2.3.1(Nucleic acids)

What is a “nucleotide”?

• A molecule consisting of a pentose sugar(deoxyribose or ribose), a phosphate group and a nitrogenous base

What is a “polynucleotide”?

• Large molecule containing many nucleotides that are bonded

What is the name of the bond between nucleotides?

• Phosphodiester bond

State what happens to nucleotides when multiple phosphate groups are present in a molecule?

• They become phosphorylated

Describe the structure of ATP

• ribose pentose sugar

• 3 Phosphate groups

• adenine nitrogenous base

What are the 5 nitrogenous bases?

• Adenine (DNA and RNA)

• Cytosine (DNA and RNA)

• Guanine (DNA and RNA)

• Thymine (DNA)

• Uracil (RNA)

State the difference between purines and pyrimidines?

• Purines:

  • Two rings that contains nitrogen

• Pyrimidines:

  • 1 ring containing nitrogen

Describe the structure of DNA

• It is a polymer made up of monomers of nucleotides

• A DNA molecule consists of 2 polynucleotide strands that run in different directions, described as antiparallel

• The strand of the DNA is a sugar phosphate backbone consisting held by phosphodiester bonds which are strong covalent bonds

• DNA molecules are long and therefore can carry a lot of encoded information

• Between the nucleotides, there are hydrogen bonds that hold the 2 strands together

State the number of hydrogen bonds between both:

• A and T

• C and G

• A and U

• Between A and T, A and U, there are 2 hydrogen bonds

• Between C and G, there are 3 hydrogen bonds

Which bases are purine and which are pyrimidines

• Purines:

  • Adenine and guanine

• Pyrimidines:

  • Thymine, Cytosine and uracil

Explain how hydrogen bonds can be useful during replication

• Because hydrogen bonds are weak, they can easily be broken by enzymes to unzip the strands and separate them to be transcribed and replicated

Explain why a purine and a pyrimidine always pair

• This is so they give equal-sized “rungs” on the DNA ladder

• These rungs can the twist and coil into a double helix which gives the molecule stability

state what is being referred to by the “opposite directions” of the 2 polynucleotide?

• It refers to the direction that the3rd and 5th carbon molecules in the pentose sugar, deoxyribose are facing

Describe how the sugar phosphate back bone is arranged in terms of carbon numbers

• The 5’ end if where the phosphate group is attached to the 5th carbon of the deoxyribose sugar

• The 3’ end is where the phosphate group is attached to the 3rd carbon atom of the deoxyribose

Describe how DNA is organised in eukaryotic cells?

• Most DNA is held in the nucleus

• DNA is tightly wound around histone proteins to form chromsomes

• It is also inside of chloroplasts and mitochondria without histone proteins

Describe how DNA is organised in prokaryotes?

• It is organised in a loop within the cytoplasm, not enclosed in a nucleus

• It is not wound around histone proteins, and is described as naked.