Transcription and translation

The DNA is divided into genes, which contain instruction for making proteins that make up a human. Thus, the instructions from genes in the DNA are used to make proteins. This process is called the central dogma, and it is divided into transcription and translation (described below:))

TRANSCRIPTION: Transcription occurs in the nucleus. The DNA is like a cookbook full of different recipes (genes/segments of DNA) that contain instructions about how to make proteins. Thus, if we want to make a protein, we need to copy the recipe (information in a gene) in the DNA. This is what transcription is all about.

An enzyme called RNA polymerase moves down the DNA and copies the information in it. The transcript of this information is called the messenger RNA (mRNA). However, we need to alter it a little bit before it can leave the nucleus. We need to add 5′ cap and poly(A) tail, and we must get rid of parts that don’t code for a specific amino acid.

TRANSLATION: Translation occurs in the cytoplasm. When the mRNA leaves the nucleus, it enters a ribosome. The ribosomes are protein factories. The mRNA moves through the ribosome. The amino acids that are needed to make the protein are brought by transfer RNA (tRNA). There are many types of tRNA, and each type attaches to a specific amino acid.

The tRNA attaches to the codon (three nucleotides that code for specific aminoacids) on the mRNA, and leaves the amino acid (see the picture below). This way, amino acids are bonded together, forming a polypeptide chain (a protein). This protein is later used in our body.

PLEASE CHECK OUT MY VIDEO ABOUT THE CENTRAL DOGMA HERE :)

The structure of proteins

Amino acids

Proteins are made of amino acids, which are bonded together by bonds called peptide bonds. The picture below depicts an amino acid.

As you can see, an amino acid consists of an amino group (NH2), a carboxyl group (COOH) and a variable, which is also called R. The variable is different in every amino acid, and this is why each of them is unique. 

The structure of proteins

The shape (conformation) of a protein determines what job it preforms. There are four levels of protein structure, all of them discussed and pictured below :).

PRIMARY STRUCTURE: The primary structure refers to the sequence of aminoacids in the protein. The amino acids are bond together by peptide bonds and thus form a long chain called a polypeptide chain. This chain of amino acids is an example of primary structure of a protein.

SECONDARY STRUCTURE: The secondary structure refers to a protein chain that is coiled up, either as alpha helix or beta pleated sheet (pictured below). The chain coils up because of the hydrogen bonds between the amino acids.

TERTIARY STRUCTURE: The tertiary structure is the three-dimensional (not just flat) conformation (shape) of a protein. It determines the specifity of the protein, and some factors that contribute to the tertiary structure are for example hydrogen bonds between R-groups, Ionic bonds between R-groups or disulfide bonds between cysteine amino acids.

QUATERNARY STRUCTURE: The quaternary structure refers to proteins made up of more than one polypeptide chains. An example of that is hemoglobin, which is essential in order to carry oxygen in our blood. 

PLEASE, CHECK OUT MY VIDEO ABOUT PROTEIN STRUCTURE :) 

Hydrogen bonds

The structure of a water molecule

To better understand the hydrogen bonds, let's first look at a model of a water molecule (pictured below).

 The water molecule is made of two hydrogen atoms and one oxygen atom. They are sharing the electrons. However, since the oxygen atom has a greater mass than the hydrogen atom, it exerts a stronger pull on the electrons than the hydrogen does, so the electrons spend most of their ''time'' closer to the oxygen. As a result of that, oxygen becomes negatively charged, and hydrogen becomes positively charged. Since the water molecule has two opposite poles , it's called a polar molecule or a dipole.

Hydrogen bonds

Now, when we have many (DIPOLE!) water molecules next to each other, the (positively charged) hydrogen atoms from one water molecule are attracted by the (negaltively charged) oxygen molecules. In other words: there is a force of attraction between them.
THE FORCE OF ATTRACTION BETWEEN A POSITIVELY CHARGED HYDROGEN ATOM AND NEGATIVELY CHARGED OXYGEN ATOM (FROM ANOTHER MOLECULE!)IS AN EXAMPLE ON A HYDROGEN BOND. Please look at the image below to get a better understand how hydrogen bonds look like/work (the green lines/dots = hydrogen bonds :))

The hydrogen bond is called the hydrogen bond because it refers to the force of attraction of a hydrogen atom (which is positively charged because it is a part of a polar/dipole molecule, such as water). However, the negatively charged atom doesn't have to be an oxygen atom. Hydrogen bonds can also be formed between a hydrogen and fluorine or nitrogen.

Why did I include the post about hydrogen bonds in this blog(which is supposed to be about biology:))?

It seems like it doesn't make sense to learn chemistry when our main interest is biology, but the truth is that we must know some chemistry if we want to understand biology.
The next post that I plan to make is going to be about proteins. Understanding hydrogen bonds is crucial if we want to understand the structure of proteins.