Nucleic Acids Flashcards
What elements do all nucleic acids contain?
carbon, hydrogen, oxygen, nitrogen, phosphorous
What are the 2 classes of nucleic acids?
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
What are Nucleic Acids called?
Polynucleotides (they are polymers of nucleotides)
What is the structure of a nucleotide?
an organic base, a pentose sugar, and a phosphate
What does an organic base of a nucleotide contain?
nitrogen, classified as purines (2 rings) or Pyrimidines (1 ring)
What are the purines in DNA and RNA?
Adenine and Guanine
what are the pyrimidines in DNA and RNA?
Cytosine and Thymine in DNA, Cytosine and Uracil in RNA
What are the pentose sugars in DNA and RNA?
deoxyribose in DNA and ribose in RNA
How are the bonds linking the 3 components formed and split?
formed by condensation reactions
split by hydrolysis reactions
How many polynucleotide strands does DNA consist of?
2 it is double stranded
How are nucleotides linked together?
by ‘sugar phosphate’ bonds
How are nucleotide strands joined together
by hydrogen bonds between complementary base pairs
Which nucleotide bases pair together in DNA?
Adenine pairs with Thymine
Guanine pairs with Cytosine
What is the structure of DNA called? and how is it formed?
A double helix
both strands are twisted together and maintained by hydrogen bonds
Who discovered the structural arrangement of phosphate backbones, who got credit?
Rosalind Franklin worked out
Watson and Crick won nobel prize for it in 1962
How large is a polynucleotide?
each one may contain millions of units so its very large
What are the 2 major functions of DNA?
Replication, where DNA copies itself before cell division
Carrying the genetic code ( = information for protein synthesis)
What are the 3 types of RNA?
messenger RNA (mRNA)
transfer RNA (tRNA)
ribosomal RNA (rRNA)
Is Ribose double or single stranded?
single stranded there is no base complimentaries in mRNA
What is a gene?
a section of DNA which codes for the synthesis of a polypeptide/protein
what is mRNA?
a long, single stranded molecule formed into a helix
it is synthesised during transcription
produced in nucleus
What is the function of mRNA?
carries the genetic code from DNA in nucleus to ribosomes in cytoplasm
what is tRNA?
small, single stranded ‘clover leaf’ structure.
(some base pairing G with C, A with U)
free floating in cytoplasm
What is the function of tRNA?
carries amino acids to ribosomes during translation
20 different kinds for 20 different amino acids
What are ribosomes composed of?
a protein and rRNA
What is the function of ribosomes?
site of protein synthesis
What is rRNA?
large complex molecule composed of single & double helices (large subunit with central protuberance and small subunit)
made in nucleolus
both helical and single stranded in places
What are hydrogen bonds in DNA?
weak bonds which hold the 2 strands of the double helix together
What does DNA helicase do?
‘unzips’/ pulls apart hydrogen bonds between the 2 strands of double helix
After DNA helicase has acted on a DNA what happens?
2 exposed strands are produced which act as a template for the formation of a new strand
free nucleotides pair up with the exposed bases
What forms between the complementary base pairs? new strand and old strand
new hydrogen bonds
What does DNA polymerase do?
catalyses the sugar and phosphate groups of adjacent nuclotides condensing
On which strand is only DNA polymerase used on?
leading strand
On which strand is both DNA polymerase and DNA ligase used on?
lagging strand
What happens between lagging and leading strand due to DNA polymerase?
the strands wind back up into the double-helix, which are both identical to the original
synthesises new DNA
How many hydrogen bonds form between bases A and T?
2
How many hydrogen hydrogen bonds form between bases G and C?
3
How are the 2 chains in DNA orientated?
the chains are anti-parallel, one chain runs from C5 to C3 whilst the other runs from C3 to C5
What is transcription?
the process of copying a DNA strand into RNA molecules that can encode proteins
occurs in the nucleus
permits the flow of genetic information (mRNA) carrys from nucleus to the sites of protein synthesis in ribosomes in cytoplasm
involves DNA helicase and polymerase
What is translation?
when tRNA reads the genetic code that is able to pick up specific amino acids and delivers them to the ribosomes where the amino acids may be assembled into proteins according to the instructions carried on messenger RNA
How many genes code for a polypeptide?
1
what are introns?
spaces in gene which do not code for proteins and interrupts the sequence in gene
What are exons?
useful parts of gene that code for will go on to code for proteins
What does mRNA do to introns and exons?
it copies the full gene but then the inrons are spliced out. Resulting mRNA is shorter than the original gene.
What is a codon?
a triplet of bases
What are anticodons?
triplets of bases exclusively found on tRNA, consists of complimentary bases to codon, and allow to code for slection of correct protein for protein synthesis
How many amino acids do we need? how many different combinations of bases do we have?
we need 20 amino acids we can have up to 64 combinations of bases. More than one codon may code for the same amino acids
In transcription how does RNA polymerase work?
as RNA nucleotides align alongside DNA strand
RNA polymerase moves along the DNA forming bonds that add RNA nucleotides, synthesising mRNA
behind RNA polymerase DNA strands rewind to form double helix
RNA polymerase separates forom the template strand when it reaches a ‘stop’ signal
The production od the transcript is complete and the newly formed RNA detaches from the DNA
What are the 3 steps towards translation?
initiation
elongation
termination
What happens in the initiation phase of translation?
a ribosome ‘attaches’ to a ‘start’ codon at one end of the mRNA molecule
The first tRNA, with an anticodon complementary to the first codon on the mRNA attaches to the ribosome. The three bases of the codon on the mRNA bond to the three complementary bases of the anticodon on the tRNA, with hydrogen bonds.
A second tRNA, with an anticodon complementary to the second codon on the mRNA, attaches to the other attachment site and the codon and anti-codon bond with hydrogen bonds
What happens in the elongation phase of translation?
ribosomal enzyme catalyses peptide bond formation between 2 amino acids
first tRNA leaves the ribosome, vacant attachment site. Returns to cytoplasm to bind another copy of its specific amino acid
the ribosome moves one codon along the mRNA strand
the next tRNA binds
What happens in the Termination phase of translation?
the sequence repeats until a ‘stop’ codon is reached
the ribosome - mRNA - polypeptide complex separates
usually several ribosomes bind to a single mRNA strand, each reading the coded information at the same time. Called a Polysome. Each ribosome produces a polypeptide, so several are made at once
What is a polysome?
several ribosomes binding to single mRNA strand, each reading coded information at the same time
What does Meselsohn and Stahl’s experiment prove?
semi-conservative replication
What medium did Meselsohn and Stahl use?
cultured bacteria in a medium containing amino acids made with the heavy isotope 15N
Producing bacteria where DNA contained only 15N
What did the mixing of 15N nitrogen with lighter 14N nitrogen result in?
A new generation is produced, with which they centrifuged, this had a midpoint density (this could imply that one band of DNA was 15N and other was 14N)
What were the results of the second generation of 15N and 14N together?
when centrifuged the midpoint layer appeared again and a layer above, which means its lighter so and was therefore consisting of all 14N isotopes, this was in equal proportion
How did the second generation in Meselsohn and stahl prove semi-conservative replication?
two separate bands ruled out dispersive replication because in dispersive there would always be a mixture of light and heavy in every strand and one band would only form. One parental strand is conserved therefore it is semi-conservative hypothesis proved correct.
