Chapter 3 Nucleic Acids Flashcards
What are the two types of nucleic acids, what are their roles
The two types are DNA and RNA, and they have roles in storage and transfer of genetic information and the synthesis of polypeptides. Basis for heredity.
What elements do nucleic acids contains and what is the polymer made of
Carbon, hydrogen, oxygen, nitrogen and phosphorous. The polymer is made of nucleotide monomers.
What are the three individual components of a nucleotide.
A pentose monosaccharide (sugar), containing five carbon atoms
a phosphate group, 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.
The linking for Nucleotides, How does it happen, what bonds are made.
Linked by condensation reactions to form a polynucleotide. The phosphate group of 5th carbon of the pentose sugar, of one nucleotide forms a covalent bond with the hydroxyl group at the third carbon of the pentose sugar of an adjacent nucleotide forming a phosphodiester bond.
This forms a strong backbone with a base attached to each sugar. The phosphodiester bonds are broken by hydrolysis, the reverse of condensation.
Deoxyribonucleic acid (DNA)
it is a sugar with one fewer oxygen atoms than ribose.
The nucleotide in DNA each have one of four different bases. This means there are four different DNA nucleotides. The four bases can be divided into pyramidines - T and C and Purines - A and G.
What is the difference between pyrimidines and Purines
Pyrimidines are the smaller bases which contain single carbon ring structures - Thymine and cytosine.
Purines are the larger bases, which contain double carbon structures - Adenine and Guanine.
The double helix structure.
DNA molecules can vary in size from a few nucleotides to millions of nucleotides. It’s made of two strands which are held together through hydrogen bonds and then coiled up.
Each strand has a 5’ end of a phosphate group and a 3’ end of the hydroxyl group at the other end. They are arranged so they run in opposite direction so they are antiparrallel.
The pairing between the strands allows easy copying and transcription.
Where is the structure of the nucleotide
The backbone has the phosphate group and pentose sugar and the strand has the pair of bases.
Base pairing rules
Adenine and Thymine are only able to make two hydrogen bonds and always join together whereas cytosine and guanine are able to make three hydrogen bonds so they bind together. This means a small pyrimidine base always binds to a large purine base.
This means the distance between the strands is always the same so they strands are parrallel.
The base pairing means that the DNA always has the same proportion of A and T aswell as C and G
Ribonucleic acid (RNA)
has a role in the transfer of genetic information from DNA to the proteins that make up the enzymes and tissues of the body. The DNA of each eukaryotic chromosome is very long, so is unable to leave the nucleus which means a really short strand of DNA is transcribed onto a short messenger RNA molecule (mRNA). Each individual mRNA is therefore much shorter than the whole chromosome of DNA.
RNA forms polymers the same way with phosphidiester bonds in condensation reactions. The RNA polymers are small enough to leave the nucleus and travel to the ribosome, where they are useful in protein synthesis.
After proteins synthesis the RNA molecules are degraded in the cytoplas. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.
DNA extraction procedure
Grind the sample in mortar with pestle - breaks down the cell walls
mix sample with detergent - breaks down the cell membrane releasing the contents into the solution.
Add salt - breaks the hydrogen bonds between the DNA and water molecules
Add protease enzyme - this will break down the proteins associated with the DNA in the nuclei.
Add a layer of alcohol - preciptates the DNA.
The DNA will be seen as white strands forming between the layer of sample and layer of alcohol. You can pick up the DNA with a glass rod.
DNA replication
When a cell prepares to divide the two strands of DNA double helix separate and each strand serves as a template for the creation of a new double stranded DNA molecule. The complementary base pairing rules ensure that the new strands are identical to the original.
Semi Conservative replication
For DNA to replicat, the double helix structure has to unwind and then separate into two strands, so the hydrogen bonds holding the complementary bases together must be broken. The free nucleotides will then pair with their complementary bases, which have been exposed as their strands separate. Hydrogen bonds are formed between them. Finally the new nucleotides join their adjacent nucleotides with phosphodiester bonds.
Two new DNA molecules are produced with each one containing one old strand and one new strand. This is semi conservative replication
Roles of enzymes in replication
The unwinding and separation of the two DNA strands of the DNA double helix is carried out by DNA helicase. It travels along the DNA backbone catalysing reactions that break hydrogen bonds. This is known as strand unzipping.
Free nucleotides binding with the bases on the DNA. DNA polymerase catalyses the formation of phosphodiester bonds between these nucleotides.
Continuous and discontinuous replication
The strand that is unzipped from the 3’ endd can be continuously replicated as the strands unzip, and this is called the leading strand and it undergos continuous replication.
The other strand is unzipped from the 5’ end , so DNA polymerase has to wait until a section of the strand has unzipped and then work back along the strand. This results in okazaki fragments being formed. This is the lagging strand and is discontinuos replication.
