DNA and Protein Synthesis

Why are you, YOU?• You are made of

basically four types of molecules.

• DNA is the molecule that gives instructions to your cells.

• 99.9% of human DNA is identical.

• Thus, only .1% makes you, YOU!

Where is my DNA?

DNA is bundled into structures called chromosomes.

• If the DNA in a person was stretched out it would reach to the sun and back 600 times. It is an extremely long molecule that coils really tight.

What is DNA?

• DNA is the genetic information that determines an organism’s traits.– DNA produces proteins

• DNA contains the “information for life”– Complete instructions for manufacturing all

the proteins for an organism

DNA Structure• Very long molecule!!!

• DNA is a polymer made of repeating subunits called nucleotides– Nucleotides have 3 parts:

1. Simple sugar = deoxyribose

2. Phosphate group = 1 atom of phosphorus + 4 oxygen atoms

3. Nitrogen base = carbon ring structure that contains one or more atoms of nitrogen

Nitrogen Bases• Adenine (A)

• Guanine (G)

• Cytosine (C)

• Thymine (T)

•In DNA there are four possible nucleotides, each containing one of these four bases.

Purines and Pyrimidines

How do the nitrogen bases bind?

DNA Bonding Order• Phosphate group of one nucleotide bonds

to the deoxyribose sugar of an adjacent nucleotide– Form the backbone of the chain

• Nitrogen bases bond in complementary base pairs :– Adenine (A) bonds with Thymine (T)– Guanine (G) bonds with Cytosine (C)

DNA Structure

Double Helix• In 1953, James Watson and Francis

Crick proposed that DNA is made of two chains of nucleotides joined together by the nitrogen bases.– Nitrogen bases are held together by weak

hydrogen bonds

• Shaped like a long zipper that is twisted = Double Helix

Francis CrickJames Watson

Nobel Prize, 1962

1953

Double Helix

• Rosalind Franklin and Maurice Wilkins worked together performing X-ray diffractions of the DNA model– Photographs revealed that DNA was a

tightly coiled helix

• Chargaff discovered that #A = #T & #C=#G

DNA Structure

DNA Replication

• DNA replication produces two molecules from one

• Each strand serves as a pattern to make a new DNA molecule.

• Begins as an enzyme breaks the hydrogen bonds between the nitrogen bases.– Unzips the strand

DNA Replication

• When the DNA needs to be copied so that the cell can divide the double helix starts to unwind and unzip down the hydrogen bonds.

Replication Continued• Nucleotides that are floating free in the

surrounding medium bond to the single stands by base pairing.

• Another enzyme bonds these new nucleotides into a chain.

• Each new strand formed is a complement of one of the original

• DNA Replication Animation

We will now CREATE a model of

DNA!

Proteins and Enzymes• DNA produces proteins• Proteins form key cell structures and

regulate cell functions• Enzymes are proteins that control chemical

reactions– Examples:

• Breaking down glucose molecules in cellular respiration

• Digesting food• Making spindle fibers during mitosis

Central Dogma of BiologyDNA → RNA → Protein

Transcription• DNA → RNA

• mRNA, rRNA, tRNA

• Purpose: to send instructions from nucleus to cytoplasm

Translation• RNA → Protein• @ Ribosome• Purpose: Proteins follow the instructions

and do all the jobs of the cells / organisms.• Proteins:

– 20 Amino Acids– Coded by 3 Nucleotides in RNA, called codons

Central Dogma

RNA • RNA is a single strand

• The simple sugar in RNA is ribose

• Nitrogen bases in RNA:– Adenine

– Guanine

– Cytosine

– Uracil (bonds with adenine)

3 Differences between DNA & RNA

DNA RNA

Double helix Single strand

Thymine base Uracil base

Deoxyribose sugar

Ribose sugar

Types of RNA• Messenger RNA (mRNA) = brings information

from the DNA in the nucleus to the cell’s cytoplasm

• Ribosomal RNA (rRNA) = ribosomes that clamp onto the mRNA and use its information to assemble the amino acids in the correct order.

• Transfer RNA (tRNA) = transports amino acids to the ribosome to be assembled into a protein.

Transcription• Similar to DNA replication, but the result is

the formation of one single-stranded RNA molecule (mRNA)

• Process– Enzyme unzips the DNA molecule– Free RNA nucleotides pair with complementary

DNA nucleotides– When pairing is complete, mRNA molecule

breaks away and the DNA rejoins the original strand

Genetic Code

• Three nucleotides codes for one amino acid

• Each set of nitrogen bases in mRNA represent and amino acid = CODON

• The order of the nitrogen bases in mRNA will determine the order of amino acids in a protein

• 64 combinations are possible (43)

• Some codons do not code for amino acids; they provide instructions for assembling proteins– Example: Start and Stop signals

Genetic Code Continued• UAA, UGA, UAG = stop codons

– Protein production ends at this point

• AUG = start codon + amino acid methionine

• More than one codon can code for the same amino acid

• Genetic code is universal– Cell Activities

Translation• Converts mRNA into the amino acids

that make up proteins

• Translation takes place at the ribosomes in the cytoplasm

• tRNA molecule attaches to only one type of amino acid of mRNA

• tRNA makes an anticodon of mRNA

Translation Process• tRNA brings the first amino acid to the mRNA

strand attached to the ribosome• Anticodon forms a temporary bond with the

codon of mRNA• Ribosome slides down the mRNA chain to the

next codon, and tRNA brings another amino acid

• First amino acid detaches from the mRNA in the ribosome

• Process continues until a stop codon is reached

• Most of DNA is made up of segments that are NOT expressed

• Introns are segments of genes that are not expressed (aka DNA Junk)

• Exons are segments of genes that are expressed • When RNA is made, introns and exons are

copied, then the introns are removed from the RNA while it is still in the nucleus

• Role of introns in evolution?– Very small changes in gene expression could have

dramatic effects in gene expression

Introns vs. Exons

Genetic Mutations-Latin meaning “to change”

Genetic Mutations• Any change in the DNA sequence is called a

mutation.– Mutations can effect reproductive cells– Mutations can effect somatic (body) cells

• Example = CANCER

• Types of Mutations:– Point mutation– Frameshift mutation

• Insertions or Deletions

– Chromosomal mutation

Point Mutation• A change in a single base pair in DNA• Example 1:

– THE DOG BIT THE CAT.

– THE DOG BIT THE CAR.

• Example 2:– THE DOG BIT THE CAT.

– THE DOG HIT THE CAT.

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

Frameshift Mutation• A single base pair in DNA is deleted or

inserted.• Every codon after the deleted base would

be different.• Entire codons can be inserted or deleted• Example:

– THE DOG BIT THE CAT.– THE DOB ITT HEC AT.

Chromosomal Mutations• Five kinds of chromosomal mutations:

– Deletions occur when part of a chromosome is left out.

– Insertions occur when a part of a chromatid breaks off and attaches to its sister chromatid.

– Inversion occur when part of a chromosome breaks off and is reinserted backwards.

– Translocation occur when part of one chromosome breaks off and is added to a different chromosome.

– Nondisjunction – failure of homologous chromosomes to separate during meiosis

Mutations

Deletion

Duplication

Inversion

Translocation

Causes of Mutations• Spontaneous:

– Mistake in base pairing during DNA replication or protein synthesis– Errors in cell division

• Mutagen – agent that causes DNA change– High energy radiation

• X-rays, UV light

– Chemicals• Dioxins, asbestos, benzene, cyanide, formaldehyde

– High temperatures

Mutagen Video

What is a karyotype?

• Errors from nondisjunction can be determined by performing a karyotype

• Make a karyotype…

• Cells collected from unborn child through amniocentesis (skin cells obtained)

• Blood sample taken from individual

Sample Karyotypes#1 #2

Sample Karyotypes#3

Sample Karyotypes#4