DNA
DNA is often called the blueprint of life.
In simple terms, DNA contains the instructions for making proteins
within the cell.
We study DNA for many reasons: its importance to all life on Earth, it
makes up every living organism, and it enables us to better
engineer crops.
Our genes are on our chromosomes. Every human somatic cell
should have 46 chromosomes.
The shape of DNA is called a double helix because it is like a twisted
ladder. The scientists, Watson and Crick are credited with the
discovery that DNA has this structure. All DNA molecules are
composed of nucleotides.
The backbone of the molecule is made of alternating sugars and
phosphates, while the steps of the ladder are made of
nitrogenous base pairs.
DNA has four different bases: Adenine, Thymine, Cytosine, and
Guanine.
Thymine and Cytosine are called pyrimidines, which have single
rings. Adenine and Guanine are called purines, which are double
ring bases.
These bases attract to each other because of hydrogen bonding.
These bonds are weak, but there are millions of them in a single
molecule of DNA. When making hydrogen bonds, Adenine always
pairs with thymine and cytosine always pairs with guanine.
Chargaff’s Rule states that the amounts of Adenine and Thymine are
equal and the amounts of Cytosine and Guanine are equal in a
given molecule of DNA because of the pairing between them.
Each cell has about 2 meters length of DNA. The average human
has 30 trillion cells. Therefore, the average human has enough
DNA to go from the earth to the sun more than 400 times.
RNA
RNA stands for ribonucleic acid. RNA is made from DNA, and is
single-stranded instead of double-stranded.
RNA has four nitrogenous bases as well, but one is different.
 Adenine, Cytosine, Guanine, and Uracil
There are three types of RNA: mRNA (messenger RNA), rRNA
(ribosomal RNA), and tRNA (transfer RNA)
PROTEIN SYNTHESIS
DNA begins the process called Protein Synthesis, which is also
known as the Central Dogma of biology.
This process has three steps:
 DNA Replication
 Transcription
 Translation
REPLICATION
DNA is constantly replicating in the nucleus of the cell. This has to
happen in order for protein synthesis to begin. DNA replicates
with the help of an enzyme called DNA Polymerase. Proteins are
assembled at the ribosomes, which are found in the cytoplasm.
DNA cannot leave the nucleus, so step 2—Transcription has to
occur.
DNA goes through transcription in order to make mRNA. mRNA can
leave the nucleus and goes out to the ribosomes.
Translation is the final part of the process. After rRNA has read the
message from mRNA, tRNA pairs the correct amino acid with
each section of three bases on the mRNA strand. These sections
of three are called codons.
The tRNA will keep pairing amino acids until it reaches a stop codon,
which says that the protein is finished.
Think of protein synthesis as the workings of a factory: the nucleus
would be the boss’s office, and the DNA would be the boss
himself. The boss (DNA) gives instructions for making the
product to a messenger (mRNA) and that messenger takes the
instructions to the floor. The workers read the instructions and
begin to assemble (tRNA) the product (protein).