QOD 1/3/12

• What is the shape of DNA?

DNA, RNA, and Protein Synthesis

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

•DNA is a double helix

DNA Structure

• It is 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)

– Pyrimadines- (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 Structure• If DNA was a spiral

staircase…– The alternating sugar

and phosphates would be the hand rails.

– The bases would be the steps

– But, they would be weak steps as they are only held together by hydrogen bonds

DNA models

• Since the sugar-phosphate “hand rails” 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!)– So if one strand has a base sequence of

TGCC, the other strand will have ACGG.

Let’s Practice

• Right the complimentary DNA strand for…

TGACCGAT

ACTGGCTA

QOD 1/4/12

• Which scientists built the first model of DNA?

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

copied in a cell before the cell divides.

DNA Replication

• First, enzymes called Helicases separate the two strands of DNA– Helicases break hydrogen

bonds

DNA Replication• Next, enzymes called DNA

polymerases add complimentary nucleotides to the separated strands of DNA– Nucleotides are found

floating freely in the nucleus

DNA Replication• When replication is

finished, there are 2 DNA molecules, each had one old strand and one new strand

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 “proofread” the DNA and fix any errors during replication

DNA Replication

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

harmful to an organism (for reasons we will see later)

– Some mutations can affect the growth of cells, causing growth to accelerate, this results 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 and translate it into proteins

Protein Synthesis

• DNA codes for all of the bodies proteins (like enzymes)– Genes are sequences located in the 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

– The code or recipe for all of the enzymes that help you digest your food is located in your DNA

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)

Protein Synthesis

• Remember, proteins make us who we are– They are responsible for chemical reactions

occurring in us (enzymes) and for the hereditary characteristics that we have (such as eye color)

– The building blocks (or monomers) of proteins are amino acids

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

Protein Synthesis

• RNA directs protein synthesis, which is the making of proteins from DNA

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

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

double stranded• RNA is usually MUCH shorter than DNA

Protein Synthesis

• There are several types of RNA involved in protein synthesis– Messenger RNA (mRNA)

– carries the genetic instructions from the DNA to the ribosomes

Protein Synthesis– Ribosomal RNA (rRNA) – part of the

ribosome• Remember ribosomes make proteins

Protein Synthesis

– Transfer RNA (tRNA) – transfers the amino acids to the ribosomes to make proteins

QOD 1/6/12

• What type of RNA carries the genetic instructions from the DNA to the ribosomes?

Protein Synthesis - Transcription

• The first step in protein synthesis is transcription:– An Enzyme called RNA

polymerase 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

Protein Synthesis - Transcription

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

determines what bases will be added (A with U, T with A, and G with C)

– For 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 STOP signal– That is a specific sequence

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

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

Protein Synthesis - Transcription

Let’s Practice

• What is the mRNA strand for the following DNA sequences??

– DNA - ATCGGT– mRNA - UAGCCA

Let’s Practice

• What is the DNA sequence that the following mRNA strands came from??

– mRNA - GUCAUG– DNA - CAGTAC

• 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

an amino acid, a START signal, or a STOP signal

Protein Synthesis - Translation

• For example, the sequence AUG codes for the amino acid Methionine and means START(it is the only one that means start)– ALL mRNA molecules

start with AUG, otherwise, they would have a start region for protein synthesis

Protein Synthesis - Translation

• 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

Protein Synthesis - Translation

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

complementary sequence, which would be UAC.

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

– tRNA transfers amino acids to the ribosome

Protein Synthesis - Translation

• There are only 20 amino acids

• Most amino acids have more than on codon– For example, Leucine’s

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

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

codes for Leucine and nothing else

Protein Synthesis - Translation

• 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 CAG would attach to the ribosome and it would carry the amino acid Valine.

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

Protein Synthesis - Translation

• 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

Protein Synthesis - Translation

Protein Synthesis - Summary• Let’s learn how to BREAK THE CODE!!

Protein Synthesis - Summary•This is an mRNA strand- figure out what the DNA code was that it came from:

Protein Synthesis - Summary•1 - TAC•2 - TGC•3 - CTC•4 - GAA•5 - GCC•6 - TCG•7 - ATC

Protein Synthesis - Summary•Now figure out the anticodons (which will be found on the tRNA)

Protein Synthesis - Summary•1 - UAC•2 - UGC•3 - CUC•4 - GAA•5 - GCC•6 - UCG•7 - AUC

Protein Synthesis - Summary

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

Protein Synthesis - Summary

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

QOD 1/11/12

• What is the amino acid for AUG?

Genetic Mutations• Can effect reproductive and body cells.

– Reproductive cells: Offspring may have genetic disease.

– Body cells: Can cause cancer or may have no effect.

• Can change the entire structure of a protein, and effect the shape of the protein.

• MYTH: All mutations are bad.

Point mutations • Occurs when a single base changes. Types:– Silent mutation- no

amino acid change

– Missense- changes amino acid that is coded.

– Nonsense- changes sequence to a stop codon.

• Frameshift is a shift in the reading frame of DNA sequence

• changes everything “downstream” (after)

• Types:– Insertions- adding

base(s)

– Deletions- losing base(s)

Frameshift mutations