nucleic acids Flashcards
what are DNA and RNA made up of
monomers called nucleotides
what is a nucelotide
contains a phosphat group, nitrogen-containibg organic base and pentose (either ribose/RNA or deoxyribose/ DNA)
what are the two groups of organic bases
- pyrimidines- single ring
- purines- double ring
what are the 4 nitrogenous bases found in DNA
- guanine (purine)
- cytosine (pyrimidine)
- adenine (purine)
- thymine (pyrimidine)
what is different about the nitrogenous bases in RNA
thymine is replaced by uracil
what does ATP stand for
adenosine triphosphate
is ATP a nucleotide
yes
what is the structure of ATP
a ribose sugar joined to the adrenine base with 3 phosphate groups attached
how is energy released from ATP
- when the high energy bond between the 2nd and 3rd phosphate group is broken via hydrolysis by the enzyme ATPase
- adenosine diphospahte is formed (ADP)
how much energy is released when ATP turns to ADP
30.6 KJ
is ATP to ADP reversible
yes but it requires energy from respiration of glucose to reform bond
ATP hydrolysis equation
ATP –> ADP+ pi (inorganic phosphate) + 30.6 KJ energy
what is the structure of ADP
2 phosphates, ribose, adenine
what are the advantages of ATP
- energy released quickly from one step and involves one enzyme
- energy is release in small amounts
- its universal currency- common source of energy
what are the roles of ATP
- used in many anabolic reactions
- active transport
- muscle contraction
- nerve impulse transmission
what is an exergonic reaction
can occur without energy
what is an endergonic reaction
does require energy
what is the structure of DNA
single strand
- two polynucleotide strands are arranged into a double helix
- first, a dinucleotide is formed when a condensation reaction occurs between two nucelotides
- the 5th carbon atom of the deoxyribose sugar joins to 3rd carbon arom of the deoxyribpse sugar above it via a phosphate moelcule - this builds a single DNA strand
whats the structure of DNA double strand
-DNA is formed from two strands which run anti-parallel to eachother
- held together with hydrogen bonds between complementary bases
- forms a double helix
which bases are complementary
guanine froms hydrogen bonds with cyosine
adenine form hydrogen bonds with thymine
are the hydrogen bonds between bases strong
hydrogen bonds are weak but due to so mnay makes it very strong
how do you extract DNA
- via grinding up cells with ice cold water and washing up liquid
- soap dissolves phospholipid membrane
- protease will digest remaining cellular enzymes and the histones that DNA is wound around
- add ethanol to salt present to cause DNA to precipitate out the solution
what are the types of RNA in protein synthesis
mRNA
rRNA
tRNA
what is mRNA
- a single stranded molecule typically 300-2000 nucleotides long
- produced in nucleus using one DNA strands as a template during transcription
what is rRNA
forms ribosomes with the addition of protein
what is tRNA
- small molecules that wind itself into a cloverleaf shape
- it has anticodons at one end and amino acids at the other
- it transfers the correct amino acid to the growing polypeptide during translation
what are the functions of DNA
- proteins synthesis- the sequence of bases in one strand caled the template strand, determines the order of amino acids in the polypeptide
- replication- when cells divide, a complete copy of DNA needs to be made. both DNA strands seperate and each strand acts as a template to synthesise a complementary strand
what are the theories for how DNA replicates
- conservative replication
- semi-conservative replication
- dispersive
what is conservative replication
original parent double-stranded moelcules is conserved and a new double stranded molecule synthesised from it
what is semi-conservative replication
parental strand separate and each strand acts as a template to synthesise a new strand. the new model consists of one original parent strand and one newly synthesied strand
what is dispersive
the newly synthesised molecules contain fragments from the original parent strand and newly synthesised DNA
what are the stages of semi-conservative DNA replication
- DNA helicase breakes the hydrogen bonds bewteen the bases causing the double helix to unwind and seperate into 2 strands
- the exposed bases bind to free floating nucelotides in the nucleoplasma
- DNA polymerase binds the complementary nucelotides (forming the phosphodiester bond)
- one strand acts as the template for the newly synthesised DNA contains one parent strand and a complementary newly synthesised strand
what is apart of the code
the sequence of nucleotide bases
what is a triplet code/codon
each code has three letters which codes for a specific amino acid
what is a degenerate code
that different codons can code for the same amino acid
what is a one gene
starts the DNA transcription
where does transcription and translation happen in protein synthesis
- transcription- nucleus
- translation- ribosomes
- post translational modification- gologi body
what is transcription
DNA acts as a template for the production of mRNA
what is the process of transcription
- DNA helicase breaks H bonds between complementary bases in the gene to be transcribed.
- RNA polymerase binds to the template strand. Free RNA nucleotides bind with H bonds to their exposed complementary bases
- MRNA produced is complementary to the template strand
- DNA rewinds
- The mRNA molecule leaves though nuclear pore into the cytoplasm where it attached to ribosomes
what happens in eukaryotes after the mRNA leaves the nucelus in transcription
- introns are present within many genes so are also transcribed producing mRNA
- the coding regions are exons
- the pre-mRNA is spliced to remove the non-coding regions before passing to the ribosomes
what happens in prokaryotes after the mRNA leaves the nucelus in transcription
- the DNA doesnt contain introns so the mRNA is produced directly from the DNA template
what is translation
involves converting the codons on the mRNA into a sequnence of amino acids called polypepetides
what is the structure of tRNA
- at one end of tRNA, there are 3 exposed bases called anticodons, these are complementary to the mRNA codom
- at the opposite end of tRNA, is an amino acid attachment site where the relevent amino acid is found. the attachment is called amino acid activation and needes ATP
what is the process of translation
- initatin- ribosome attcahes to the start codon
- tRNA molecule with a complementary anticodon to the first codon binds to the first attachment sit of ribsosome
- a second tRNA molecule joins to the second attachment site and a ribosomal enzyme catalyses the formationof a peptide bond between the two amino acids. this is elongation
- the first tRNA molecules is released and the ribosome now moves one codon long the mRNA which exposes a free attcahment sire and another tRNA moelcule joins and process in repeated
- this repeats until a stop codon is reached when the polypeptide is released-called termination
- usually ribosomes bind to single mRNA strand at the same time- called polysome
why is post translation modification needed
to produce a protein with a secondary, tertiary, quaternanry structure
- occurs in golgi body
- modifciations also occur to produce molecules such as glycoproteins, lipoproteins and complex quaternary structures like haemoglobin
how does haemoglobin formed
2 alpha chains and 2 beta chains need to be assembled together with iron as a prosthetic group
what is a polysome
a group of ribosomes bound to an mRNA molecule like “beads” on a “thread”
what is the function of a polysome
allow for the synthesis of several polypeptides concurrently on the same mRNA molecule.
What organism did the meselson and stahl experiment use
Ecoli
What’s the method for the Meselson and Stahl experiment
- Grow E-Coli in a test tube containing heavy nitrogen (N15) for several generations. This incorporates N15 into the DNA, making it denser than normal DNA which contains N14
- They then extract the DNA and separate it using a centrifuge. This produces a single band of DNA at a high density
- Transfer the bacteria to a test tube containing only N14 and allow them to replicate for one round
- After the first round of replication, extract the DNA and centrifuge it. The DNA will form an intermediate-density band, indicating that each DNA molecule has one old (^15N) strand and one new (^14N) strand
- After a second round of replication in ^14N, centrifuge the DNA again. This time, two bands are observed: one at the light density (all ^14N) and one at intermediate density (one strand ^15N, one strand ^14N).
What were the results of the Meselson and Stahl experiment
- After one replication round in ^14N: All the DNA had one heavy strand and one light strand (intermediate density).
- After two replication rounds in ^14N: Half the DNA molecules were light (both strands ^14N), and half were intermediate (one strand ^15N, one strand ^14N).
The results supported the semi-conservative model of DNA replication. This means that during replication, each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.
