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#

DNA Structure

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

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?

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!

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.

Modeling Semi-Conservative Replication

10 pointsStaple into notebook

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) 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. Occurs in the ribosome of the cell.

The Genetic Code• Codon: 3 nucleotide

bases that code for a particular amino acid.

• AUG is the start codon.• There are 3 stop

codons too.• 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, 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

Central Dogma Sing Along!

What is a mutation?

Mutations = changes in genetic material

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

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

Mutagens

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

What 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.

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 points

Extra Credit: 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