementary base to cytosine
Guanine
What maintains the shape of a double helix
The hydrogen bonds which join the bases to form complimentary base pairs
What is the shape of a DNA molecule
Long and thin, tightly coiled inside a choromosome
How Large is the diameter of the double helix
2nm
How long is DNA molecule number 1
85 nm
Describe the stands
Antiparallel (parallel but facing opposite directions)
How many hydrogen bonds are there between Adenine and Thymine?
2
How many hydrogen bonds are there between cytosine and Guanine?
3 hydrogen bonds
What does DNA carry?
Large value of genetic information
Why are the 2 polynucleotide strands able to separate?
Because they are held together by hydrogen bonds
How is genetic information protected inside DNA
The base pairs are on the inside of the double helix with deoxyribose phosphate backbones
Is DNA a stable or unstable molecule?
What does this allow
Stable
Allows information to pass unchanged from generation to generation
What pentose sugar does RNA contain?
Ribose
Is RNA a single or double stranded polynucleotide?
Single stranded
What purine bases does RNA contain?
Adenine and Guanine
What pyrimidine bases does RNA contain?
Cytosine and Uracil
Name the 3 types of RNA involved with protein synthesis
Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)
Describe mRNA
- long single stranded molecule
- synthesised in the nucleus
- Different mRNA have different lengths, related to the genes where they are synthesised
Where does mRNA carry genetic code?
Carries genetic code from the DNA to the ribosomes in the cytoplasm
Describe rRNA
Example of use
-found in cytoplasm
-comprises large complex molecules
E.g ribosomes are made from rRNA and protein
What happens in rRNA
Site of the translation of the genetic code into proteins.
Describe structure (basic) of transfer RNA
Small single stranded molecule
-folds so that in some places there are base sequences forming complimentary base pairs
What is the shape of transfer RNA described as?
Clover Leaf
What does the 3’ end of a tRNA molecule have the base sequence as?
What happens at this point?
What else would this tRNA carry?
Cytosine, cytosine, adenine
- location where Specific amino acid that the molecule carries attaches
- also carries a sequence of 3 bases called the anticodon
What does transfer RNA do?
Molecules of tRNA transport specific amino acids to the ribosomes in protein synthesis
Name the pentose sugars in DNA vs RNA
Deoxyribose vs ribose
Name the purine bases in DNA vs RNA
Guanine and Adenine in both
Name the pyrimidine bases in DNA vs RNA
Cytosine and Thymine vs Cytosine and Uracil
How many strands in DNA vs RNA?
2 in DNA (Double helix)
1 in RNA (single strand)
Compare the lengths of DNA vs RNA
Long (DNA) vs Short
tRNA and rRNA = short, mRNA varies but is always shorter than DNA
Who proposed the molecular theory of DNA?
When?
Helped by who?
Watson and Crick
1953
Helped by Franklin and Wilkins
Where is DNA in in Eukaryotic cells?
Enclosed in the nuclei
Small molecules in chloroplasts and mitochondria
Where is DNA in prokaryotic cells
Loose in the cytoplasm
Some viruses
Name the two main roles of DNA:
1) Replication
2) Protein synthesis
What is replication
If two strands of a double helix are separated, two identical double helices can be formed, as each parent strand can act as a template for the synthesis of a new complementary strand
Define protein synthesis
The sequence of bases represents the information carried in DNA and determines the sequence of amino acids in proteins
What is the term given to the copying of DNA
Where does this occur
Replication.
In the nucleus during interphase
Name the 3 possibilities initially derived for the mechanism of DNA
- conservative replication
- semi-conservative replication
- Dispersive replication
Describe conservative replication
Where the parental double helix remains intact (conserved) and a whole new helix is made
Describe semi-conservative replication
Mode of DNA replication in which each strand of a parallel double helix acts as a template for the formation of a new molecule, each containing an original, parental strand and a newly synthesised, complimentary daughter strand
What is dispersive replication?
Idea that two new double helix’s contain fragments from both strands of the parental double helix
What is the correct form of replication proposed by Watson and Crick
The semi-conservative replication
What was Meselson-Stahl experiment focussed on?
Provided conclusive evidence of the semi conservative hypothesis through his study of Nitrogen
What did Meselsohn and Stahl culture?
Cultured the bacterium ‘Escherichia Coli’ for several generations in a medium containing amino acids made with the heavy isotope 15Nitrogen opposed to lighter isotope 14Nitrogen
What happened to the bacteria where cultured in the 15Nitrogen?
It incorporated the 15Nitrogen into their nucleotides and then DNA so the DNA eventually only contained 15Nitrogen
What did Meselsohn and Stahl do after extracting the bacterial DNA?
What did they find?
Centrifuged it and found the DNA settled at a low point in the tube because 15N made it heavy
After the centrifuge, the N15 was washed, why is this important?
Important as it stops contaminating 14N with the 15N do that 15N was not in any new DNA strands
After adding the 15N bacteria to a medium containing lighter isotope 14N and allowing it to divide what do you do?
What was the findings?
DNA from the first generation culture was centrifuged and had a mid point density
What did the first generation culture having a mid point density show?
Rules out conservative replication because that would produce a band showing the parental molecule that was entirely heavy
Where did DNA from the second generation settle in the tube?
Discuss their densities
Settled at the mid point and the high point in equal amounts, midpoint had intermediate density and high point contained 14N only
What did the results from the second generation show?
Ruled out dispersive replication because, if that were the case there would always be a mixture of light and heavy in every strand, and only 1 band would form.
Why is the Meselsohn-Stahl experiment conclusive evidence of semi-conservative hypothesis?
Because one parental trans is conserved
Describe the stages first stage in semi-conservative replication.
- The hydrogen bonds holding the base pairs together break in the double helix
- The DNA unwinds, catalysed by the enzyme helicase and the two strands of the molecule separate
What happens in the second stage of semi-conservative replication
The enzyme DNA polymerase catalysed the condensation reaction between the 5’ -phosphate group is a free nucleotide to the 3’ OH in the growing DNA chain
- each chain acts as a template and free nucleotides are joined to their complementary bases
- newly synthesised daughter strands form
What is DNA
DNA is a store of genetic Information, coded in the sequence of bases in the DNA in thousands of sections along its length called genes
Describe how DNA determine the characteristics of an organism
DNA base sequence directs which amino acids join together :: which proteins/enzymes are made :: which reactions take place in an organism
What is the triplet code
The idea that 3 based code for 1 amino acid
What evidence supports the theory of the triplet code
4 bases of DNA (thymine, guanine, Cytosine and Adenine)
- if 1 bade coded for 1 amino acid there would be 4 combinations
- if 2 bases coded for an amino acid there would only be 16 combinations
- proteins are made of 20 different amino acids :: 3 bases coding for 1 amino acid produces 64 possibilities :: suitable
How many possible triplet code combinations are there?
How many amino acids are required for a protein to form?
- 64 amino acid combinations
- 20 amino acids in each protein
Why is the genetic code described as ‘degenerate’ or ‘redundant’?
Because one triplet can encode each amino acid
What does the phrase “the genetic code is punctuated” mean?
It means there are 3 triplet codes that do not code for amino acids. In mRNA they are called ‘stop’ codons and mark the nare d if the portion to be translated
Summarise the 5 characteristics of the genetic code
- Triplet code
- Redundant
- Punctuated
- Universal
- Non-overlapping
Define a codon
Triplet of based in mRNA that codes for a particular amino acid, or punctual signal
Define the term genetic code
The DNA and mRNA base sequence that determine the amino acid sequences in an organisms protein
Define the term Exon
Nucleotide sequence in DNA and pre-mRNA that remains present I. The final mature mRNA after introns have been removed
Define the term intron
Non-coding nucleotide sequence in DNA and pre-mRNA that is removed from pre-mRNA to produce mature mRNA
What happens to RNA in eukaryotes and prokaryotes before it is used to synthesise the polypeptide
In prokaryotes the RNA is mRNA and can be used directly to direct the synthesis of protein
In eukaryotes the initial version of the RNA is pre-mRNA which is longer than the final mRNA :: introns (some sequences of bases) have to be removed
How are introns removed from pre-mRNA in Eukaryotic cells
Introns are cut out of the pre-mRNA using endonucleases and the sequence left are exons which are joined together or spliced with ligases
LOOK AT DIAGRAM ON PAGE 99 IF CONFUSED
What are the 2 main process in protein synthesis
Transcription and translation
What is transcription
A segment of DNA acts as a template to direct the synthesis of a complementary sequence of RNA with the enzyme RNA polymerase.
What is translation
The sequence of codons on the mRNA is used to assemble a specific sequence of amino acids into a polypeptide chain, at the ribosomes
Where does transcription occur?
At the nucleus
Summarise the process of protein synthesis
DNA —> transcription in nucleus —> mRNA —> translation at ribosome —> polypeptide chain
Describe the series of events that occur in transcription up until the formation of mRNA
- Enzyme DNA helicase breaks hydrogen bonds in DNA molecule causing 2 strands to separate exposing nucleotide bases
- Enzyme RNA polymerase binds to the template strand of DNA at beginning of the sequence to be copied
- Free complimentary RNA nucleotides align opposite the template strand
- RNA polymerase moves along DNA forming bonds growing the RNA strand.
- Causes synthesis is mRNA alongside the unwound portion of DNA
Describe the series of events in transcription that occur after mRNA is formed
6-behind the RNA polymerase the DNA strands rewind to form the double helix
7-RNA polymerase separates from the template when it reaches ‘stop’ codon
8-production of the transcript is complete and the newly formed RNA detached from the DNA
LOOK AT DIAGRAM IN BOOK PAGE 100
Which base is missing in RNA?
What is it replaced with?
No thymine in RNA
Replaced by Uracil
What is the purpose of the mRNA produced?
To carry the genetic information originally held in the DNA through the nuclear pore to a ribosome in the cytoplasm
What is the purpose of the codons on the mRNA as part of translation?
They are used to generate a specific set of amino acids, forming a polypeptide
Where does translation take place?
What other aspect is vital for translation?
Translation takes place at the ribosome and it involves the use of tRNA (transfer RNA)
What is the purpose of the large subunit of a ribosome in translation.
The larger subunit has 2 sites for the attachment of tRNA molecule so 2 molecules are associated with a ribosome at any 1 time
What is the purpose of the small subunit of a ribosome for translation
Smaller subunit brings to the mRNA
Describe the process of initiation as part of translation
1) initiation -a ribosome attaches to a ‘start’ codon at one end of mRNA molecule
2) first tRNA (with anticodon complimentary to first codon on the mRNA) attaches to ribosome
3) 3 bases of the codon on the mRNA bond to 3 complementary bases of the anticodon on the tRNA with hydrogen bonds
4) second tRNS, with anticodon complementary go the second codon on the mRNA attaches to the other attachment site and the codon and anti-codon bond with hydrogen bonds
Describe the process of elongation as part of translation
1) two amino acids are close for a ribosomal enzyme to catalyse the formation of a peptide bond between them
2) first tRNA leaves the ribosome, leaving its attachment site vacant, it returns to the cytoplasm and bunds with another copy of its specific amino acid
3) ribosome moves one codon along the mRNA strand
4) Next tRNA binds
Describe the process of termination
1) the sequence repeats until a ‘stop’ codon is reached
2) the ribosome (mRNA) polypeptide complex separates
3) normally several ribosomes bind to a single mRNA strand at a given point
4) Each ribosome produces a polypeptide, so several can be made at once
What is a polysome?
An mRNA strand which has several ribosomes attached reading the coded information at the same time
If the DNA triplet is CCC what is the mRNA codon and anticodon on the tRNA present
MRNA codon = complimentary to DNA = GGG
Anticodon on tRNA = complimentary to mRNA codon = CCC
If the triplet code GAG is the DNA triplet, what is the mRNA codon and Anticodon present of tRNA
mRNA = complimentary = CUC
Anticodon tRNA = complimentary to mRNA = GAG
Describe what happens after the tRNA is released from the ribosome
It is free to collect another amino acid from the amino acid pool In the cytoplasm.
What is ‘amino acid activation’
The idea that energy is required to attach the amino acid to the tRNA
What is the one gene-one polypeptide hypothesis
The idea that a gene is now defined as a sequence of DNA bases that codes for 1 polypeptide
What is ‘post-translational modification’
The modification of a polypeptide chain
Give examples of some post-translational modification
Adding carbohydrate making glycoproteins
Adding lipids making lipoproteins
Adding phosphate making phospholipids-proteins
How are the polypeptides changed after translation and where?
Polypeptides made on the ribosomes are transported through cytoplasm to the Golgi body. Sometimes the primary structure is function by normally the polypeptide is folded into secondary, tertiary or quaternary structures
Give an example of a highly modified protein
- Haemoglobin
- Each polypeptide has a helix regions and a tertiary structure
- four polypeptides are combine to form a quaternary structure
- further modified by combination with four non-protein game groups
Give 2 reasons why tRNA is important
Important as it carried information in the anticodon and it carried the specific amino acid to be incorporated into a growing polypeptide chain
