CHAPTER 10

NUCLEIC ACIDS & PROTEIN SYNTHESIS

STRUCTURE OF DNA

• MADE UP OF REPEATED UNITS CALLED NUCLEOTIDES

• NUCLEOTIDES HAVE 3 PARTS:– 5 carbon sugar (deoxyribose)– Phosphate group

– Nitrogen base

• 4 NITROGEN BASES IN DNA– PURINES – made of 2 rings of carbon &

nitrogen; adenine & guanine– PYRIMIDINES – made of 1 ring of carbon &

nitrogen; thymine & cytosine

PURINES

DOUBLE HELIX

• James Watson & Francis Crick• DNA is composed of 2 nucleotide chains

wrapped around each other (spiral staircase)

• Alternating sugar & phosphate molecules make up the backbone of the DNA (sides)

• Nitrogen base pairs form the stairs of the ladder

COMPLEMENTARY BASE PAIRS

• ADENINE TO THYMINE

• CYTOSINE TO GUANINE

• NITROGEN BASES ARE JOINED BY HYDROGEN BONDS

DNA REPLICATION( PROCESS OF COPYING DNA)

• Begins simultaneously along different points

• Results in 2 new exact copies of the original DNA

• Occurs in the nucleus during interphase

1. Enzyme called DNA helicase breaks the hydrogen bonds between the nitrogen bases separating the double helix

-Point where the chains separate is called the replication fork

2. New nucleotides will bond to the broken chains with the help of the enzyme DNA polymerase(A to T and C to G)

- Mistakes in the base pairing results in a mutation; special enzymes are present to help repair mistakes

DNA REPLICATION ANIMATION

• http://www.lewport.wnyric.org/jwanamaker/animations/DNA%20Replication%20-%20long%20.html

RNA

• Also made of repeated units called nucleotides– Ribose sugar

– Phosphate group– Nitrogen bases – contains uracil in place of

thymine

– Single strand

TYPES OF RNA

• Messenger RNA – mRNA – carries the message in DNA out of the nucleus

• Transfer RNA – tRNA – transfers amino acids to the ribosome

• Ribosomal RNA – rRNA – most abundant; makes up ribosomes

TRANSCRIPTION

• Process by which the information in DNA is copied to RNA

1. Enzyme called RNA polymerase joins to DNA at the promoter site causing the strands of DNA to separate

2. Free RNA nucleotides bond to the open DNA strands by pairing A to U and C to G

3. Continues until a termination signal is reached

4. RNA is released and the DNA strands rejoin

TRANSCRIPTION ANIMATIONS

• http://www.ncc.gmu.edu/dna/mRNAanim.htm

• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

TRANSLATION

• Proteins synthesis – making of proteins• The directions for assembling a protein are

hidden in the DNA• mRNA copies the message & takes it to

the ribosome• The ribosome decodes the mRNA and

assembles the amino acids in the correct order

1. mRNA carries the message to the ribosome

- 3 mRNA nucleotides that code for a specific amino acid are called codons

2. tRNA transports the amino acids to the ribosome

- Clover shaped with an amino acid on top & anticodon on bottom

3. Codons of mRNA match to the anticodons of tRNA

4. After amino acids are in place they join with a peptide bond to form proteins.

TRANSLATION ANIMATIONS

• http://nobelprize.org/medicine/educational/dna/b/translation/translation_ani.html

• http://www.ncc.gmu.edu/dna/ANIMPROT.htm