DNA Notes DAY 2Replication, overview of transcription,

overview of translation

• WARM UP

• What is the base pairing rule?

• Who created it?

How DNA is Copied• DNA is double stranded – base pairing allows for

easy copying; one strand serves as a template for a new strand

• Replication – the process of making a new DNA strand

• DNA double helix is unwound by an enzyme called a helicase. Helicase breaks hydrogen bonds linking the nitrogen bases

• The point where the helix separates is called the replication fork.

• At the fork; enzymes called DNA polymerase moves along the strands, reading the nitrogen base of each nucleotide, and adds the complementary nucleotide to the new strand

• DNA polymerase will proofread – it will only add a new nucleotide if the previous one was added correctly following the base pair rules

• Replication occurs in many places within the strand. It does not start at one end and end at the other; but occurs in segments

Steps for Replication1. DNA helicase unzips the DNA by breaking the

hydrogen bonds holding the bases together

2. The two strands unwind creating a replication fork.

3. Each strand serves as a template so the correct pair can come in and bind to the strands

4. DNA polymerase joins the nucleotides together and proofreads the new strand. Proofreading improves the odds of not having mistakes in the DNA

5. Two identical DNA molecules are made

• Cells turn the information found within the genes on DNA into a set of instructions for use in building proteins.

• This set of instructions of the gene is called ribonucleic acid or RNA.

• RNA is a single strand of nucleotides; DNA is double stranded

• The sugar in RNA is a 5 Carbon sugar called ribose; DNA’s sugar is deoxyribose

• RNA does not contain Thymine, but has replaced Thymine with the base Uracil

The Path of Genetic Information

DNA compared to RNA

DNA RNA

How many strands?

2 1

Nucleotide subunit

Deoxyribose sugar Ribose sugar

Bases Thymine (T)

Adenine (A)

Guanine (G)

Cytosine (C)

Uracil (U)

Adenine (A)

Guanine (G)

Cytosine (C)

Phos-

phate Group

Deoxy-ribose Sugar

Nitro-genBase Phos-

phate Group

Ribose Sugar

Nitro-genBase

T – A

G – C

U – A

G – C

There are 3 forms of RNA

1. mRNA = messenger RNA2. tRNA = transfer RNA3. rRNA = ribosomal RNA

• All 3 RNA’s are responsible for processing the information in a gene into protein, this process is

GENE EXPRESSION

• Gene expression occurs in 2 stages. 1. Transcription (RNA is made)

2. Translation (protein is made)

Transcription: Making RNA

• Transcription takes place inside the nucleus

• RNA is made in the form of mRNA.

• It has a U (uracil) instead of T (thymine)– A now pairs with U

• DNA: GAG AAC TAG TAC

• RNA: CUC UUG AUC AUG

Three Types of RNA

• mRNA – used as a blueprint or template for a protein; carries DNA’s information to site of translation

• tRNA – decodes mRNA into amino acid sequences

• rRNA – RNA part of a ribosomes structure.

The Genetic Code

• Instructions on mRNA are written as a series of three nucleotide sequences called a codon.

• Each codon (every three nucleotides) corresponds to a certain amino acid or a stop signal

• 64 possible codon combinations

Translation: Making Proteins • Takes place in the cytoplasm• mRNA carries the code so that proteins can be

made. • tRNA tranlates that code and turns it into protein.

Genes and Proteins

• Genes contain nothing more than the instructions for assembling proteins

• Proteins are the keys to almost everything that living cells do

• Many proteins are enzymes which catalyze and regulate chemical reactions

Examples of enzymes determining characteristics

• An enzyme produces the pigment that makes a flower red

• An enzyme produces an antigen on your red blood cells determining your blood type

• Enzymes control the growth, shape, and size of your cells

Human Genome clip