Understanding DNA

Presented by:

Mrs. Nelson

OVERVIEW Name the four organic compounds

found in all living things. The focus of this chapter will be: What are the elements found in nucleic

acids? What is the subunit? What are the two types of nucleic acids? What is the function of DNA?

Discovering DNA Frederick Griffith

studied bacteria cause pneumonia.

Smooth strain -disease

Rough strain - harmless

What caused the difference?

Griffith’s Experiment

Griffith’s Conclusion

The harmless bacteria could “acquire” the ability to cause disease. How?

Transformation Bacteria can take “something” from

each other By doing so, they can take on different

traits.

Transformation

Discovery of DNA

Griffith didn’t know what it was that bacteria were taking from each other.

He did know that this “something” gave organisms their traits.

Later, it was discovered that this was DNA.

DNA (Deoxyribonucleic acid). All living things contain DNA. Source of genetic traits because it is the

the directions cells use to build proteins.

Where is DNA?Cell Nucleus Chromosome Gene DNA

Chromosomes a closer look …

What does DNA look like? DNA made subunits: nucleotides Nucleotide: sugar (deoxyribose),

phosphate group, nitrogen base DNA 4 nitrogen bases: adenine,

guanine, thymine and cytosine ***Scientists knew DNA was made of

these parts- they did NOT know how all the pieces fit together!

“The race to build the 1st DNA model”

Rosalind Franklin

1) 2 strands like a twisted rope

2) Molecules were evenly spaced out…

2 Categories of Bases: Purines-

“larger bases”

adenine (A)

guanine (G) Pyrimidines-

“smaller bases”

cytosine (C)

thymine (T)

Chargaff’s Rule

Measured amounts of each base in various organisms and found:

amount of adenine (A) = thymine (T) amount of cytosine (C) = guanine (G)

This meant A only bonds T and C only bonds G

Structure of DNA Double helix- “spiral staircase”, 2 strands of

nucleotides “siderails” sugar and phosphate “rungs” bases (base pairs connected by hydrogen

bonds) bases attach sugar molecules, phosphate molecules

between sugars complementary- sequence of bases on one strand

determines the sequence of bases on other strand antiparrallel- strands are oriented opposite to each

other with respect to the carbon atoms in the sugar molecules

Watson and Crick “Double Helix”

Antiparallel- 5’ and 3’ ends

What is the job of all cells??? Process called Protein Synthesis: DNARNA Protein 2 stages: Transcription and Translation

RNA (Ribonucleic acid)

Nucleic acid… helps DNA make proteins _____RNA____vs._____DNA___

single strand double strand

sugar= ribose sugar= deoxyribose

A, C, G, U (uracil) A, T, C, G

mRNA, rRNA, tRNA “DNA is DNA”

all over nucleus only

Structure RNA

Transcription: Part 1 :Protein Synthesis Problem:

DNA (directions build protein) can not leave nucleus go to ribsome

Information DNA copied RNA (messenger)

DNA complementary mRNA occurs nucleus

Steps in Transcription 1st- DNA untwists 2nd- enzyme RNA polymerase

moves along DNA strand creating “complementary mRNA”

Genetic Code

Goal make protein protein - bunch amino acids every 3 bases (nucleotides) mRNA

code amino acid - called codon DNA: ATA CGG AAT (3

triplets) mRNA: UAU GCC UUA (3

codons)

What amino acids are needed to build the protein?

mRNA - UAU GCC UUA

Translation: Part 2:Protein Synthesis

Protein builtHappens ribosomerequires tRNA (transfer RNA) tRNA carries amino acids ribosomemRNA complementary tRNA

tRNA One end amino

acid Other end 3

bases called anticodon

anticodon complementary codon (mRNA/tRNA)

“safety check”

Steps Translation mRNA leaves nucleus goes ribosome (made

of rRNA) 1st- “start” codon 2nd- tRNA brings amino acids ribosome

(codons-anticodons pair) 3rd- bonds join amino acids 4th- stop codon ribosome releases protein cytoplasm

What is DNA Replication?

Process of “copying” DNA exactly Process must be completed before

cells can divide (reproduce) Multicellular organisms- cell division =

growth and repair/replacement Unicellular organisms- cell division =

reproduction

DNA Replication

DNA Replication (process) 1st- enzyme helicase

attaches to DNA and causes it to unzip at the replication fork (must break hydrogen bonds-bases)

2nd- enzyme DNA polymerase moves along leading strand adding complementary bases (continuously in 5’3’ direction toward replication fork)

3rd- lagging strand completed next but Okazaki fragments result (discontinuous away from replication fork)

4th- enzyme ligase joins the fragments on lagging strand Summary: 1 DNA molecule 2 DNA molecules

Mutations

If DNA does not get copied correctly, a mutation can arise.

Mutation- change in DNA sequence “Mutagens” are things found in the

environment that can get into your cells and “scramble” your DNA.

Three known mutagens:

1.) chemicals 2.) viruses 3.) UV radiation

Mutations – change in DNA

Substitution

Effects of Mutations… DNA carries instructions to build proteins. If the DNA is changed, proteins will be built

incorrectly. Two general types of mutations:

1. Gene mutation (effects one gene on chromosome)

2. Chromosome mutation Three different types of gene mutations

1. subsitution

2. Insertion

3. Deletion

Substitution

THE FAT CAT SAT

THE FAT RAT SAT

Changing one letter, changes one word, which changes the meaning of the sentence.

SubstitutionDNA: TAC GCA TGG AATMRNA: AUG CGU ACC UUAA.ACID: Met - Arg - Thr - Leu

DNA: TAC GTA TGG AATMRNA: AUG CAU ACC UUAA. ACID: Met - His - Thr - Leu

Results in one amino acid being altered

Insertion

THE FAT CAT SAT

THE SFA TCA TSA T

Inserting one letter, shifts all other letters over, creating several words to be incorrect. This is also known as a “frame-shift” mutation.

InsertionsDNA: TAC GCA TGG AATMRNA: AUG CGU ACC UUAA.ACID: Met - Arg - Thr - Leu

DNA: TAT CGC ATG GAA TMRNA: AUA GCG UAC CUU AA.ACID: Iso - Ala - Tyr - Leu

Results in several amino acids being altered

Deletion

THE FAT CAT SAT

THE ATC ATS AT

Similar to Insertion (frame-shift).

REMOVE

Deletion

DNA: TAC GCA TGG AATMRNA: AUC CGU ACC UUAA.ACID: Met - Arg - Thr - Leu

DNA: TAG CAT GGA ATMRNA: AUC GUA CCU UAA. ACID: Iso - Val - Pro - None

Results in several amino acids being altered

Significance of Mutations Some mutations may be “neutral,” they

won’t have an effect on the protein being built.

Some mutations can be very harmful and cause genetic disorders.

Some mutations lead to genetic variation in a species.

(Ex. Tongue rolling)