DNA and Genes

The Structure of DNA• DNA is a type of nucleic acid • DNA is made of subunits called nucleotides• Strand of DNA looks like a 3D-double helix shape• Nucleotides have 3 parts (will draw this on next slide)

– 1.Sugar • 5 C sugar called deoxyribose

– 2.Phosphate group– 3.Nitrogen Base (4 different types)

• Adenine (A) • Guanine (G)• Thymine (T)• Cytosine (C)

Base pairing rules

• 1 molecule of human DNA contains billions of nucleotides

• Adenine=Thymine• Guanine=CytosineThese are known as Chargaff’s rules

The DNA Song(to the tune of Row, Row, Row your Boat)

• We love DNA• Made of nucleotides.

• Sugar, phosphate, and a base,• Bonded down one side.

•  • Adenine and thymine• Make a lovely pair,

• Cytosine without guanine• Would feel very bare.

•  • (author unknown)

•  •  

The Double Helix

• Watson and Crick

• 2 strands of DNA wind around each other– twisted – like a twisted ladder

• They fit together using base pairs and have a sugar-phospate backbone

• What if one strand is ACACAC, what would the other strand be?

• +++++++++++++++++++++++++++++++++++

summary

• The DNA molecule is a long chain of subunits called nucleotides. Each nucleotide is made of a phosphate group, the five-carbon sugar deoxyribose, and one of the four different nitrogen bases.

• Stop**********************************

QSR #3

• 1. What are the 3 parts of a nucleotide?___________, _____________, _______________.

• 2. a. DNA is in a ____ ____ shape.• b. _______ & _______ discovered this shape.• 3. What are the base pairing rules for nucleotides?• 4. If one strand of DNA is ACGTAGCTAG, the

complementary strand = _________________.

Replication of DNA• Process by which DNA is copied within the

NUCLEUS….during which phase? __________

• Single strand serves as a “template” or pattern for next strand

• Can occur over and over again

Steps of Replication (S-Phase)

– 1. Helicase (an enzyme) unzips the helix into separate strands

– 2. Forms a “bubble” where it’s replicating– 3. Another enzyme, DNA Polymerase, pairs free

nucleotides to the template– 4. Now have two identical strands of DNA that are

ready to start cell division (mitosis)…each with an old strand of DNA & a new strand of DNA

Replication of DNA

• DNA Polymerase:– Allows for “proofreading”– if a wrong nucleotide gets

added, DNA polymerase removes it and adds the correct one

                                                                                                             

Summary

• In DNA replication, enzymes work to unwind and separate the double helix and add complementary bases to the exposed strands. Each new double helix is composed of one old DNA strand and one new DNA strand.

QSR #4• 1. a. When would a DNA molecule need to replicate itself?• ____________________ b. and in what stage does this occur?

________________________• 2. What would you call a molecule with a RIBOSE sugar and

THREE phosphate groups?_____• 3. If a DNA molecule is 40% cytosine, what % is thymine?

_________• 4. Define replication.____________________________• _____________________________________________• 5. DNA _________ adds free nucleotides to the parental strand of

DNA, then “___________” to make sure its done correctly.

QSR #5

• 1. Fill in the blanks of the following paragraph:– Steps of replication: The _________ enzyme unzips

the double stranded ______. A __________ forms where this occurs. DNA______________, another enzyme, adds the correct _____________ to both of the unwinded strands. It also acts as a _______________...it corrects incorrect nucleotides. There are now ____ strands of exact copies of ______.

“Central Dogma” of Molecular Biology

• States that information flows from DNA, to RNA, then to proteins being made.

RNA

• Like DNA, RNA is made of nucleotides (sugar, phosphate, and base)

• It is a “temporary copy” of DNA that is used, then destroyed

• Single-stranded – RIBONUCLEIC ACID

• Why is RNA needed?_____________________

Transcription

• A process that uses “some” DNA to make a complimentary single strand of RNA

3 Types of RNA• Messenger RNA (mRNA)

– The message in DNA is rewritten in this form INSIDE THE NUCLEUS and taken to the ribosome

• Transfer RNA (tRNA) – Transfers amino acids within a ribosome to make

proteins.

• Ribosomal RNA (rRNA)– The ribosomes that actually make the protein– (ribosomes are made or RNA and PROTEIN)

Transcription Steps:

****Same steps as replication to make RNA: – 1. RNA polymerase unzips the DNA– 2. use template to make a complementary base-pair– 3. RNA polymerase “Proofreads” RNA base pairs– 4. this new single strand of mRNA detaches from the

DNA, and the DNA “zips”back up– 5. FINAL STEP: RNA strand ( called mRNA) can

now leave the nucleus and be “translated” into a protein

DNA is the blueprint for Proteins

Transcription

• DNA is found in the nucleus, but is too big to leave the nucleus– BUT….DNA has the instructions to make proteins– AND, protein synthesis takes place at the ribosome—

(cytoplasm/Rough ER)

• How does the information get from nucleus to ribosome?---mRNA

• +++++++++++++++++++++++++++++++++++

QSR #6

• 1. The _____ ______ of molecular biology states that info flows from DNA, to RNA, to proteins.

• 2. Ribonucleic acid is also called ____ for short.• 3. _______ is the process of copying a strand of DNA to make a

mRNA.• 4. Very important enzymes involved in DNA/RNA synthesis are

__________(s).• 5. What’s the point for making RNA?_______________________• 6. How do DNA instructions get from the nucleus to the ribosome?

___________

The difference(between DNA & RNA)

• *****1. U replaces T in RNA…”Uracil” binds now with adenine…

• 2. Also the sugar in RNA is ribose, not deoxyribose• 3. Remember that RNA is only a SINGLE STRAND!!!• 4. RNA IS ONLY TEMPORARY!!!!

– If a DNA segment = AGCCTAA, what would be the mRNA molecule?__________________

Review before notes:

• 1.True or false…DNA can leave the nucleus, taking its genetic info with it in order to make some proteins.

• 2. Why does a cell make lots of RNA but only one copy of DNA?

• 3. What would be the complimentary strand of RNA if the DNA sequence is ACCTTTGAAA?

• 4. What happens to the DNA molecule once it makes a strand of RNA?

Translation

• A lot of DNA is nonsense and codes for nothing – “junk DNA” or “INTRONS”

• “EXONS” are regions of DNA that do code for proteins

• Translation: the process of “translating” info from mRNA to make a protein.– This occurs on ribosomes!!!– Where does transcription take place? ____________

Practice

• Original DNA segment: ACCGTATTATTACGG• Complimentary mRNA: ____________________

– What is this called?___________________________

• Complimentary tRNA: _____________________– What is this called? ___________________________

• So how does tRNA compare to DNA?

• +++++++++++++++++++++++++++++++++++

Translation…

• Codon: 3 nucleotides make up a “word”

• Example: Serine (Amino Acid) have the codons UCU, UCC, UCA, UCG– 1Start codon: AUG -- signal for start of translation– 3 Stop codons: UGA, UAA, UAG -- signal for

stop/end of amino acid chain

• (look at handout)

Use your worksheet…

• What Amino Acid is coded by GGA? UGG? ACU?

• Amino acids are then linked together to become a ___________, which then is used to build the entire organism

• ****20 amino acids make up a protein****

• +++++++++++++++++++++++++++++++++++

Genetic Changes

• Mutation– Any change in the DNA sequence that also changes

the protein it codes for

• ***Mutations in reproductive cells WILL be passed to offspring• ***Mutations in body cells could cause problems for the individual but WILL NOT be passed to offspring

Point Mutations

• A change in a single base pair in DNA• THE DOG BIT THE CAR• THE DOG BIT THE CAT

– GGC CHANGES TO AGC– GLY CHANGES TO SER

• CAN EFFECT THE ENTIRE FUNCTION OF THE PROTEIN– ****Least harmful of the mutations****

Frameshift Mutations

• A mutation in which a single base is added or deleted

• THE DOG BIT THE CAT

• THE DOB ITT HEC AT

• Every codon after the addition or deletion is effected

Causes of Mutations

• 1. Mutagens—agents in the environment that can

change DNA…ex: UV from sun– Any agent that can cause cancer

• 2. Radiation– X-rays– Cosmic ray– UV rays

Causes of Mutations

• 3. Chemicals– Asbestos– Cyanide– formaldehyde

• 4. High temperatures

Repairing DNA

• Enzymes proofread DNA and replace incorrect nucleotides with correct nucleotides– DNA polymerase– RNA polymerase

Study Guide

Structure of DNA1. nucleotides2. Base pairing rules3. Double helix• Replication

Transcription• translation• Mutations• ***know all your notes and QSR!!!