Chapter 13By Mrs. Pires

Proteins

The human body is basically a bunch of proteins working together in a huge chemical reaction.

DNA holds all the information (recipe) to make all the proteins in the body.

The DNA is located in the nucleus but the protein factory is the ribosome.

The DNA is too big and has too many responsibilities to leave the nucleus and go to the ribosomes to drop off a protein recipe.

DNA needs the help of a messenger!

Some background information….

The messenger RNA (mRNA) is like a disposable piece of DNA.

mRNA is assembled inside the nucleus from individual sugars, phosphates and bases that are floating around.

These pieces are put together in a specific order by copying a complimentary sequence of the DNA (which holds the protein recipe needed).

This is called transcription.

Some more background information….

After the protein recipe is copied down by the mRNA, the messenger RNA leaves the nucleus and heads to the ribosome’s protein-making factory.

Proteins are made in a process called Translation.

Characteristic DNA RNA

Shape Double helix Single helix

Location In Nucleus

In Nucleolus, cytoplasm, or ribosome

Sugar Deoxyribose Ribose

Types 1 type 3 types

BasesAdenine, Thymine,

Guanine, CytosineAdenine, Uracil,

Guanine, Cytosine

TYPEMessenger RNA

(mRNA)Transfer RNA

(tRNA)Ribosomal RNA

(rRNA)

Location nucleoluscytoplasm &

ribosome ribosome

Function

Copies the protein

recipe from the DNA strand

rewrites the recipe from the mRNA

into a language the ribosome will understand

part of ribosome structure

Shape Single helix

Cloverleaf, “hairpin”, inverted

“L” shape Globular shape

mRNA: tRNA:rRNA:

Every 3 bases in the DNA (and mRNA) is called a codon.

Every codon codes for one amino acid.

Amino acids link together to form protein like beads on a string.

There are 23 basic amino acids in the body.

DNA CODONSRNA CODONS

An enzyme called RNA polymerase unwinds a section of DNA to be copied.

One strand of the DNA double helix is used as a template (The template strand is also called the antisense strand)

RNA polymerase binds to the “start codon” (promoter) at the beginning of a desired recipe on the DNA strand.

The START (promoter) codon is TAC on the DNA strand.

The mRNA strand copies the

codons from the DNA using complementary base pairing until it gets to:

One of the STOP codons (ACT, ATT, or ATC).

These are also called repressors or terminator sequences.

The stretch of DNA that is transcribed into an RNA molecule is called a transcription unit.

TAC is the start codon

ACT, ATT, & ATC are the STOP codons

dna ATG CCG GTA CTT TCC CGT TAA

dna TAC GGC CAT GAA AGG GCA ATT

mRNA              

tRNA              

Amino acid sequence              

This completed mRNA migrates from the nucleus to the cytoplasm and heads to the ribosome.

The strand of mRNA is called the codon sequence (codon language).

http://youtube.com/watch?v=OtYz_3rkvPk&feature=related

The mRNA gives the recipe to the ribosome to produce the protein. However, there is a problem.

The ribosome does not understand the codon language that the recipe is written in.

Never fear…help is on the way in the form of Transfer RNA!

tRNA

Transfer RNA (tRNA) is able to translate the codon language to the anticodon language so the ribosome can read it.

The ribosome binds to the mRNA at the start codon (AUG) that is recognized only by the initiator tRNA.

mRNA

The mRNA rolls between the two units on the ribosome.

< AUG

In this process, each set of 3 mRNA bases (the mRNA base triplet is called a codon) will pair with a complimentary tRNA base triplet (3 bases) called an anticodon. 

http://biology.kenyon.edu/slonc/bio3/ribo/ribo1.html

http://www.sciencenetlinks.com/interactives/protein.html

http://www.youtube.com/watch?v=XuUpnAz5y1g&feature=related

Each tRNA is specific to an amino acid. As tRNA's are added to the sequence, the amino

acids begin to link together by peptide bonds as it grows.

The amino acid (peptide chain) will continue to grow until it reaches the stop codon on the mRNA.

Since there is no stop anticodon (tRNA) to match the stop codon, the ribosomal complex falls apart.

The amino acid chain, now called a protein chain, is release into the cell.

www.wiley.com/legacy/college/boyer/0470003790/structure/tRNA/trna_intro.htm

1. Type in the link below:

2. Scroll down to page 2 where you will find the diagram below.

3. Click on “protein synthesis animation” under the diagram online.

4. Go through the Overview and Basic tutorials.

5. Complete the first two interactive activities dealing with the mRNA/amino

acid chart. Put your answers on the back of this paper.

DNA   CAT     TAT      

mRNA       CUC       UAA

tRNA UAC   GAU       CUA  

a.a.           TRY    

DNA: TAC GGA TCT GTA CTT ACG ACT mRNA: ___ ____ ___ ____ ___ ____ ___ tRNA: ___ ____ ___ ____ ___ ____ ___ a.a.: ___-____ -___ -____-____-____-___

* Remember: the chart is based on mRNA.

DO NOW!

Are heritable changes in genetic information

Two types: 1. Gene mutations (a.k.a. Point

mutations)2. Chromosomal Mutations

http://www.pbs.org/wgbh/nova/genome/media/2809_q056_13.html

Include: 1. Substitutions (one base is changed

into another)

2. Insertion results in a frameshift3. Deletion

This type of mutation is called a frameshift. Frame 1: AAU GCG GAC UAA --- asparagine ---- alanine ---- aspartate ---- stop Frame 2: A AUG CGG ACU AA ---methionine ---- arginine --- threonine--- Frame 3: AA UGC GGA CUA A

Four main types:◦ Deletion◦ Duplication◦ Inversion◦ Translocation

Lets take a look---------------------

Some or all of the genes on a chromosome become reversed.

THE CAT ATE THE FAT RAT could become….

THE TAC ETA EHT TAF RAT

Some or all of the genes on a chromosome are deleted.

THE CAT ATE THE FAT RAT could become….

THE CAT RAT

Some or all of the genes on a chromosome are doubled.

THE CAT ATE THE FAT RAT could become….

THE CAT CAT ATE THE FAT FAT RAT

Some or all of the genes on two different chromosomes either switch places like this:

1)THE CAT ATE THE FAT RAT2)THE RAT ATE THE HAT could become….

1) THE RAT ATE THE HAT RAT

2) THE CAT ATE THE FAT

or some genes from one chromosome transfer to another like this:

1) THE CAT ATE THE FAT RAT2) THE RAT ATE THE HAT could become….

1) THE CAT ATE THE…2) THE RAT ATE THE HAT FAT RAT

Brac 1: http://www.youtube.com/watch?v=4bGkUQBw1Rs

Sickle Cell and Malaria: http://www.pbs.org/wgbh/evolution/library/

01/2/l_012_02.html

Gene A

DNA: ACC GGT TAT

mRNA:

tRNA:

A.A sequ:

Trait:In this lab, the chart is basd on tRNA not mRNA

Gene A Gene B

DNA ACC GGT TAT DNA AGC CGA

mRNA   mRNA  

tRNA   tRNA  

a.a sequ.   a.a sequ.  

Trait   Trait  

Gene C Gene D

DNA TTT AAC DNA GGA CGC CGA

mRNA   mRNA  

tRNA   tRNA  

a.a sequ.   a.a sequ.  

Trait   Trait  

Gene E Gene F

DNA GGG AGG AAA CCC DNA ATC ATC CTA

mRNA   mRNA  

tRNA   tRNA  

a.a sequ.   a.a sequ.  

Trait   Trait  

Gene G Gene H

DNA   DNA  

mRNA   mRNA  

tRNA   tRNA  

a.a sequ.   a.a sequ.  

Trait   Trait  

DNA: TAC GGA TCT GTA CTT ACG ACT mRNA: ___ ____ ___ ____ ___ ____ ___ tRNA: ___ ____ ___ ____ ___ ____ ___ a.a.: ___-____ -___ -____-____-____-___

* Remember: the chart is based on mRNA.

DO NOW!

http://science.discovery.com/videos/creating-synthetic-life/