UWCSEA - IB Biology 2023 - A1.2 - Nucleic acids

A1.2.1 - What is the genetic material of all living things?

DNA; (Deoxyribonucleic acid);

however some viruses use RNA; but are not considered living;

A1.2.2—What is a nucleotide? What are the components of a nucleotide?

Nucleotides are the monomer that form nucleic acids;

Nucleotides consist of three parts;

A five-carbon sugar called a pentose; either deoxyribose or ribose;

A negatively charged phosphate group;(Which is acidic);

and a base that contains nitrogen;

A1.2.2 How can we draw a representation of a nucleotide?

A1.2.3—What forms the "backbone" of DNA and RNA?

Sugar-phosphate bonding;

makes a continuous chain of covalently bonded atoms in each strand of DNA or RNA nucleotides;

which forms a strong "backbone" in the molecule;

A1.2.3 - How can we draw a representation of the backbone of DNA/RNA?

Label the phosphate, deoxyribose sugar and base

A1.2.4— What forms the basis of the code in DNA and RNA? What are the names of these?

The nitrogenous bases;

adenine, cytosine, guanine, cytosine and thymine;

A1.2.5—How is an RNA polymer formed?

RNA is formed by condensation of nucleotide monomers;

water is removed;

using enzymes;

the strand is a single strand of nucleotides;

A1.2.6—What is the structure of the DNA double helix?

draw the two strands antiparallel, but are not required to

draw the helical shape;

show adenine (A) paired with thymine (T), and guanine (G) paired with cytosine (C)

A1.2.7—What are the between DNA and RNA?

number of strands present: DNA is double stranded, RNA is single stranded;

Deoxyribose in DNA, versus ribose in RNA;

Deoxyribose has an only one OH group at the bottom;

Students should be

familiar with examples of nucleic acids.

A1.2.8— What is complementary base pairing? What is it's role in allowing genetic information to be copied accurately?

complementary base pairing is the fact that one base only pairs with one other base;

the basis of complementarity;

e.g. adenine and thymine; form 2 hydrogen bonds between each other;

whereas guanine and cytosine; form 3 hydrogen bonds;

so what is on one strand determines what can pair on the other;

therefore one base determines which base can bond to it;

A1.2.9— Why does DNA have almost unlimited storage capacity (in terms of information)?

because there are 4 distinct bases;

which can be in any order;

and the length of DNA can be very long;

leading to a huge number of possible combinations;

giving it enormous capacity for storage in a very small molecule;

A1.2.10 - How is DNA evidence of a universal common ancestry

The DNA code is common across all organisms;

using the same 4 bases and coding for the same amino acids (with a couple of exceptions);

suggesting a common ancestry for all species;

HL ONLY - A1.2.11— How does DNA and RNA have a direction? What is it?

the carbons in the sugar in DNA and RNA can be labelled;

from 1 to 5;

the top of the sugar molecule has carbon 5;

the bottom left has carbon 3;

new DNA and RNA bases are added to the 3' (3 prime) end;

creating new sugar-phosphate linkages;

HL ONLY - A1.2.12—What are purines? What are pyrimidines? How does their bonding lead to stability of DNA?

Purines are bases with two rings;

Guanine and Adenine;

remember Pure As Gold;

Pyrimidines only have one ring;

Thymine and cytosine; and uracil;

remember pyramids have one structure (not two);

One purine has to bond with only one other pyrimidine;

Adenine-thymine (A-T) and cytosine-guanine (C-G) pairs have equal length;

so the DNA helix has the same three-dimensional structure, regardless of the base sequence.

HL ONLY - A1.2.13—What are nucleosomes? What is their structure?

Nucleosomes help to package DNA;

and regulate supercoiling;

A nucleosome consists of DNA wrapped around eight histone held together by an additional histone protein attached to linker DNA;

HL ONLY - A1.2.14—What was the Hershey-Chase experiment? What were the conclusions of it?

The Hershey and chase experiment provided evidence that DNA and not protein is the molecule of inheritance;

they used radioactively labelled 35 S (sulphur is normally 32 S) used;

in a medium to grow phage (viruses that infect bacteria);

this meant phage created radioactive protein coats;

when bacteria were infected with the phage the radioactive protein was left outside the bacteria;

no radioactive phage were produced;

however, they repeated the experiment with radioactively 32 P (phosphorous is normally 30 P) was used to label DNA in the phages;

when infected, the bacteria then had radioactively labelled 32 P inside them and the phage produced after also contained the 32 P;

these were found in the pellet (because they are heavier;

therefore, DNA is passed on and used to created new phage and is the molecule of inheritance;

HL ONLY - A1.2.15—What was Chargaff's data? What did it suggest?

Chargaff's discovered a ratio of bases in DNA;

that C and G have same percentage;

and A and T have same percentage;

therefore this suggested they pair together;

this falsified an idea about the tetranucleotide hypothesis that there was a repeating sequence of the four bases in DNA;

it shows how the "problem of induction" is addressed by the "certainty of falsification";