STORES AND PASSES ON GENETIC INFORMATION FROM ONE GENERATION TO ANOTHER .

DNA DEOXYRIBONUCLEIC ACID

DNA STRUCTURE

-THE DNA structure is shaped like a spiral staircase or a twisted ladder.-This Double Helix Model was discovered by James Watson and Francis Crick in 1953.

DNA STRUCTURE

- The legs of the ladder are made of alternating sugars (deoxyribose) and phosphates.- The rungs of the ladder are made of nitrogen bases. There are four types of nitrogen bases in DNA.- The sugar, phosphate, and base is called a nucleotide.

DNA STRUCTURE

The four nitrogenous bases are:• ADENINE = A• GUANINE = G• CYTOSINE = C• THYMINE = T

THEY ARE REPRESENTED BYTHEIR CAPITAL LETTER.

DNA STRUCTURE

There are two sides to the ladder (imagine the ladder cut down the middle of the rungs). One half of the rung is one base and the other half is that base’s compliment.

Adenine always pairs with ThymineCytosine always pairs with Guanine

DNA STRUCTURE

The order of the nucleotides make genes and these code for our individual characteristics.

The number of possible combinations seems never ending.

For example: ATCGTCAGG could be part of a code for the gene that regulates unattached and attached ears.

DNA REPLICATIONREPLICATION: Is the process where DNA forms exact copies using one half of the ladder as a template.

DNA REPLICATION

1. The enzyme Helicase splits the original strand in half. Like unzipping a zipper.

2. The enzyme DNA Polymerase takes free floating nucleotides and binds them to the template.

3. Each original strand now has combined with

nucleotides and formed a new strand.

4. Half of each new strand of DNA is the original copy.

Transcription and Translation

• RNA• In order for the information contained in segment

of DNA to be useful we have to have RNA.• RNA is like DNA but it differs in three ways:

– 1. RNA consists of only one strand (like one side of an unzipped zipper).

– 2. The sugar backbone is made of ribose and not deoxyribose

Transcription and Translation

– 3. RNA has four base pairs but it does not have thymine. Thymine is replaced by another base called Uracil (for short U). It forms a base pair with adenine just like thymine did.

Transcription and Translation

• What does RNA Do?– RNA takes the message from the DNA and uses

it to assemble the amino acids into proteins.

Transcription and Translation

• Types of RNA Used– There are three types of RNA:– 1. Messenger RNA (mRNA) Takes info from

the DNA in the nucleus to the cytoplasm.– 2. Ribosomal RNA (Ribosomes) attach to the

mRNA and reads the message to assemble the amino acids in the correct order.

– 3. Transfer RNA (tRNA) Transfers amino acids to the ribosomes for assembly

Transcription and Translation

• Transcription• In transcription a segment of DNA is used to make

an RNA copy.– Steps– 1. Enzymes unzip a segment of DNA just like in DNA

replication.– 2. RNA nucleotides pair up with the DNA nucleotides.

Guanine with cytosine and adenine withuracil.– 3.The RNA breaks away as the DNA zips back together.

This becomes messenger RNA as it goes to the cytoplasm.

Transcription and Translation

• The Code– There are 20 different amino acids and four bases so the

bases have to code for certain amino acids based on their order or sequence.

– Three nucleotides(bases) code for one amino acid.– For example if three uracil appear together it codes for the

amino acid phenylalanine.– Each group of three bases coding for an amino acid is

known as a codon.– There are sixty four combinations possible when using a

sequence of three bases. Therefore there are 64 mRNA codons in the genetic code.

Transcription and Translation

• The code continued– Not all codons code for amino acids. Some code for

instructions. UAA codes to stop assembly of the protein and Aug codes for the start.

– There can be more than one code for an amino acid. See page 298 for example codons and the amino acids they code for.

– This code is universal because the same codons code for the same proteins in all living things.

Transcription and Translation

• Translation: The process of taking information from the mRNA and turning it into a protein

• See Mini Lab 11-1 on page 299– Transfer RNA takes the free floating amino acids to the

mRNA. Each tRNA attaches to one specific amino acid for transport.

– On the end opposite the amino acid the tRNA has a series of three nucleotides (called the anticodon) that ensure the tRNA locks into the correct place on the mRNA

– The tRNA with the anticodon and amino acid find the rRNA (ribosome locked on the mRNA) and locks on.

Transcription and Translation

• Translation (the end)– The rRNA slides to the next codon another tRNA

molecule with a matching anticodon locks on.– An enzyme locks the two amino acids together with a

peptide bond. After the bond is formed the first tRNA releases from the mRNA leaving it’s amino acid behind. It is free to go join up with a new amino acid and continue the process.

– This continues until the ribosome hits the stop codon. The chain of amino acids is released as a protein enzyme. The protein coils in the same orientation every time.