DNA Replication
Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
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
Growth
Growth
Replication fork
DNA polymerase
New strand
Original strand DNA
polymerase
Nitrogenous bases
Replication fork
Original strand
New strand
Important Enzyme #2
DNA PolymerasePrincipal 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.
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’
What is ‘semi-conservative’ replication?
In the new DNA created, one strand is from the original, and one is a new one.
Semi = part ofConserve = save
Why is ‘semi-conservative’ important?
The DNA is copied EXACTLY generation to generation
RNAWhere is DNA stored? ______________________
What organelle makes proteins? ______________________
Where are proteins made? ______________________
Nucleus
Ribosomes
Cytoplasm
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: AGTCCTTTAGT
RNA: AGUCCUUUAGU
1. Ribosomal RNA (rRNA)
rRNA is found in ribosomes, and
creates the active site for protein
formation
III. Transcription
A. Transcription: Producing RNA by copying part of the DNA’s nucleotide sequence
RNADNA
RNApolymerase
Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
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
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. Proteins are long chains of amino acids.
B. 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
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
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
Methionine (START), Tyrosine, Arginine, Alanine, Phenylaline, STOP.
Serine, Methionine, Glutamic Acid, Valine, Isoleucine, Proline, STOP
Methionine, Cysteine, Proline, Glutamine, STOP, Lysine
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
2) Ribosome grabs mRNA. tRNA brings amino acids to the ribosome
Cytoplasm
mRNA Start codon
Ribosome
Methionine
Phenylalanine
tRNALysine (amino acid)
3) tRNA matches with complimentary mRNA.
Ribosome makes peptide bond between amino acids, and breaks the bond between tRNA and amino acid.
mRNARibosome
Translation direction
LysinetRNA
Peptide bond
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