DNA, RNA, and Protein Synthesis Chapter 10. Discovery of DNA 1928- Fredrick Griffith –He found that when harmless bacteria are mixed with dead harmful.

DNA, RNA, and Protein Synthesis

Chapter 10

Discovery of DNA

• 1928- Fredrick Griffith – He found that when harmless

bacteria are mixed with dead harmful bacteria, the harmless will absorb the genetic material of the harmful and become harmful themselves

– Transfer of genetic material is called transformation

Discovery of DNA• 1940s- Avery and colleagues

– Wanted to know what caused transformation (DNA, RNA, or protein)

– They separated these individual parts and tested them.

– They found DNA was the cause of transformation

– In other words, they found if harmless bacteria took in harmful bacteria’s DNA, the harmless became harmful.

Discovery of DNA• 1952- Hershey and Chase

– Wanted to test whether DNA or protein was the genetic material that viruses pass on when they infect an organism.

– They used viruses that infect bacteria (called bacteriophages)

– They radioactively labeled the DNA and the protein (this allowed them to trace the path of each)

– They found DNA was injected into the bacteria to infect it, not protein. So DNA was the genetic material

Discovery of DNA

• 1950s- Watson, Crick, Franklin, and Wilkins

– Franklin and Wilkins discover DNA is helical

– Watson and Crick build a model of DNA and determine it is a double helix

DNA Structure

• Made of nucleotides

(so nucleotides are the monomers of DNA!)

–Nucleotides have 3 parts:

1.Nitrogenous base (there are 4 kinds)

2.Phosphate Group

3.5 carbon sugar called deoxyribose

phosphate

deoxyribose

bases

nucleotide

DNA Structure

• Nitrogenous bases:– Contain nitrogen and is

a base– Purines- (double ringed)

• Adenine (A)• Guanine (G)

– Pyrimidine's- (single ringed)• Cytosine (C)• Thymine (T)

DNA Structure

• DNA is made up of 2 straight chains of nucleotides

• The bases on each of those chains are attracted to each other and form hydrogen bonds

• The force of thousands or millions of hydrogen bonds keeps the two strands of DNA held tightly together

DNA models

• Since the sugar-phosphate “backbone” of DNA never change, we often simplify DNA into the letters of the nitrogenous bases.

• For example, this DNA strand can be simplified to…

TGACACTG

DNA Structure

• Base pairing rules in DNA:– Hydrogen bonds form between specific pairs– Adenine ALWAYS pairs with Thymine – Cytosine ALWAYS pairs with Guanine– These pairs (A-T and C-G) are called

complementary base pairs– Each complimentary pair contains one single

and one double ringed base

DNA Structure

• Because of the base pairing rules, one strand of DNA is complementary to the other strand (otherwise they would not stick together!)– The order of the nitrogenous bases on DNA is

called its base sequence– So if one strand has a base sequence of

TGCC, the other strand will have ACGG.

Let’s Practice

• Write the complimentary strand for…

TGACCGAT

TGGCCAATATA

END DAY 1

DNA Replication• DNA Replication is the process by which DNA is

copied in a cell before the cell divides.

DNA Replication• Step 1:

Enzymes called Helicases separate the two strands of DNA

• Hydrogen bonds are broken• Replication fork: Y-shaped region formed as bonds are broken

DNA Replication

• Step 2:

Enzymes called DNA polymerases add

nucleotides to the separated strands • Nucleotides are found floating free in the nucleus

• The addition of new nucleotides occurs in opposite directions

addition towards the replication fork

addition away from the replication fork

DNA Replication• In Eukaryotes, several replication forks form and

replication continues until all of the DNA has been replicated. – If only 1 was formed it would take too long to replicate DNA (53 days for

humans!!)

• Once replication is complete, 2 DNA molecules exist. – Each molecule is made from one old strand and one new

• This is called semi-conservative replication since each new strand has kept one of the original strands.

DNA Replication• Replication is usually very accurate

– There is only about 1 error for every BILLION nucleotides added!

– The reason is that DNA Polymerases also “proof-reads” the DNA and fixes any errors during replication

DNA Replication

• If an error does occur, it results in a different nucleotide sequence in the new DNA strands called a mutation– A change in even one nucleotide can be very

harmful to an organism

– Some mutations can affect the growth of cells, causing growth to accelerate, resulting in cancer

– Changes can be good - mutations sometimes lead to adaptations and therefore evolution

Protein Synthesis

• DNA is the “code” for hereditary characteristics.

• The genetic code is how organisms store hereditary information which is first translated into amino acids

• DNA codes for all of the body’s proteins (like enzymes)

Protein Synthesis

–Genes are sequences located in DNA that code for specific characteristics

– The code (or gene) for the production of the protein melanin is in your DNA and creates your hair and skin color

Protein Synthesis

• The “code” or “recipe” within DNA cannot be read directly-

– DNA cannot leave the nucleus and proteins are made in the cytoplasm of cells

– So the code is transcribed (copied) and translated (turned into something useful) by ribonucleic acid (RNA)

However,

Protein Synthesis

• Remember, proteins make us who we are– Responsible for

• chemical reactions • hereditary characteristics (such as eye color)

– Recall the monomers of proteins are amino acids

– DNA holds the recipe for the amino acid sequence of all the proteins we make

DNA vs RNA

• Both are made of nucleotides• Both are involved in protein synthesis• DNA has the sugar deoxyribose, while

RNA has the sugar ribose• RNA uses the nitrogenous base uracil (U)

instead of thymine (T) used in DNA• RNA is single stranded, while DNA is

double stranded• RNA is usually MUCH shorter than DNA

END DAY 2

Protein Synthesis

• There are three major types of RNA– Messenger RNA (mRNA) – carries the genetic

instructions from the DNA to the ribosomes

– Ribosomal RNA (rRNA) – part of the structure of ribosome• Remember ribosomes make proteins

Protein Synthesis

Protein Synthesis

– Transfer RNA (tRNA)

– transfers the amino acids to the ribosomes to make proteins

Protein Synthesis Transcription

• The first step in protein synthesis is transcription:– RNA polymerase (enzyme)

binds to a genes promoter region• A promoter is just a

specific nucleotide sequence where the RNA polymerase can attach

– The RNA attaches to the RNA polymerase and the DNA begins to uncoil

Transcription cont.

• The RNA polymerase adds complimentary nucleotides resulting in a straight chain RNA molecule– The DNA code

determines what bases will be added

– Example if the DNA code for a gene is ATCCGTT, then the RNA will be UAGGCAA

– Remember, RNA does not have Thymine, it has Uracil!!

• The copying of DNA continues until the RNA polymerase reaches a termination signal– That is a specific sequence

of nucleotides that tells the RNA polymerase to “STOP” and release the RNA and DNA

– The RNA is called mRNA, because it is the messenger of the “code” from the DNA to the ribosomes

Transcription cont.

END DAY 3

• Once the newly made RNA leaves the nucleus it attaches to a ribosome at the promoter region.

• Ribosomes will “read” 3 nucleotides in the RNA code at a time– These 3 nucleotides are

called codons.– Each Codon codes for

• START signal• Amino Acid• STOP signal

Protein Synthesis - Translation

• Example, the sequence AUG codes for the amino acid Methionine a START signal (This is the only start signal)

– ALL mRNA molecules start with AUG, otherwise, they would not have a start region for protein synthesis

Translation cont.

• So, in translation, the RNA is translated into amino acids, which are put together to form proteins (or polypeptides)

• The translation occurs with the help of tRNA, which carries the amino acids

Translation cont.

• When the ribosome reads the start sequence (AUG), a tRNA molecule comes along with the anticodon

– The anticodon is the complementary sequence.

– The complementary bases bond with each other and the amino acid methionine begins the protein synthesis within the ribosome

– So, tRNA transfers amino acids to the ribosome

Translation cont.

• Recall there are only 20 amino acids

• Most amino acids have more than one codon– Example, Leucine’s

codons are UUA, UUG, CUU, CUC, CUA, and CUG

• But each codon codes for ONLY 1 amino acid– Example, CUU only

codes for Leucine and nothing else

Amino Acids

• After the start sequence, the ribosome moves to the next codon.– Let’s say the next

codon is GUC– Now a tRNA that has

the anticodon for that codon attaches to the ribosome carrying the amino acid Valine.

– The amino acid Valine attaches to the Methionine from before (now we have a dipeptide!)

Translation cont.

• This process continues and the polypeptide grows until the STOP codon is reached

– UAA, UAG, and UGA are the only stop codons

– The protein, ribosome and all RNA is released to perform other needed functions

Translation cont.

Protein Synthesis - Overview• Amino Acids are listed by their CODON!!!

– That would be the 3 nucleotide sequence on the mRNA

Protein Synthesis - Overview

• Now use the CODON chart to figure out the amino acid sequence

Protein Synthesis - Overview•1 – Methionine (start)•2 - Threonine•3 – Glutamic acid•4 - Leucine•5 - Arginine•6 - Serine•7 - STOP

Some Great Resources

• http://nobelprize.org/educational_games/medicine/dna_double_helix/index.html– DNA games