3.1.5 - Nucleic acids are important information-carrying molecules Flashcards
what are DNA and RNA both types of?
nucleic acid
what does DNA stand for?
deoxyribonucleic acid
what is DNA used for?
to store your genetic information
what does RNA stand for?
ribonucleic acid
what is the RNA structure similar to?
similar in structure to DNA
RNA function
transfer genetic information from the DNA to the ribosomes.
RNA and ribosomes
ribosomes read the RNA to make polypeptides during translation
what are molecules of DNA and RNA polymers of?
molecules of DNA and RNA are polymers of nucleotides
what components make up a nucleotide?
- pentose sugar (5 C atoms)
- a nitrogen containing organic base
- phosphate group
what forms when many nucleotides join together
many nucleotides join together to form polynucleotide strands (or chains)
how do the nucleotides join up to form a polynucleotide?
the nucleotides join up via a condensation reaction
condensation reaction forming polynucleotides
condensation reaction between the phosphate group of one nucleotide and the sugar of another
bond formed in condensation reactions to form polynucleotides
this forms a phosphodiester bond (phosphate group and 2 ester bonds). chain of phosphates and sugars is known as the sugar-phosphate backbone
DNA structure
double helix structure
what are the strands in the DNA double helix
polynucleotides
DNA’s structure and use
DNA molecules are very long/coiled up very tightly so lots of genetic information can fit into a small space in the cell nucleus
DNA nucleotide structure
a DNA nucleotide is made from a phosphate group, the pentose sugar deoxyribose and a nitrogen containing organic base
DNA nucleotide structure :
sugar/phosphate
each DNA nucleotide has the same sugar and phosphate
DNA nucleotide structure :
nitrogen containing organic base
the organic base can either be adenine (A), thymine (T), guanine (G) or cytosine (C)
what do 2 DNA polynucleotide strands join together by
2 DNA polynucleotide strands join together by hydrogen bonds between the bases
what is complementary base pairing
each base can only join with one particular other base = complementary base pairing
what are the complementary base pairs in DNA?
adenine pairs with thymine
cytosine pairs with guanine
what does complementary base pairs result in, in terms of amount of bases in DNA
there will always be equal amounts of adenine and thymine and equal amounts of cytosine and guanine
how many hydrogen bonds form between the complementary bases pairs in DNA?
- two hydrogen bonds form between adenine and thymine
- three hydrogen bonds form between cytosine and guanine
RNA structure
RNA is made of nucleotides that contain a sugar, a phosphate group and one of four different bases
RNA structure
what do the nucleotides form
the nucleotides form a polynucleotide strand with a sugar-phosphate backbone
RNA structure
what is the sugar in RNA nucleotides
the sugar in RNA nucleotides is a ribose sugar which is a pentose sugar
RNA structure
bases
Uracil (U, a pyrimidine) replaces thymine as a base. Uracil always pairs with adenine in RNA
RNA structure
polynucleotide strands
nucleotides form a single polynucleotide strand, not a double one
RNA structure
RNA strand length
RNA strands are much shorter than most DNA polynucleotides
why did scientists initially have doubts about DNA carrying the genetic code
DNA was 1st observed in the 1800s, lots of scientists then doubted it could carry the genetic code as it had a relatively simple chemical composition
what did some scientists initially think carried genetic code
some scientists thought genetic information must be carried by proteins which are much more chemically varied
when was it discovered that DNA was the carrier of the genetic code
by 1953, experiments had shown that DNA was the carrier of the genetic code
when was DNA’s double helix structure discovered
in 1953, Watson and Crick discovered DNA’s double helix structure
why does DNA replicate
DNA copies itself before cell division so that each new cell has the full amount of DNA
what is the name for the DNA copying itself before cell division
it is called semi-conservative replication
why is it called semi-conservative replication
as half of the strands in each new DNA molecule are from the original DNA molecule
what does the semi-conservative replication of DNA ensure
means there’s genetic continuity between generations of cells
what happens in the 1st stage of DNA replication?
enzyme DNA helicase breaks the hydrogen bonds between bases on the 2 polynucleotide DNA strands. this makes the helix unwind to form 2 single strands
what happens in the 2nd stage of DNA replication?
each original strand acts as a template for a new strand. complementary base pairing means that free floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand - A with T, C with G
what happens in the 3rd stage of DNA replication?
condensation reactions join the nucleotides of the new strand together, catalysed by the enzyme DNA polymerase. hydrogen bonds form between the bases on the original and new strands. each new DNA molecule contains 1 strand from the original DNA molecule and 1 new strand
3’ (3 prime) and 5’ (5 prime) ends of DNA
each end of a DNA strand is slightly different in its structure, one end is called the 3’ end and the other is called the 5’ end
the action of DNA polymerase
in DNA replication, DNA polymerase’s active site is only complementary to the 3’ end of the newly forming DNA strand, so the enzyme can only add nucleotides to the new strand at the 3’ end so the new strand is made in a 5’ to 3’ direction and the DNA polymerase moves down the template strand in a 3’ to 5’ direction
DNA polymerase working on a double stranded DNA molecule
as the strands in the double helix are antiparallel, the DNA polymerase working on 1 of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand
who came up with the theory of semi-conservative DNA replication?
watson and crick
what validated watson and crick’s theory of semi-conservative DNA replication?
Meselson and Stahl’s experiment a few years later validated their theory
