Nucleotides and nucleic acids Flashcards
What is the name of the monomer that forms nucleic acids.
Monomer = Nucleotide
DRAW the general structure of the monomer of nucleic acids and label it.
Check summary sheet 1.5
Name the reaction and the bond formed between to monomers
Condensation reaction forms phosphodiester bonds between nucleotides.
What does DNA stand for?
Deoxyribonucleic acid
DRAW the general structure of DNA and label it
Check summary sheet 1.5
Name the bonds present between the DNA nucleotides?
Phosphodiester bonds
Name the bonds present between the complimentary base pairs?
Hydrogen bonds
Explain how the structure of DNA is related to its functions (mark schemes can vary so write everything!)
Sugar-phosphate backbone –> Gives strength
Helix/Coiling –> Gives it a compact shape
Large Molecule –> Stores lots of information
Sequence of bases –> Allows information to be stored/codes for amino acids
Double helix with many hydrogen bonds –> Makes the DNA molecule stable
Double stranded/Two strands –> BOTH strands can act as templates during semi-conservative replication
Double helix –> Prevents the code being corrupted
Hydrogen bonds between the bases are weak and easily broken –> Allows the strands to be separated for replication and also for protein synthesis
Complementary base pairings –> Allows accurate replication
What is meant by specific base pairing?
Each base is complementary to one other base – this is the one that it binds to.
Guanine and cytosine are complementary to each other and therefore ONLY bind to each other
Adenine and thymine are complementary to each other and therefore ONLY bind to each other
What do we mean by ‘the strands are anti-parallel’?
The strands go in opposite directions. One strand goes in the 5’to 3’ direction the other goes in the 3’ to 5’ direction
Describe the differences between DNA and RNA (5 marks)
DNA has A,T,C,G bases whereas RNA has A,U,C,G
DNA has a deoxyribose sugar whereas RNA has a ribose sugar
DNA is double stranded wheras RNA is single stranded
DNA is a large polymer RNA is a short polymer
DNA holds genetic information in the nucleus whereas RNA transports genetic information to the ribosome
Describe the differences between DNA in prokaryotes and Eukaryotes
DNA in eukaryotes is coiled up around proteins called HISTONES whereas the DNA in prokaryotes is not
DNA in eukaryotes is linear whereas DNA in prokaryotes is circular
DNA in eukaryotes is found in a nucleus, whereas DNA in prokaryotes is in the cytoplasm
A gene is a section of DNA located at a particular site on a DNA molecule, called its ______?
Locus
What are genes?
Genes are a specific sequence of bases which can code for the amino acid sequence of a polypeptide or functional RNA (E.G. ribosomal RNA and tRNA)
What is a triplet code?
3 bases on DNA are called a TRIPLET CODE 🡪 3 bases CODE for 1 amino acid. Each triplet codes for a SPECIFIC amino acid.
What is the link between DNA bases, amino acids and a protein?
A sequence of bases codes for a sequence amino acids to form a polypeptide chain which can fold into a protein.
What are introns?
non-coding DNA within a gene
what are Non-coding multiple repeats?
non-coding DNA found between genes
What are exons?
the coding section of a gene (i.e. the bit that codes for amino acids)
Define universal
each triplet codes for the same amino acids in all organisms
Define Non-overlapping
each base is only used in one triplet code
Define Degenerate
Some amino acids are coded for by more than 1 triplet code/codon
Define genome
the complete set of genes in a cell
Why might changing the base sequence of a gene lead to a non-functional protein being formed?
Different base sequence 🡪 codes for a different sequence of amino acids (different primary structure) 🡪 Different hydrogen, ionic and disulphide bonding between R-groups 🡪 different tertiary structure 🡪 protein is a different shape so no longer functions
Describe the process of DNA replication
DNA helicase causes H-bonds to break and strands to separate
Both strands act as templates
Free DNA nucleotides attach to each strand by
complementary base pairing (A binds with T and G binds with C)
H-bonds form between the complementary base pairs
DNA polymerase joins nucleotides on the new strand together (causes the covalent bond between the sugar and phosphate to form)
Why is DNA replication described as being ‘semi-conservative’?
Because each new double helix is made of one old strand and one new strand of DNA
Meselson and Stahl grew bacteria on a medium containing N15.. Why is this Nitrogen different to ‘normal’ nitrogen and why was it used? (What was the Nitrogen incorporated into in the bacteria?)
It is an isotope of nitrogen so it is more dense. This nitrogen was incorporated into the nitrogenous bases in the DNA
They then moved the bacteria to a medium containing N14. When they took a sample of DNA from these bacteria after they had grown on the new medium for 1 generation, what did they notice about the density of the DNA compared with DNA from the original bacteria? Explain your answer.
The DNA from the bacteria which had grown on N14 for one generation was less dense than the DNA from bacteria that had only grown on N15.
After a second generation on the N14 medium they found that they had DNA double helices of 2 different densities. Explain their finding:
Some of the DNA molecules were made of one strand of DNA that contained N15 and one strand of DNA that contained N14. Some of the DNA molecules were made of DNA in which both strands contained N14. These DNA molecules (with only N14 ) were less dense
What chemical processes produces ATP?
Respiration
What does ATP stand for?
Adenosine triphosphate
Draw the molecule of ATP and label it
Check ss 1.6
Write an equation to show how ATP releases energy
H2O + ATP –> <– ADP + Pi
What is the name of the enzyme which catalyses the hydrolysis of ATP?
ATP hydrolase
What does ADP stand for?
Adenosine diphosphate
What is Pi? What happens to the ‘Pi’ that is released? What is its function in cells?
‘Pi’ is inorganic phosphate. It is the phosphate ion (which has the formula PO43-)
Phosphate can join onto molecules to make them more reactive
It has lots of uses in cells, e.g.
In the phosphate-sugar backbone of DNA and RNA
In phospholipids
During which processes is ATP resynthesized? What sort of reaction is this? What is the name of the enzyme which catalyses the reaction?
ATP is synthesized primarily during respiration (also during photosynthesis)
This is a condensation reaction
The reaction is catalysed by ATPsynthase
What are the key features of ATP which make it an excellent source of energy for cellular reactions? MEMORISE THIS!!!!!
It releases energy in small amounts
It is an immediate source of energy as it can release energy in just one step by breaking just one bond so it makes energy available rapidly
It can add a phosphate group (phosphorylates) other molecules to make them more reactive
It can be regenerated
How is the structure of mRNA different to the structure of tRNA
- mRNA does not have hydrogen bonds / base pairing, tRNA does;
OR
mRNA is linear / straight chain, tRNA is cloverleaf; - mRNA does not have an amino acid binding site, tRNA does;
- mRNA has more nucleotides;
accept mRNA is longer - (Different) mRNAs have different lengths, all tRNAs are similar / same length;
- mRNA has codons, tRNA has an anticodon;
Contrast the structures of DNA and mRNA
DNA double stranded/double helix and mRNA single-stranded;
DNA (very) long and RNA short;
Thymine/T in DNA and uracil/U in RNA;
Deoxyribose in DNA and ribose in RNA;
DNA has base pairing and mRNA doesn’t/ DNA has hydrogen bonding and mRNA doesn’t;
DNA has introns/non-coding sequences and mRNA doesn’t;
Describe and explain how the structure of DNA results in accurate replication. [6]
1 two strands therefore semi-conservative replication (possible);
2 base pairing/hydrogen bonds holds strands together
3 hydrogen bonds weak/easily broken, allow strands to separate;
4 bases (sequence) (exposed so) act as template /can be copied;
5 A with T, C with G / complementary copy;
6 DNA one parent and one new strand;
Describe the role of two named enzymes in the process of semi-conservative replication of DNA [3]
- (DNA) helicase causes breaking of hydrogen/H bonds (between DNA strands);
Reject ‘helicase hydrolyses hydrogen bonds’. - DNA polymerase joins the (DNA) nucleotides;
Reject if suggestion that DNA polymerase joins the complementary nucleotides or forms H bonds.
Reject if joining RNA nucleotides or forming RNA.
- Forming phosphodiester bonds;
explain why new nucleotides can only be added in a 5’ to 3’ direction.
DNA polymerase;
(Which is) specific;
Only complementary with/binds to 5’ end (of strand);
Shapes of 5’ end and 3’ end are different;
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells. [5]
Comparisons
Nucleotide structure is identical;
Nucleotides joined by phosphodiester bond;
OR
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Accept shorter than nuclear DNA/is circular not linear/is not associated with protein/histones unlike nuclear DNA;
Contrasts
Eukaryotic DNA is longer;
Eukaryotic DNA contain introns, prokaryotic DNA does not;
Eukaryotic DNA is linear, prokaryotic DNA is circular;
Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;
