Unit 7 - DNA & Transcription - H Bio

DNA

universal genetic code

“Exons”

expressed segments

DNA is divided into A.

coding regions (genes)

• 1% of genome

Coding regions of DNA

• Code for RNA

• Code for regulatory proteins

• Code for proteins that directly/indirectly influence traits

Code for RNA

• tRNA, rRNA

• involved in protein synthesis

Code for regulatory proteins

affect gene expression; involved in cell specialization

Code for proteins that directly/indirectly influence traits

Ex.

• hormones (insulin & human growth hormone)

• enzyme (lactase & amylase)

• pigments (melanin & hemoglobin)

• structure (collagen & keratin)

Large % of our coding regions code for

identical proteins

DNA is divided into B.

noncoding regions

• 99% of genome

Noncoding regions of DNA are found between

genes and regions within genes (introns)

• INTRON = intervening segments

Noncoding regions of DNA determines

most of the diversity between individuals; leads to our unique “genetic fingerprint”

Transcription

the process of transforming a region of the DNA code (Gene) into messenger (mRNA) form

RNA polymerase binds to a specific region of DNA called the

promoter

In a eukaryotic cell,

each gene has its own promoter region

As RNA polymerase moves along the DNA molecule,

it causes a region of DNA, called a gene, to “unzip” into two separate, exposed strands

Promoter Region

marks the beginning of a DNA region (gene) that will be transcribed

Bases of RNA nucleotides found in the nucleus

bond to complementary bases found on one separated strand of DNA (called the template strand)

Separate RNA nucleotides are linked together by

an enzyme along the sugar-phosphate backbone to form a mRNA molecule

When a termination sequence of bases (the terminator) is reached on the DNA template strand,

RNA polymerase detaches and the newly formed pre-mRNA is released

Pre-mRNA transcript containing

both introns and exons is modified

Introns

intervening segments; removed from pre-mRNA

Exons

expressed segments; remain in completed RNA transcript

snRNPS bind together to form the

spliceosome

Resulting mature mRNA may then

exit the nucleus and be translated in the cytoplasm

5’ cap is added to

one end of the mature mRNA transcript

poly-A tail is added to

the 3’ end to form the mature mRNA transcript

Addition of cap and tail molecules to two ends of mRNA transcript

play a protective role, like a book’s front and back covers

mRNA travels through

nuclear membrane to ribosome

several more mRNA molecules will be

synthesized before DNA recoils

RNA transcript must be built in the

5’ → 3’ direction

Template strand must be built in the

3’ → 5’ direction

• opposite directionality of RNA transcript

In any cell, only

some genes are expressed:

• transcribed into mRNA and then translated into proteins

mRNA

transfers DNA code from the nucleus to the ribosome to be translated into proteins

rRNA

makes up the structure of the ribosome

tRNA

• transfers a specific amino acid to the correct matching position along the mRNA

• contains an anticodon

snRNA

small nuclear RNA:

• with proteins, forms spliceosome that aids in modification of RNA before it leaves nucleus