12.3 Nucleic acids Flashcards
what does DNA stand for
deoxyribonucleic acid
what does RNA stand for
ribonucleic acid
DNA and RNA are…
important information carrying molecules
what does DNA do
holds genetic information
what does RNA do
transfers genetic info from DNA to the ribosomes
monomer in DNA
DNA nucleotide: a deoxyribose sugar, a phosphate group and a nitrogen containing base (adenine, cytosine, guanine or thymine)
monomer in RNA
RNA nucleotide: a ribose sugar, a phosphate group and a nitrogen containing base (adenine, cytosine, guanine or uracil)
polynucleotide formation
condensation reaction between 2 or more nucleotide monomers forming a phosphodiester bond
polynucleotide strands are formed when…
many nucleotides link to form a long chain
a phosphodiester bond forms between…
the phosphate group of 1 nucleotide to the 3rd C of the (D/R) sugar in the next nucleotide
what makes a nucleic acid very strong and stable
the sugar-phosphate backbone of the nucleic acid
structure of a DNA molecule
double helix
DNA consists of…
2 polynucleotide chains held together by many weak H bonds between specific complementary base pairings
how many H bonds are formed between Adenine and Thymine
2
how many H bonds are formed between Cytosine and Guanine
3
top of the chain
5’ to 3’
bottom of the chain
3’ to 5’
bonds in the backbone
phosphodiester
bonds that bring both the strands together
H bonds
How do you answer percentage questions DNA
If we are given the % of 1 base, we can use that to work out the % of the other complementary base. And then the % of the 2 other bases.
The sequence of the bases along the nucleotide chain is…
Variable (basis of the genetic code and how info is stored in DNA)
The function of DNA is that it…
Codes for the sequence of amino acids (3 bases = triplet = 1 amino acid).
Long strands of DNA code for…
The primary structure of polypeptide chains and proteins.
What is an mRNA molecule?
A relatively short polypeptide chain, which is normally a single stranded helix.
What is mRNA used to do?
To transfer genetic information from DNA to ribosomes.
Structure of DNA
Structure of RNA
sugar phosphate backbone with bases
DNA consists of…
2 antiparallel nucleotide strands
To make sure the 2 strands remain parallel (the same distance apart)…
Adenine pairs with Thymine and Cytosine pairs with Guanine.
What does it mean when we say the DNA is parallel?
The 2 strands of DNA run in opposite directions.
What does the 5’ and 3’ indicate?
Which carbon is involved in the phosphodiester bond.
If you follow the left hand chain up to the end at the top you would have…
A phosphate group attached to C5 on the deoxyribose sugar.
If you follow it to the other end you would have…
An hydroxyl (OH) group attached to C3 on the received sugar
On the complementary strand…
The top has a 3’ end and the bottom has a 5’ end.
Why is it important that on the complementary end the top has a 3’ end and the bottom has a 5’ end?
- when making proteins (It ensures that only 1 strand is read to make the protein)
- in DNA replication as DNA polymerase only has a complementary AS to the 5’ end (or phosphate group) of the molecule
structure of DNA: sugar-phosphate backbone and double helix structure whats the function
1 provides strength + stability
2 protects (info coded in) the bases
3 protects H bonding between bases
structure of DNA: long/ large molecule whats the function
so stores a lot of info
structure of DNA: helical / coiled structure whats the function
so compact
structure of DNA: base sequence whats the function
allows info to be stored / codes for amino acids and therefore proteins
structure of DNA: double stranded whats the function
so replication can occur semi-conservatively because each strand can act as a template
structure of DNA: complementray base pairing A-T and C-G whats the function
allows accurate replication / identical copies are made (prevents mutations)
structure of DNA: H bonds between bases are weak whats the function
allows for easy strand separation for semi-conservative replication
structure of DNA: many weak H bonds whats the function
so DNA is a strong / stable molecule
why does DNA replication occur
so that when new cells are created in the body they all have the exact same copy of DNA
what method of DNA replication occurs
semi-conservative
what does semi-conservative replication produce
a new molecule of DNA half the molecule is old and half of it is new
what does semi-conservative DNA ensure
that genetic info stays the same between generations of cells
function of DNA helicase
breaks the H bonds between the complementary base pairs so each strand can act as a template
function of DNA polymerase
catalyses the condensation reactions between DNA nucleotides to form the sugar-phosphate backbone of each strand
process of semi-conservative replication
1 enzyme DNA helicase attches and moves along the DNA molecule unwinding the DNA and breaking the H bonds between complementary bases
2 the 2 strands separate
3 each strand acts as a template
4 new DNA nucleotides are attracted to exposed complementary bases on template strands by base pairing a-t + c-g
5 enzyme DNA polymerase joins adjacent nucleotides together through a condensation reaction forming phosphodiester bonds between new nucleotides and water in a 5’ to 3’ direction
6 semi-conservative replication ensures that each new DNA molecule contains an original and a new strand and is identical to the original DNA
why was bacteria used in Meselson and Stahl’s experiment
bacteria was used as it replicated quickly (every 20 minutes)
what were the names of the 3 theories of DNA replication
- conservative
- semi-conservative
- dispersive
conservative model
an entirely new molecule is synthesised from a DNA template (which remains unaltered)
semi-conservative model
each new molecule consists of 1 newly synthesised strand and 1 template strand
dispersive model
new molecules are made of segments of new and old DNA
centrifugation meaning
separates mixtures according to its density
Meselson stahl experiment
1 bacteria grown in 15N medium for many generations (original)
2 bacteria transferred to 14N, allowed to replicate once here for / for 1st gen. DNA extraction and centrifugation
3 bacteria allowed to replicate a 2nd time / for 2nd gen in 14N medium. DNA extraction and centrifugation
4 bacteria allowed to replicate a 3rd time / for 3rd gen in 14N medium. DNA extraction and centrifugation
Meselson stahl experiment summary
- bacteria with 15N containing DNA molecules allowed to replicate their DNA and divide by binary fission multiple times in 14N medium, the formed DNA
- molecules being extracted, centrifugated, and their different masses separated between each round of replication to analyse the distributions of different mass DNA as a result of a particular model of replication.
