WARM-UP: What does DNA stand for?

What is the purpose of DNA?

What is the structure of DNA and who figured it out?

DNA

CA Biology Standard- Genetics4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:

• a. Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA.

• b. Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.

• c. Students know how mutations in the DNA sequence of a gene may or may not affect the expression of the gene or the sequence of amino acids in an encoded protein.

What is DNA?

• DNA (Deoxyribonucleic acid) is the molecule that contains the genes of living things.

• It is in chromosomes inside the nucleus of eukaryotic cells. (In prokaryotes, it is free-floating in the cytoplasm.)

Animation: Human to DNA• http://www.pbs.org/wgbh/nova/genome/dna

.html#

Rosalind Franklin• In the 1950’s she used

X-Ray Diffraction to take a picture of the DNA molecule (long-ways).

What does Rosalind Franklin’s picture of DNA show?

• There are 2 strands.• The strands are

twisted around each other in a double helix.

• Nitrogenous bases are at the center of the molecule.

James Watson and Francis Crick

• They were working on figuring out the structure of DNA but couldn’t figure it out…

• When they saw Rosalind Franklin’s Picture of DNA, they figured out that it was a…..

• DOUBLE HELIX!

What is the structure of DNA?

• DNA is a double helix.• The double helix is wound

around proteins called histones.

• This forms a beadlike structure called a nucleosome.

• All packed together, this is chromatin.

• Chromatin winds together to form chromosomes.

Where is the ….

• Double helix?• Histone?• Nucleosome?• Chromatin?• Chromosome?

DNA Structure

• http://www.sumanasinc.com/webcontent/animations/content/DNA_structure.html

What is the structure of DNA?• Double helical ladder• ‘Backbone’ of ladder

is made of the sugar….

• Deoxyribose• And…• Phosphate!

What is the structure of DNA?

The ‘rungs’ of the ladder are made of nitrogenous bases …

Pyrimidines (single ring): • Thymine [T] and…• Cytosine [C]Purines (double ring):• Adenine [A]• Guanine [G] The purines and pyrimidines are held together by

hydrogen bonds.

What is the structure of DNA?

• A deoxyribose sugar, a phosphate and a base all together make up a…

• NUCLEOTIDE!

Build a DNA Model in Your Notebook

10 points

Cut out the nucleotides and match them up.

Paste the pieces of DNA into your

notebook.Answer the questions.

“Row, Row, Row DNA”

• We love DNAMade of nucleotides.Sugar, phosphate and a baseBonded down one side.

• Adenine and thymineMake a lovely pair.Cytosine without guanineWould feel very bare.

http://www.wtv-zone.com/REMEMBERTHEN/kidsmidi1/rowrow.mid

Chargoff’s Rules

• He found that the percentage of thymine was about equal to the percentage of adenine.

• And the percentage of guanine was about equal to the percentage of cytosine.

• Thus, they always pair with each other!

CHARGOFF’s RULE =BASE PAIRING RULE!

• Thymine always pairs with AdenineT-AA-T

• Cytosine always pairs with GuanineC-GG-C

Build a DNA Molecule

• http://learn.genetics.utah.edu/content/begin/dna/builddna/

Why would DNA need to replicate itself?

Why would DNA need to replicate itself?

• When a cell divides and replicates itself during mitosis, it needs to also replicate its DNA.

• During meiosis, the process of gamete formation, DNA needs to be replicated to pass genes onto offspring.

DNA Replication Overview The DNA molecule separates into 2 strands and then produces 2 new complementary daughter strands using the base-pair rule. Each strand of the double helix is a template for the new strand.

DNA Replication 1. The enzyme Helicase ‘unzips’ the double helix by

breaking the hydrogen bonds.2. The enzyme DNA Polymerase joins individual

nucleotides together, making the new strand of DNA.

DNA Replication Animation

• http://highered.mcgraw-hill.com/olc/dl/120076/micro04.swf

Paste the DNA strand into your notebook and write the complementary strand.

ATGGGCCTTAAACATTA

What is the difference between DNA and RNA?

DNA RNA

Structure

Function/Processes

Nitrogenous Bases

Type of Sugar

Location in Cell

Types

DNA RNA

Structure 2-stranded double helix

Function/Processes

Contains genes/instructions for cell

Nitrogenous Bases

Adenine, thymine, cytosine, guanine

Type of Sugar

Deoxyribose

Location in Cell

Nucleus

Types n/a

What is RNA?• Ribonucleic acid• Contains sugar ribose

(rather than deoxyribose)

• Is single-stranded rather than a double helix

• Contains adenine, cytosine, guanine and the base uracil rather than thymine

What is the function of RNA?• RNA is involved in

protein synthesis making a gene into a trait!

• It takes a copy of DNA out of the nucleus (because DNA is too big to leave the nuclear pores) and functions as a ‘working copy’ of DNA.

Types of RNA• Messenger RNA [mRNA]:

RNA that makes a copy of DNA and leaves the nucleus

• Ribosomal RNA [rRNA]: part of a ribosome, where protein synthesis occurs

• Transfer RNA [tRNA]: transfers amino acid to the ribosome as it is needed in the construction of a protein

Types of RNA

DNA RNA

Structure 2-stranded double helix Single stranded

Function/Processes

Contains genes/instructions for cell

Involved in protein synthesis

Nitrogenous Bases

Adenine, thymine, cytosine, guanine

Adenine, uracil, cytosine, guanine

Type of Sugar

Deoxyribose Ribose

Location in Cell

Nucleus Nucleus (mRNA), ribosome and cytoplasm (tRNA & rRNA)

Types n/a tRNA, mRNA, rRNA

HOW DO GENES BECOME TRAITS?

PROTEIN SYNTHESIS (GENE EXPRESSION)

1. TRANSCRIPTION2. TRANSLATION

Transcription• The process where mRNA molecules are

produced by copying part of the DNA molecule into a complementary sequence

How does transcription work?

• RNA polymerase binds to DNA and separates the strands. It then uses one strand of DNA as a template to assemble an RNA strand.– RNA polymerase only binds to regions of DNA

called promoters, areas with specific DNA base sequences.

RNA Editing

• Introns: sequences of DNA that do not code for a gene

• Exons: sequences of DNA that DO code for a gene

• When mRNA is created, the introns are cut out of it and only the exons are kept!

Translation• The process where the cell uses mRNA to

produce proteins. tRNA brings amino acids to the ribosome to match up with the mRNA.

The Genetic Code• Codon: 3 nucleotide

bases that code for a particular amino acid

• (1 codon = 1 amino acid).• AUG is the start codon.• 3 stop codons: UGA,

UAA, UAG.• Only 4 bases, but they

code for 20 different amino acids (protein sub-units)

• HOW? • 4x4x4= 64 possibilities

How does translation work?1. After transcription, mRNA attaches to the

ribosome.

How does translation work?2. Starting with the start

codon, AUG, in the mRNA the proper amino acid is brought to the ribosome by tRNA. That amino acid is attached to the polypeptide chain. Each tRNA molecule is specific to an amino acid. It has an anticodon that is complementary to the mRNA codon.

How does translation work?3. Polypeptide bonds are

created between amino acids, while bonds between tRNA and the amino acid are broken.

4. The process continues until tRNA hits a stop codon and the protein is assembled!

Protein Synthesis Wksht

15 points

REMEMBER:mRNA codes for amino acids using codons.

tRNA brings the amino acids to mRNA using anti-codons

Central Dogma Sing Along!

What is a mutation?

Mutations = changes in genetic material

• Mutations can be:– Advantageous– Deleterious– Have no effect

• Mutations are usually random and spontaneous, but they are sometimes caused by mutagens, chemical or physical agents that cause mutations.

Types of Mutagens

• Chemical Mutagens

– Example: nicotine, smoke, pesticides, methane, pollution

• Physical Mutagens

– Ultraviolet rays, radiation, extreme heat

• Biological Mutagens

– Bacteria, viruses

Mutagens

Mutagens that cause cancer are called carcinogens because they cause unregulated cell growth.Examples of carcinogens:– Poisons – Smoke in your lungs– Pollution – Radiation

Types of MutationsWhat is the difference between these two

statements?• My dog bit the cat.• My dog bit the car.This is a point mutation- a mutation involving

changes in one or a few nucleotides.Types of Point Mutations:• Insertion• Deletion• Substitution

Frameshift mutations are…

• When nucleotides are added or deleted, causing the whole reading frame to be shifted so that every amino acid is altered.

Gene Action/Mutations

15 pointsStaple into notebook when finished.

Translating a DNA Message

Make a DNA Keychain• Write a Key in your notebook.– Phosphate = big gold bead– Sugar = big green bead– Adenine = silver tube bead– Thymine = red tube bead– Guanine = dark blue tube bead– Cytosine = green tube bead

Instructions for DNA Keychains

• http://www.indiana.edu/~ensiweb/connections/genetics/beadproject/tpage.html