Nucleic Acids Flashcards
What are nucleic acids?
Large molecules in the cell nuclei
What are the two types of nucleic acids?
DNA and RNA
What are the roles of both DNA and RNA
Storage,transfer of genetic information and the synthesis of polypeptides
What elements do nucleic acids contain?
Carbon, hydrogen, oxygen, nitrogen and phosphorus
What is an individual nucleotide composed of?
- a pentose monosaccharide (sugar), containing five carbon atoms
- a phosphate group, PO42_^, an inorganic molecule that is acidic and negatively charged
- a nitrogenous base - a complex organic molecule containing one or two carbon rings in its structure as well as nitrogen
How are nucleotides linked together?
Condensation reactions
What is the polymer of nucleotides called?
Polynucleotides
Where are phosphodiester bonds formed in a polynucleotide?
The phosphate group at the fifth carbon of the pentose sugar (‘5) of one nucleotide forms a covalent bond with the hydroxyl (OH) group at the third carbon (3’) of the pentose sugar of an adjacent nucleotide
How are phosphodiester bonds broken?
hydrolysis which releases the individual nucleotides
Why is DNA replication necessary?
To ensure we have the correct amount of DNA before cell division
What does DNA helicase do?
unwinds double helix
What does DNA polymerase do?
joins one nucleotide to the next
What does the term lagging mean in DNA replication?
the original strand running 5’ to 3’
What does the term leading mean in DNA replication?
the original strand running 3’ to 5’
What does DNA ligase do?
joins together small sections of DNA
What are Okazaki fragments?
separated sections of DNA
What are the purine bases?
Guanine and adenine
What are the complimentary base pairs?
Adenine and thymine, cytosine and guanine
What types of bonds exist between base pairs?
hydrogen bonds
What type of bonds exist between phosphate and sugar in a nucleotide?
phosphodiester, which is a type of covalent bond
How many hydrogen bonds are between a thymine and an adenine?
2
What is in the backbone of a DNA double helix?
sugar and phosphate
What are the types of RNA?
mRNA- messenger RNA
tRNA- transport RNA
rRNA- ribosome RNA
what does the semi-conservative replication of DNA do?
involves separation of the DNA strands followed by replication of each strand separately to produce DNA, which is half parental and half new
what is mRNA?
a copy of DNA and a code for the amino acids
what is a triplet code?
every 3 bases will code for one amino acid
what is the genetic code?
the way in which DNA codes for amino acids within organisms
what is the universal code?
all organisms use the same triplet for the same amino acids
what is the degenerate code?
some amino acids are coded for by more than one triplet
what is the non overlapping code?
the code is always read from the same starting point, each base is only read once in the sequence
what is the triplet code?
when bases are read three times
what is transcription in proteinsynthesis?
making a copy of the DNA using mRNA
what is translation in proteinsynthesis?
translating mRNA code into a sequence of amino acids
what is the process of transcription in proteinsynthesis?
1) hydrogen bonds break between complementary bases and DNA unzips (catalysed by DNA helicase)
2) expose sense strand (coding which runs 5’ to 3’) and anti sense strand (templates which run 3’ to 5’)
3) free nucleotides bind to exposed bases on antisense strand of DNA by complimentary base pairing
4) RNA polymerases catalyses formation of phosphodiester bonds between RNA nucleotides
5) at the end of the gene, mRNA is released from DNA and passes out of the nucleus through nuclear pore into cytoplasm
6) resulting mRNA is a copy of the sense strand, aside from substitution of U for T.
what is the process of translation?
1) mRNA binds to ribosomes first 6 bases attached to small subunits and exposed to large one
2) second tRNA binds to next codon
3) peptide bonds form between Met and Tyr (enzyme peptidyl transferase in small subunits catalyses this)
4) ribosomes move along mRNA to next codon and tRNA bearing next amino acid joins, peptide bond forms
5) process continues until stop codon reached, no tRNAs carry anticodons for stop codons so polypeptide chain terminates at previous codon. polypeptide is released
during transcription, is the mRNA a copy of the sense or antisense strand?
sense
how many tRNAs fit into a ribosome at one time?
2
why does a stop codon result in termination of the polypeptide chain?
no anticodon exist
where might a polypeptide chain be altered following translation?
golgi apparatus and rough endoplasmic reticulum
what are some similarities between DNA replication and transcription?
- require making a new copy of DNA
- they both occur in the cell nucleus
what are some differences between DNA replication and transcription?
- DNA transcription is involved in conversion of DNA to RNA whereas replication is the process of making another copy of DNA
- transcription makes RNA strands short whereas replication makes DNA strands long
which bonds hold together the nucleotides in the sugar phosphate backbone?
phosphodiester bonds
what are the names of the four bases?
adenine
thymine
guanine
cytosine
what bonds hold together the bases in a double helix?
hydrogen
how many bonds form between cytosine and guanine?
3
how many bonds form between thymine and adenine?
2
describe the role of DNA helicase in DNA replication?
unravels the DNA by breaking down hydrogen bonds between complimentary bases
describe the role of DNA polymerase in DNA replication?
makes DNA by joining one nucleotide to the next
what is a codon?
3 bases on the mRNA- amino acid
