THE ROLES OF DNA

First Function: DNA Replication The Cell makes an identical copy of the DNA Takes place during the S phase of the Cell Cycle Carefully controlled by a group of enzymes

The Enzymes separate or unwind the 2 strands of DNA make 2 new strands by adding nitrogen bases according to the base pair rule the new strands are called “complimentary”

Write the Compliment DNA Code Strand of DNA _________________________________ ATT CGC ATC GGA TTC GCA AAC TTA __________________________________ Complimentary Strand of DNA

Write the Compliment DNA Code Strand of DNA _________________________________ ATT CGC ATC GGA TTC GCA AAC TTA TTA GCG TAG CCT AAG CGT TTG AAT __________________________________ Complimentary Strand of DNA

Mitosis Once DNA replication is complete a cell has duplicated all its genetic information The cell is ready to enter cell division Each daughter cell has an identical set of chromosomes 46 chromosomes

DNA Replication DNA replication is called semi-conservative That means the DNA for each daughter cell consists of 1 one old DNA strand and 1 new strand. This helps reduce the number of copy errors.

DNA REPLICATION

Review DNA Replication An exact copy of a cells chromosomes are made Requires enzymes Occurs during S phase Base pairs join following the base pair rule to form the new DNA strands A- T and C- G Results: each new daughter cell has a genetically identical set of chromosomes to the parent cell

Color DNA Replication Look back at your DNA structure coloring sheet for nitrogen base shape KEY Phosphates pink Deoxyribose blue Thymine orange Adenine green Guanines purple Cytosine yellow The boxed section shows 2 new strands of DNA. Color the old strands red and the new strands green

All Cells Need the Exact DNA Every daughter cell needs an exact copy of DNA because it contains the “Blue-print” of life or the instructions to make a living organism!

2nd Function: Protein Synthesis To decode the genetic information contained in DNA, the cell uses a molecule called RNA RNA = ribonucleic acid Carries out the instructions coded in DNA to make a protein What does RNA look like? We need to compare it to DNA for the answer……

DNA vs. RNA DNA Sugar = deoxyribose Double stranded Contains 3000 genes Bases = A T C G RNA Sugar = ribose Single stranded Contains 1 gene Bases = A U C G U= uracil

How Is RNA made?

RNA is made in a process called: Transcription Part of the nucleotide sequence of a DNA molecule is copied into RNA This sequence of DNA copied is called a gene DNA is a template from which RNA can be made

RNA Sequence RNA is constructed out of molecules in the Cell Requires enzymes RNA polymerase Produces a strand of RNA one base at a time RNA bases match the bases on DNA

Base Pair Rule for DNA coding into RNA RNA has Uracil (U) instead of Thymine (T) The base Adenine on DNA codes for Uracil on RNA The base Thymine on DNA codes for Adenine on RNA The base Guanine on DNA codes for Cytosine on RNA The base Cytosine on DNA codes for Guanine on RNA

Lets Practice DNA ___________________________ AAT CGT CTT GAC TGC TTC ____________________________ RNA What is the complimentary strand of RNA?

DNA transcribed into RNA AAT CGT CTT GAC TGC TAC UUA GCA GAA CUG ACG AUG ___________________________ RNA

New Strand is called mRNA Messenger (m) RNA = “cheap” copy of DNA Cell uses mRNA to transport DNA’s message

Questions 1. What is the purpose of mRNA? 2. How does mRNA carry DNA’s Message? 3. What does the message “say”?

1. What is the purpose of mRNA? mRNA Helps the Cell Make Proteins After DNA has coded for a strand of mRNA, it leaves the nucleus and travels to the ribosome At the ribosome mRNA’s code is translated into a protein mRNA codes for a specific protein by copying the DNA code!

2. How does mRNA carry DNA’s Message? RNA contains 4 different nitrogen bases (A,U,C,G) These 4 bases carry the instructions from DNA to assemble amino acids 3 nitrogen bases on RNA code for 1 amino acid The 3 nitrogen bases (AAA) are called a codon or a “word” in the genetic message How many amino acids would this code for? AAA CAC GGU

3. What Does DNA”s Message “Say”? the order of nitrogen bases on DNA specify a specific amino acid chain The chain of amino acids forms a protein If the DNA sequence changes then a different amino acid chain is made, creating a different protein

Amino Acids Basic structure

20 Amino Acids

Protein: Chain of Amino Acids How is a protein actually made?

Steps to Making a Protein Step 1: Transcription In the nucleus DNA unwinds at a very specific point mRNA is assembled by matching the bases on DNA following the base pair rule mRNA leaves the nucleus This process is called transcription DNA mRNA

Step 2: Translation At The Ribosome 1.mRNA arrives at the ribosome 2. mRNA’s code is read 3 bases at a time called a codon AAA = 1 codon 3. 1 codon represents 1 amino acid AAA = lysine CAT = histidine GGU = glycine 4. As the codon’s are read, a chain of amino acids form 5. The result is a molecule called a polypeptide chain

Translation The nucleotides in mRNA are translated into a polypeptide chain 1 Amino Acid at a time. Polypeptide chain Amino Acids mRNA Ribosome

Protein Synthesis Transcription Translation peptide bond video

Polypeptide Chain to Protein Polypeptide Twists and Folds Functional Protein Chain

Big Picture: Protein Synthesis The section of DNA (gene) directs the synthesis or making of a functional protein from inside the nucleus by using mRNA and a ribosome.

The Genetic Code A stretch of DNA: AAT GAC CAT GGC TAG codes for a different protein than a stretch that reads: GGG CCA TAG CGT ATT The 4 bases have endless combinations that form the 20,000 different proteins the human cell can synthesize

Genes and Proteins Genes: control your physical traits by coding for proteins that have specific functions in the body Proteins Molecules that control all cell functions DNA Video Clip

Putting It all Together Genes to Proteins Control physical characteristics: 3 examples A gene controls flower color by coding for an enzyme that produces a pigment A gene coding for an enzyme that controls blood type by producing complex molecules in the RBC A gene codes for a protein that regulates the rate and pattern of growth throughout an organism.

Gene Expression A gene that is transcribed into mRNA is said to be expressed or turned on A gene that is not being transcribed is said to be unexpressed or turned off Deciding which genes to turn on and which genes to turn off depends on the needs of the cell at that time.