Biology DNA & RNA

DNA (deoxyribonucleic acid)

The genetic blueprint for each cell that determines every characteristic of a living organism.

A DNA nucleotide is made up of three main parts:

Deoxyribose (simple sugar or pentose sugar)

Phosphate group

Nitrogen base

How to draw DNA

Nitrogen Base Pairing

Adenine bonds with Thymine

Cytosine bonds with Guanine

What do nucleotides do

They combine to form two long chains (making one molecule).

The importance of replication in DNA

DNA must replicate so that each cell has a complete set of chromosomes

Without replication: Species could not survive

Individuals could not grow, heal or reproduce

Where does replication begin

Replication begins at specific locations called origins of replication, where the DNA strands are separated to allow for copying.

Step 1 of replication:

The enzyme, helicase, untwists the double helix at the replication fork, separating the two old strands and breaking the Hydrogen bond.

What is the replication fork?

The Y-shaped region where the new strands of DNA are elongated.

Step 2 of replication

Each strand then builds its opposite  strand by pairing its bases with free nucleotides. 

What does the DNA polymerase do in the 2nd step of replication

Adds complementary nucleotides to the growing DNA strand. Responsible        for the elongation of new DNA at a  replication fork.

Step 3 of replication

Each new DNA molecule has one nucleotide strand from the original DNA molecule and one nucleotide strand that has been newly synthesized from free nucleotides in the cell.

Semi-Conservative Replication

Half old DNA , half new DNA

The replication process goes on until..

This process goes on until the entire molecule has been unzipped and replicated.

Each new strand is a complementary strand from  the original strand.

The two strands of DNA are…

anti-Parallel- which means one runs from 5’->3’ and one runs from 3’->5’.

DNA vs RNA

DNA	RNA
Double stranded Thymine Sugar= deoxyribose NEVER leaves the nucleus	Single stranded  Uracil Sugar= ribose Leaves the nucleus

What are the 3 types of RNA?

tRNA, mRNA, rRNA

mRNA (messenger RNA)

RNA copy that carries information from the DNA in the nucleus out into the cytoplasm of the cell.

rRNA (ribosomal RNA)

The RNA that makes up the ribosome.

Helps produce enzymes needed to bond amino acids together during protein production.

tRNA (transfer RNA)

Brings amino acids to the ribosomes so they can assemble into proteins.

Anticodons

Three unpaired bases on a tRNA molecule.  These bases are complementary to one mRNA codon.

Transcription

The creation of mRNA under the direction of DNA

Enzymes making an mRNA copy of a DNA strand

Takes place in the nucleus

Step 1 of transcription

An enzyme, helicase, unzips the molecules of DNA, just as it does during DNA replication.

Step 2 of transcription

Free RNA nucleotides pair with complementary DNA nucleotides on one of the DNA strands.

Assisted by RNA polymerase

RNA elongates

Step 3 of transcription

Transcription ends when the RNA polymerase molecule reaches the terminator region of the DNA

The mRNA molecules break away as the DNA strands rejoin

Translation

mRNA to protein

Where does translation occur

Ribosome

Translation is the process of…

Reading codons

Laying amino acids in chains

Making proteins

What does tRNA do in translation?

Brings amino acids to the ribosomes so they can assemble into proteins.

What is a codon

A sequence of three consecutive nucleotides in a DNA or RNA molecule that codes for a specific amino acid.

Step 1 of translation

The first codon of the mRNA strand attaches to a ribosome

The tRNA molecule (carrying a specific amino acid) approaches the ribosome

When the tRNA anticodon pairs with the mRNA codon, the two molecules join and the tRNA molecule remains there

Step 2 of translation

Can’t start unless there is a start codon (AUG) on mRNA that signals the start.  Once it starts, the ribosome slides to the next codon.

Step 3 of translation

A new tRNA molecule carrying an amino acid pairs with the mRNA codon.

Step 4 of translation

When the first and second amino acids are in place, a peptide bond is formed between them.

Step 5 of translation (last step)

As the process continues, a chain of amino acids is formed.  This occurs until the mRNA reaches a stop codon.