Chapter 6Transcription and Trasnlstion

DNA is in the Nucleus

• DNA is deoxyribonucleic acid

• It is double stranded and carries all genetic material in living organisms

• DNA contains genetic information in pieces called chromosomes• Chromosomes are threadlike structure of DNA

• Humans have 23 pairs of chromosomes, or 46 total

• Different species have different numbers of chromosomes, for example dogs have 78, mosquitos have 6, and field horse tail (a plant) has 216!

Why does DNA replicate itself?

• To grow, to reproduce to make new cells

How does DNA replicate?

1. The double helix unwinds

2. DNA polymerase (an enzyme) attaches to each strand

3. Enzymes line up nucleotides according to rules (GCAT)

4. Hydrogen bonds form between the new base pairs (making the "rungs" of the DNA ladder)

4. Bonds form between the sugar phosphate components (to form the sides of the DNA ladder)

5. The new DNA twists up into the helix we all know and love

How does DNA replicate?

Cool bits to know...

• The original strand of DNA is the parent strand

• The new strands are the daughter strands

• Replication begins at the origins of replication

• Each DNA strand acts as a template for a new complementary strand

Where did your chromosomes come from?

• Chromosomes are found in pairs, homologous pairs• homologous means: having the same relation, relative position, or structure,

in particular.

• You get one chromosome from each parent, your mom gave you 23 chromosomes and your dad gave you 23 chromosomes

• Check out the cool picture on the next slide!

We are diploid

• Humans are diploid, meaning we have 2 of each chromosome

• Another way to say diploid is to say 2n

• Other organism may not be diploid, for example Durum wheat or macaroni wheat is tetraploid or 4n

This is a mouse karyotype of a cell with cancer, that is why some chromosomes are tetraploid

What do chromosomes (and DNA) do?

• DNA’s job is to carry out the instructions for making proteins

• DNA is long, and carries a lot of information

• In DNA, there are portions that code for proteins, these are called genes

• The other portions are considered non-coding DNA

• Scientists used to believe that non-coding DNA was junk, and called it junk DNA

• Now they believe that non-coding regions may be involved in gene relgulation

What do chromosomes (and DNA) do?

• This image shows a cell with the chromosomes in the nucleus, and zooms all the way into the base pairs

CENTRAL DOGMA OF MOLECULAR BIOLOGY

Wait, what is dogma?

• An awesome movie with Ben Affleck

• And, a principle or set of principles laid down by an authority as incontrovertibly true (thank you Google!)

CENTRAL DOGMA OF MOLECULAR BIOLOGYNow back to the…

Remember our old friend RNA?

• RNA is similar to DNA…BUT…• It is single stranded

• It has a U instead off a T (GCAU vs GCAT)

• The sugar in the sugar phosphate backbone is a ribose

CENTRAL DOGMA OF MOLECULAR BIOLOGYLook at RNA, right in the center there of the…

And Proteins

• Proteins are macromolecules, consisting of long chains of amino acids

• Amino acids have a amino end and a carboxyl end

• Amino End Carboxyl End

CENTRAL DOGMA OF MOLECULAR BIOLOGYLook at those proteins being created, at the end of the…

Where does RNA come from?

• The process of transcription leads to the creation of RNA

• RNA transcription is similar to DNA replication

1. The double helix of DNA unwinds

2. RNA polymerase (an enzyme) attaches to one strand

3. Enzymes line up nucleotides according to rules (GCAU)

4. RNA is released (Since RNA is one stranded, that’s it!)

5. DNA strand rejoins it’s complimentary strand

• Only the genes that are needed are transcribed, not the entire DNA strand

Where does RNA come from?

Types of RNA

• mRNA – messenger RNA, carries information from DNA to ribosome for protein synthesis

• rRNA – ribosomal RNA, interacts with cells ribosome to make them functional

• tRNA – transfer RNA, carries amino acids from cytoplasm to ribosome during protein synthesis

How do we get from RNA to Protein?

• RNA gets translated from the language of nucleotides to the language of amino acids in a process called translation

• Nucleotides are read on the mRNA in sets of three, called codons

A little more about Amino Acids and Codons…

• There are 20 different amino acids

• Amino acids are typically referred to by a three letter code

• Methionine (met), is the amino acid that is made with translation begins

• The start codon is AUG, there is only one

• There are three stop codons, UAA, UGA, and UAG

An Example:

tRNA, Bringing the Amino Acids to the Ribosome

• Here is an image of a tRNA molecule

• Note the following locations• Amino acid attachment site

• Where the amino acids attach

• Anticodon loop• Where the tRNA attaches to the mRNA

• Attachment sites, amino acid and anticodon loop

Other looks for tRNA

Anticodon Loop

• Anticodon loop is the loop at the bottom of the tRNA molecule, it is a set of three nucleotides that decode the order of amino acids needed to create the amino acid chain or protein

The Ribosome, the party happens here

• The ribosome is where the action of translation happens!

• The ribosome is the organelle that synthesizes protein

• There are 2 binding sites on the ribosome, the A site and the P site (there is also the E site, but binding does not occur there)

Other images of ribosomes

How this works…

• First, the tRNA comes in and binds at the A-site

• The tRNA knows where to bond based on the codon of the mRNA

• The A-site is where the peptide bond occurs between the amino acid on the new tRNA and the tRNA at the P-site

• Once the bond is formed, the tRNA at the P-site releases its amino acid and returns back to the cytoplasm

• The tRNA that was at the A-site then moves to the P-site and a new tRNA moves into the A-site

A few more bits to know

• Translation stops when a stop codon is appears

• Stop codons are UAG, UGA, or UAA

• In the ribosome the A is A-site stands for amino acid, and the P in P-site stands for peptide

Putting it all together….