Transcript DNA and Individuality

GENE
EXPRESSION
HOW DOES DNA KNOW
WHEN TO MAKE A
PROTEIN?
DNA and
Individuality
Are all genes turned on in
all cells?
The answer is NO!
• Every body cell contains all DNA
• Cells “use” only genes specific for function
– EX. Red blood cells use only genes that make
it carry oxygen
– Can you list more examples?
• Skin cells only need proteins for structure and such
• Nerve cells only need proteins that enable them to
transmit impulses
**THEREFORE, NOT ALL DNA IS EXPRESSED
(MADE INTO PROTEIN) IN EVERY CELL!**
MUTATIONS
When DNA goes bad 
IMPORTANT FACT!
MUTATIONS MUST OCCUR
IN SEX CELLS IN ORDER
FOR THEM TO BE
PASSED ON TO NEXT
GENERATION!!!!!!!!!!
I REPEAT………………
ONLY MUTATIONS THAT
OCCUR IN EGG OR SPERM
CELLS CAN BE PASSED ON
TO OFFSPRING!!
(Have you ever heard of a
sperm fertilizing a skin
cell to make a baby??
That is silly!)
Chromosomal Mutations
• Change in # of chromosomes or
structure
–EX:
• NORMAL HUMAN BODY CELL =
46 Let’s see this!
• DOWN’S SYNDROME CELL =
47
Let’s see this!
Gene Mutations
• Change in actual DNA sequence
• **Review** What does DNA ultimately
code for?
Proteins
• Is construction of protein based on
original DNA strand?
Yes! (b/c it is what codes for mRNA)
Gene Mutations con’t…
• What would happen to protein made
if DNA sequence was changed?
–Wrong protein made
–Wrong shape of protein
• This would make protein
unusable!
Gene Mutations: Point
Mutations
1. POINT MUTATION:
• Base could be switched from one to another
– EX: TCA on DNA makes mRNA AGU
codes for Serine
» If T changed to G, would be CGU
which codes for
• Arginine
» Wrong AMINO ACID is coded for which
means, wrong SHAPE or PROTEIN is
made
Gene Mutations: Frame-Shift
2. FRAME-SHIFT:
– A base could be deleted or added
– EX: TCATTT on DNA;
• mRNA = AGUAAA codes for Serine +Lysine
• If the T is deleted in the DNA, now is GUAAA
• Ribosome will read GUA first which is for Valine
– Similar if a base is added
– Wrong AMINO ACID is coded for = wrong
PROTEIN made OR Translation will
abruptly STOP
Summary of Mutations
• Must occur in sex cells to be passed on
• Not all mutations are bad (depends on
environment)
• Ultimate source of variation within a
species!!!!!!
– Take humans for instance….do we all look
the same?????????
• Caused by:
– Exposure to radiation (ex. UV Rays)
– Exposure to certain chemicals (in cigarettes,
emitted from factories)
The Human Genome
Human Chromosomes (46 in a normal
human cell!)
• Two types:
– Normal chromosomes: 44 in each BODY
CELL; 22 in each GAMETE (sex cell)
– Sex chromosomes: 2 in each BODY CELL; 1
in each GAMETE (sex cell)
• MALE: X and Y
• FEMALE: X and X
• Chances for having a boy or a girl?
Chances for having a boy or
girl? 50% OF COURSE…LET’S
SEE!
X
X
X
Y
XX
XY
XX
XY
Environmental Expression
Some genes are “turned on”
under certain environmental
conditions
• EX. Himalayan Rabbit: Fur
changes color due to
TEMPERATURE change
– WARM = White fur (no pigment
produced)
– COLD = Black fur Why does
this make sense?
• Because black absorbs the heat,
helping little bunny rabbit to stay
warm