DNA mRNA
Protein

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Every living thing is made up of cells.
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There are differences between different types of cells, but they’re made of the same building blocks which are called genes.

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Everything has genes.
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They cluster together to form chromosome.
a
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Chromosomes are made up of thousands of genes, which in turn are made up of DNA.

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Your body’s chromosomes contain about 30,000 genes.
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The DNA in your genes gives instructions that makes you who you are.
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For example, different genes in your body determine your eye colour and your height.

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Nucleic acids include two related molecules, deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA).

DNA and RNA are polymers of subunits called nucleotides , and the order of these nucleotides determines the information content.
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Nucleotides have three components: a phosphate group , a five-carbon sugar, and a nitrogen-containing base .

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Each phosphate connects two sugars via a phosphodiester bond.
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This connects the nucleotides into a chain that runs in a 5′ to 3′ direction.
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The 5′-OH of the sugar of one nucleotide is linked via oxygen to the phosphate group.
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The 3′-OH of the sugar of the following nucleotide is linked to the other side of the phosphate.

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The five-carbon sugar or pentose is different for DNA and RNA.
DNA has deoxyribose , whereas RNA uses ribose . These two sugars differ by one hydroxyl group.
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There are 4 potential bases that can be attached to the sugar In DNA, guanine, cytosine, adenine, or thymine

In RNA, thymine is replaced with uracil.

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The most stable structure occurs when another single strand of nucleotides aligns with the first to form a double-stranded molecule, as seen in the
DNA double helix .

Each base forms hydrogen bonds to a base in the other strand. The two strands are antiparallel
, that is, they run in opposite directions with the
5′end of the first strand opposite the 3′end of its partner and vice versa.


The bases are of two types, purines ( guanine and adenine) and pyrimidines (cytosine and thymine). Each base pair consists of one purine connected to a pyrimidine via hydrogen bonds.

Guanine pairs only with cytosine (G-C) via three hydrogen bonds. Adenine pairs only with thymine (A-T) in DNA or uracil (A-
U) in RNA via two hydrogen bonds.


Bacteria have just a few thousand genes, each approximately 1000 nucleotides long. These are carried on a chromosome that is a single giant circular molecule of DNA.

A single DNA double helix with this many genes is about 1000 times too long to fit inside a bacterial cell without being condensed somehow in order to take up less space.
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In bacteria, the double helix undergoes supercoiling to condense it.

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The haploid human genome contains approximately 3 billion base pairs of DNA packaged into 23 chromosomes. Of course, most cells in the body (except for female ova and male sperm) are diploid, with 23 pairs of chromosomes . That makes a total of 6 billion base pairs of DNA per cell.

Because each base pair is around 0.34 nanometers long (a nanometer is one-billionth of a meter), each diploid cell therefore contains about 2 meters of DNA [(0.34 × 10 -9 ) × (6 × 10 9 )].

Moreover, it is estimated that the human body contains about 50 trillion cells —which works out to 100 trillion meters of DNA per human.

Now, consider the fact that the Sun is 150 billion meters from Earth.
This means that each of us has enough DNA to go from here to the Sun and back more than 300 times, or around Earth's equator
2.5 million times !

How is this possible?


Supercoiling is induced by the enzyme DNA gyrase , which twists the DNA in a left-handed direction so that about 200 nucleotides are found in one supercoil.

The twisting causes the DNA to condense.
Extra supercoils are removed by

The supercoiled DNA forms loops that connect to a protein scaffold.

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In humans and plants, vastly more DNA must be packaged, so just adding supercoils is not sufficient. Eukaryotic
DNA is wound around proteins called histones first.


Histones have a positive charge to them, and this neutralizes the negatively charged phosphate backbone.

DNA plus histones looks like beads on a string and is called chromatin . Each bead or nucleosome has about 200 base pairs of
DNA and nine histones ,


The histones are highly conserved proteins that are found in all eukaryotes .

In regions of DNA that are expressed, the histones are loose , allowing regulatory proteins and enzymes access to the DNA.

In regions that are not expressed, the histones are condensed , preventing other proteins from accessing the DNA (this structure is called heterochromatin ).

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
The production (synthesis) of proteins .
3 phases:
1. Transcription
2. RNA processing
3. Translation

DNA  RNA  Protein


RNA molecules are produced by copying part of DNA into a complementary sequence of RNA

This process is started and controlled by an enzyme called RNA polymerase .

This produces pre mRNA

DNA
RNA Polymerase pre-mRNA

Splicing

Splicing is the process by which pre-mRNA is modified to remove certain stretches of non-coding sequences called
introns; the stretches that remain include protein-coding sequences and are called exons.

Splicing is usually performed by an RNA-protein complex called the spliceosome , but some RNA molecules are also capable of catalyzing their own splicing step.

pre-RNA molecule exon intron exon intron exon exon intron splicesome intron exon splicesome exon exon exon exon
Mature RNA molecule


Three types of RNA:
A. messenger RNA (mRNA)
B. transfer RNA (tRNA)
C. ribosome RNA (rRNA)

Remember: all produced in the nucleus!


Carries instructions from DNA to the rest of the ribosome.

Tells the ribosome what kind of protein to make

Acts like an email from the principal to the protein kitchen.

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Part of the structure of a ribosome
Helps in protein production is the central component of the ribosome's protein manufacturing machinery.
tRNA

Gets the right parts to make the right protein according to mRNA instructions

mRNA start codon
A U G G G C U C C A U C G G C G C A U A A codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 protein methionine glycine serine isoleucine glycine alanine stop codon aa1
Primary structure of a protein aa2 aa3 aa4 peptide bonds aa5 aa6

Large subunit
P
Site
A
Site
Small subunit

amino acid attachment site methionine amino acid
U A C anticodon


Three parts:
1.
initiation : start codon (AUG)
2.
elongation :
3.
termination : stop codon (UAG)

Let’s make a PROTEIN!!!!
.

Large subunit peptidyl-tRNA site
P
Site aminoacyl-tRNA site
A
Site
A U G mRNA
C U A C U U C G
Small subunit

aa2 aa1 anticodon hydrogen bonds
1-tRNA
U A C
A U G codon
G
2-tRNA
A U
C U A C U U C G mRNA
A

peptide bond aa1 aa2 aa3 anticodon hydrogen bonds
1-tRNA
U A C
A U G codon
3-tRNA
G A A
2-tRNA
G A U
C U A C U U C G A mRNA

aa1 aa2 peptide bond aa3
1-tRNA
U A C
(leaves)
A U G
3-tRNA
G A A
2-tRNA
G A U
C U A C U U C G A mRNA
Ribosomes move over one codon

aa1 peptide bonds aa2 aa3 aa4
A U G
4-tRNA
G C U
2-tRNA 3-tRNA
G A U G A A
C U A C U U C G A A C U mRNA

aa1 peptide bonds aa2 aa3 aa4
G
2-tRNA
A U
(leaves)
A U G
4-tRNA
G C U
3-tRNA
G A A
C U A C U U C G A A C U mRNA
Ribosomes move over one codon

aa1 aa2 peptide bonds aa3 aa4 aa5
5-tRNA
U G A
3-tRNA 4-tRNA
G A A G C
G C U A C U U C G
U
A A C U mRNA

aa1 aa2 peptide bonds aa3 aa4 aa5
3-tRNA
G A A 4-tRNA
G C U
G C U A C U U C G A A C U
5-tRNA
U G A mRNA
Ribosomes move over one codon

aa5 aa4 aa3 primary structure of a protein aa2 aa1
A C U mRNA aa199 aa200
200-tRNA
C A U G U U terminator or stop codon
U A G

aa2

The end products of protein synthesis is a primary structure of a protein .

A sequence of amino acid bonded together by peptide bonds.
aa5 aa4 aa3 aa199 aa1 aa200