GENE GENE EXPRESSIONEXPRESSION

HOW DOES DNA KNOW HOW DOES DNA KNOW WHEN TO MAKE A WHEN TO MAKE A

PROTEIN?PROTEIN?

DNA and DNA and IndividualityIndividualityAre all genes turned on in Are all genes turned on in

all cells?all cells?

The answer is NO!The answer is NO!

• Every Every body cellbody cell contains all DNA contains all DNA• Cells “use” Cells “use” only genes specific for functiononly genes specific for function

– EX.EX. Red blood cellsRed blood cells use only genes that make use only genes that make it carry it carry oxygenoxygen

– Can you list more examples?Can you list more examples?• Skin cells only need proteins for structure and suchSkin cells only need proteins for structure and such• Nerve cells only need proteins that enable them toNerve cells only need proteins that enable them to

transmit impulsestransmit impulses

**THEREFORE, NOT ALL DNA IS **THEREFORE, NOT ALL DNA IS EXPRESSED EXPRESSED (MADE INTO PROTEIN) IN EVERY CELL!**(MADE INTO PROTEIN) IN EVERY CELL!**

MUTATIONSMUTATIONS

When DNA goes bad When DNA goes bad

IMPORTANT FACT!IMPORTANT FACT!

MUTATIONSMUTATIONS MUST MUST OCCUROCCUR IN IN SEX CELLSSEX CELLS IN ORDER IN ORDER

FOR THEM TO BE FOR THEM TO BE PASSED ONPASSED ON TO NEXT TO NEXT GENERATION!!!!!!!!!!GENERATION!!!!!!!!!!

I REPEAT………………

ONLY ONLY MUTATIONSMUTATIONS THAT THAT OCCUR IN OCCUR IN EGGEGG OR OR SPERMSPERM CELLS CAN BE PASSED ON CELLS CAN BE PASSED ON

TO TO OFFSPRINGOFFSPRING!!!!

(Have you ever heard of a (Have you ever heard of a sperm fertilizing a skin sperm fertilizing a skin cell to make a baby?? cell to make a baby??

That is silly!)That is silly!)

Chromosomal MutationsChromosomal Mutations

• Change in # of chromosomes or Change in # of chromosomes or structurestructure

–EX:EX:

• NORMAL HUMAN BODY CELL = NORMAL HUMAN BODY CELL = 4646 Let’s see this!

• DOWN’S SYNDROME CELL = DOWN’S SYNDROME CELL = 4747

Let’s see this!

Gene Mutations

• Change in actual DNA sequenceChange in actual DNA sequence

• **Review** What does DNA ultimately **Review** What does DNA ultimately code for?code for?

ProteinsProteins

• Is construction of protein based on Is construction of protein based on original DNA strand?original DNA strand?

Yes! (b/c it is what codes for mRNA)Yes! (b/c it is what codes for mRNA)

Gene Mutations con’t…Gene Mutations con’t…

• What would happen to protein made What would happen to protein made if DNA sequence was changed?if DNA sequence was changed?

–Wrong protein madeWrong protein made

–Wrong shape of proteinWrong shape of protein

• This would make protein This would make protein unusable!unusable!

Gene Mutations: Point Gene Mutations: Point MutationsMutations

1.1. POINT MUTATIONPOINT MUTATION:: • Base could be switched from one to anotherBase could be switched from one to another

– EXEX:: TCA on DNA makes mRNA AGU TCA on DNA makes mRNA AGU codes for codes for SerineSerine

» If If T changed to GT changed to G, would be , would be CGUCGU which codes for which codes for

• ArginineArginine» Wrong Wrong AMINO ACIDAMINO ACID is coded for which is coded for which

means, wrong means, wrong SHAPESHAPE or or PROTEINPROTEIN is is mademade

Gene Mutations: Frame-ShiftGene Mutations: Frame-Shift

2. FRAME-SHIFT:2. FRAME-SHIFT: – A base could be deleted or added A base could be deleted or added

– EX:EX: TCATTTTCATTT on DNA; on DNA; • mRNA = mRNA = AGUAAAAGUAAA codes for codes for Serine +LysineSerine +Lysine• If the If the T is deletedT is deleted in the DNA, now is in the DNA, now is GUAAAGUAAA• Ribosome will read Ribosome will read GUAGUA first which is for first which is for ValineValine

– Similar if a base is Similar if a base is addedadded

– WrongWrong AMINO ACIDAMINO ACID is coded for is coded for == wrong wrong PROTEINPROTEIN made made OROR Translation will Translation will abruptly abruptly STOPSTOP

Summary of MutationsSummary of Mutations• Must occur in Must occur in sex cellssex cells to be passed on to be passed on• Not all mutations are badNot all mutations are bad (depends on (depends on

environment)environment)• Ultimate source of variationUltimate source of variation within a within a

species!!!!!!species!!!!!!– Take humans for instance….do we all look Take humans for instance….do we all look

the same?????????the same?????????

• Caused byCaused by::– Exposure to radiation (ex. UV Rays)Exposure to radiation (ex. UV Rays)– Exposure to certain chemicals (in cigarettes, Exposure to certain chemicals (in cigarettes,

emitted from factories)emitted from factories)

The Human GenomeThe Human Genome

Human Chromosomes (46 in a normal Human Chromosomes (46 in a normal human cell!)human cell!)

• Two typesTwo types::– Normal chromosomes:Normal chromosomes: 44 in each BODY 44 in each BODY

CELL; 22 in each GAMETE (sex cell)CELL; 22 in each GAMETE (sex cell)– Sex chromosomes:Sex chromosomes: 2 in each BODY CELL; 1 2 in each BODY CELL; 1

in each GAMETE (sex cell)in each GAMETE (sex cell)• MALE:MALE: X and Y X and Y• FEMALE:FEMALE: X and X X and X• Chances for having a boy or a girl?Chances for having a boy or a girl?

Chances for having a boy or Chances for having a boy or girl? 50% OF COURSE…LET’S girl? 50% OF COURSE…LET’S SEE!SEE!

XX YY

XX

XX

XXXX

XXXX XXYY

XXYY

Environmental Environmental ExpressionExpressionSome genes are “turned on” Some genes are “turned on”

under certain environmental under certain environmental conditionsconditions

• EX. Himalayan Rabbit:EX. Himalayan Rabbit: Fur Fur changes color due to changes color due to TEMPERATURE changeTEMPERATURE change– WARMWARM = White fur (no pigment = White fur (no pigment

produced)produced)– COLDCOLD = Black fur Why does = Black fur Why does

this make sense?this make sense?• Because black absorbs the heat, Because black absorbs the heat,

helping little bunny rabbit to stay helping little bunny rabbit to stay warmwarm