Honors Biology
Powerpoint #2 – Chapter 12

Warm Up: Base Pairing
1.
A C C T G A
2
.
G C T A
G A G

What is the DNA ‘backbone’ made of?


Sugar-phosphate backbone
Nucleotide
DNA Replication
Hydrogen bonds
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

What is DNA replication?
Making a copy of DNA
Why is DNA replication important for cells and multicellular organisms?
Replication allows cells to divide
Forming cells that are genetically identical to the original

When does DNA Replication occur?
After the cell grows big enough to divide, during interphase, the
“S” phase

DNA Replication
New strand
Original strand
DNA polymerase
Replication fork
DNA polymerase
Growth
Growth
Replication fork
Nitrogenous bases
New strand
Original strand

Important Enzyme #1
Helicase

Unwinds DNA at the replication fork.

Important Enzyme #2
DNA Polymerase

Principal enzyme in DNA replication; adds nucleotides to growing strand of DNA and proofreads new strand of DNA

Steps in DNA Replication
1. Helicase enzyme breaks the hydrogen bonds between base pairs. This unzips the double helix at a position called the replication fork.
2. There is an abundant supply of nucleotides in the nucleus for the formation of the new polynucleotides.
3. Nucleotides base pair to the bases in the original strands with hydrogen bonds.
4. DNA polymerase joins together the nucleotides together with strong covalent bonds to form a new complementary polynucleotide strand.
5. The double strand reforms a double helix.
6. Two copies of the DNA molecule form behind the replication fork. These are the new daughter chromosomes.

Drawings of the steps in DNA
Replication
DNA
Polymerase
Helicase

Some Important DNA Facts

A strand of DNA has 2 ends, the 5’ (5-prime) and 3’ (3-prime) ends.

DNA is ALWAYS copied from 5’ to 3’

Some Important DNA Facts

There are multiple ‘bubbles’ of DNA replicated at the same time

What is ‘semi-conservative’ replication?

In the new DNA created, one strand is from the original, and one is a new one.
Semi = part of
Conserve = save
Why is ‘semi-conservative’ important?

The DNA is copied EXACTLY generation to generation

RNA

Where is DNA stored?

What organelle makes proteins?

Where are proteins made?

What problem might this pose?

DNA can not take directions for making proteins to the ribosomes.

How does RNA solve this problem?

RNA is a disposable copy of DNA that can leave the nucleus

B. RNA’s structure is very similar to the structure of
DNA except for 3 major differences:
1.
RNA has ribose sugar instead of deoxyribose
Nitrogen Base

2. RNA is single-stranded
3. RNA has uracil (U) instead of thymine (T)
DNA: AG T CC TTT AG T
RNA: AG U CC UUU AG U

There are three main types of RNA:

1. Ribosomal RNA (rRNA) rRNA is found in ribosomes, and creates the active site for protein formation

2. Transfer RNA (tRNA) tRNA contains the anticodon, and brings amino acids to create proteins

3. Messenger RNA (mRNA) mRNA provides the template for making proteins

III. Transcription
A.
Transcription: Producing RNA by copying part of the DNA’s nucleotide sequence
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA polymerase
DNA
RNA

B.
Describe the process of transcription using drawings.
1. RNA Polymerase rips open the DNA double helix
2. RNA polymerase grabs bases and lines them up with the original DNA strand
3. Half of the DNA is copied into a strand of mRNA, then the
DNA strand closes, hydrogen bonds reform

Transcription

C. How does RNA polymerase know where to start?
Starts when it finds a “promoter”
(specific base sequence)
Found near the beginning of a gene sequence

D. Describe the process of RNA editing



RNA editing is a process that occurs in the nucleus.
It removes introns “intervening sequences” and leaves mRNA with only the exons “expressed sequences.”
After editing a cap and tail are attached and the mRNA is ready to enter into the cytoplasm.

IV. Translation
A.
B.


Proteins are long chains of amino acids.
Codon: 3 consecutive nucleotides that
“code” for a specific amino acid.

What is the universal “start” codon:
AUG

What are the three “stop” codons?
UGA, UAA, UAG

The Genetic Code

The Genetic Code

C. Use the genetic code below to translate the following mRNA sequences:
1.
mRNA:
A U G U A U C G G G C A U U U U A A
2.
mRNA:
U C C A U G G A A G U G A U U C C A U A A
3.
mRNA:
C C A U G U G U C C C C A A U G A A A A

C. Use the genetic code below to translate the following mRNA sequences:
1.
mRNA:
A U G U A U C G G G C A U U U U A A
Methionine (START), Tyrosine , Arginine , Alanine , Phenylaline , STOP .
2.
mRNA:
U C C A U G G A A G U G A U U C C A U A A
Serine , Methionine , Glutamic Acid , Valine , Isoleucine , Proline , STOP
3.
mRNA:
C C A U G U G U C C C C A A U G A A A A
Methionine , Cysteine , Proline , Glutamine , STOP , Lysine

D. Translation:
The decoding of
RNA into a polypeptide chain (protein)

E.
The Central Dogma of
Biology is:
DNA  RNA  protein
Where does the first step take place? Nucleus
Where does the second step take place?
Cytoplasm

F. What is the job of tRNA during translation?
Bringing amino acids to the ribosomes and match them up with the correct base on mRNA.
What is an anticodon? The three bases on a tRNA that match with the mRNA codons.
G. What is the role of the ribosome during translation? It is the site of protein assembly

H. 1) mRNA is transcribed in the nucleus then travels to the cytoplasm
Cytoplasm
Nucleus mRNA

2) Ribosome grabs mRNA . tRNA brings amino acids to the ribosome
Methionine
Phenylalanine tRNA
Lysine (amino acid)
Ribosome mRNA
Start codon
Cytoplasm

3) tRNA matches with complimentary mRNA.
Ribosome makes peptide bond between amino acids, and breaks the bond between tRNA and amino acid.
Lysine
Peptide bond tRNA mRNA
Ribosome
Translation direction

4) Peptide chain continues to grow until ribosome reaches a stop codon
Protein is complete.
Growing polypeptide chain
Ribosome tRNA
Stop codon mRNA