We lose from 30,000-40,000 cells/day……these need to get replaced

Before a cell duplicates, it makes an exact copy of its DNA for new cell Double helix “unzips” through an enzyme

(helicase) that breaks H bonds DNA polymerase attaches nucleotides to

DNA strand to form complementary strands

DNA never leaves the nucleus, is protected RNA is a copy of DNA that goes out of

nucleus to give cell instructions to make proteins

3 Main Differences between RNA to DNA Single stranded, smaller Contains ribose sugar Contains uracil in place of thymine

Ribose Sugar

Adenine: AUracil: UGuanine: GCytosine: C

DNA unzips at site of desired gene at promoters (specific base sequence signal for start)

RNA polymerase creates a complimentary strand of gene with RNA nucleotides

mRNA leaves nucleus to ribosome for protein synthesis

Sometimes in the RNA copy, there are some portions that don’t code for the protein (introns)

Introns get discarded and remaining portions (exons) of RNA get spliced back together.

Transcription happens in the nucleus. An RNA copy of a gene is made.

Then the mRNA that has been made moves out of the nucleus into the cytoplasm

Once in the cytoplasm, the mRNA is used to make a protein

Cytoplasm of cell

Nucleus

DNAmRNA

mRNA

Messenger RNA (mRNA)- carry info on polypeptide synthesis from nucleus to ribosomes

Ribosomal RNA (rRNA)- make up subunits that make ribosomes

Transfer RNA (tRNA)- bring amino acids to the ribosome and matches them to coded mRNA message

Table 14.2Types of RNA

Type of RNA Functions in Function

Messenger RNA(mRNA)

Nucleus, migratesto ribosomesin cytoplasm

Carries DNA sequenceinformation to ribosomes

Transfer RNA(tRNA)

Cytoplasm Provides linkage between mRNAand amino acids;transfers aminoacids to ribosomes

Ribosomal RNA(rRNA)

Cytoplasm Structural component of ribosomes

*Ribosome binds to mRNA in cytoplasm

•Genetic code is read in words that are 3 letters long called CODONS

• Each codon codes for an AMINO ACID

U C A G

U

C

A

G

GACU

GACU

GACU

GACU

UUUUUCUUAUUG

CUUCUCCUACUG

AUUAUCAUAAUG

GUUGUCGUAGUG

phe

leu

leu

ile

met (start)

val

UCUUCCUCAUCG

CCUCCCCCACCG

ACUACCACAACG

GCUGCCGCAGCG

ser

pro

thr

ala

UAUUACUAAUAG

CAUCACCAACAG

AAUAAC

AAGAAA

GAUGACGAAGAG

tyr

stopstop

his

gln

asn

lys

asp

glu

UGUUGCUGAUGG

CGUCGCCGACGG

AGUAGCAGAAGG

GGUGGCGGAGGG

cys

stoptrp

arg

ser

arg

gly

Firs

t B

ase

Third

Base

Second Base

Virtually all organisms share the same genetic code “unity of life”

mRNA AMINO ACID CHART

As each codon passes through ribosome, tRNA brings the proper amino acids to ribosome to build a polypeptide

Anticodon is used to base pair with mRNA codons

The polypeptide chain continues to grow until it reaches a “stop” codon on mRNA

Ribosome releases new polypeptide and mRNA, completing translation

TRANSLATION

Figure 10.8B

Startcodon

RNA

Transcribed strand

StopcodonTranslation

Transcription

DNA

Polypeptide

CODONS

Figure 10.16A

Normal hemoglobin DNA

mRNA

Normal hemoglobin

Glu

Mutant hemoglobin DNA

mRNA

Sickle-cell hemoglobin

Val

Mutations are changes in the DNA base sequence caused by errors in DNA replication or by

mutagens (chemical/physical agents) Point mutation involves change in one or

a few nucleotides

Types of mutations

Figure 10.16B

mRNA

NORMAL GENE

BASE SUBSTITUTION

BASE DELETION or INSERTION

Protein Met Lys Phe Gly Ala

Met Lys Phe Ser Ala

Met Lys Leu Ala His

Missing

*FrameshiftMutation (more serious)

FRAMESHIFT: Shifts entire sequence over, can result in defective protein

POINT Mutation- can produce defective protein

TAC GCC TGG AAA

AUG CGG ACC UUU

MET ARG THR PHE

Silent mutation (substitution) because there is more than one codon for each AA