Download DNA Replication

Things to Discuss:
• DNA replication: DNA to DNA
How? When? Why?
• Structure of RNA compared to DNA
• Transcription: DNA to RNA
Exons vs. Introns  what DNA is important?
• Translation: RNA to protein
Reading the coded message
• Mutations: How can the message go wrong?
• Expression: Genes can be “on” or “off.”
What signals that?
DNA Replication
BIO 392
Ch. 12-2
G
C
A
T
What is the monomer of this polymer?
DNA: Deoxyribonucleic acid
Polymer: nucleic acid
Monomer: nucleotide – 3 parts
phosphate
group
nitrogencontaining
base
deoxyribose
(sugar)
hydrogen bond
covalent bond
Recall the 4 bases of DNA
Why Replicate?
• Remember, you are made of trillions
of cells. But you started as 1 CELL,
with 1 copy of DNA!
DNA Replication: When
• The Instructions for your growth is in the DNA
• As a multicellular organism, you need
instructions in every cell.
• Before MITOSIS and MEIOSIS, your DNA copies
itself so that each new cell has an exact copy:
When? During…
INTERPHASE
DNA Replication: Where
• Where is the DNA located?
• Eukaryotes  nucleus
– Recall: DNA is linear, in the form of chromosomes
• Prokaryotes  cytoplasm
– DNA is circular
Starting DNA Replication: How
• Which base pair bond will be the easiest to break?
• A-T
• 2 H+ bonds, instead of 3 like C-G
• Areas with lots A-T pairs are called
replication origins
Replication Origins
• AT rich sites
• Prokaryotic DNA only has 1 replication origin
• Eukaryotic DNA is too big to reproduce in a
reasonable amount of time with 1 replication
origins
– uses multiple (hundreds) of replication origins
What opens replication origins?
• DNA opened by initiator
proteins
• DNA is unzipped by HELICASE.
• Helicase unzips DNA at the
“speed of a jet plane”
• Creates 2 replication forks
moving in opposite directions.
How Does DNA Replicate Accurately?
• Each strand of the newly opened double
stranded DNA acts as a template for making a
new double strand of DNA
• Each half (strand) of the original DNA is known
as a parent strand
• The new, complementary strand of DNA that
matches is called the daughter strand
SEMI-CONSERVATIVE REPLICATION
• ½ old DNA coding for ½ new DNA is known as SEMICONSERVATIVE REPLICATION
• During replication: each old double strand will:
1. Unzip into 2 single strands, which will:
2. Code for a complementary strand (A-T; G-C)
3. Which will attach with H+ bonds to form:
4. 2 new double strands with:
5. 1 new single strand and 1 old single strand each
Semi-Conservative Replication
Adding Complementary Bases
• Need enzyme =
DNA Polymerase
• Add bases onto 3’ end
2 jobs:
• Add bases
complementary to
template strand
• “Proofread” and correct
new double strand DNA
DNA Replication
• Prokaryote DNA polymerase adds 1000
nucleotides/sec
• Eukaryote DNA polymerase adds 100
nucleotides/sec.
FYI: Sun directly damages DNA by bonding
thymine bases side-by-side. This can create
confusion during replication. Polymerase has
difficulty reading this abnormality and might
skip it, match just one A or interpret as a big
purine.
www.johnkyrk.com
mRNA
RNA: Ribonucleic
Acid
rRNA
Differences between RNA and DNA
DNA
Deoxyribonucleic Acid
RNA
Ribonucleic Acid
•
•
•
•
•
•
•
•
•
•
•
•
Double stranded
Deoxyribose sugar
Thymine (A,C,T,G)
DNA polymerase
“Master Copy”
1 major form*
Single stranded
Ribose sugar
Uracil (A,C,U,G)
RNA polymerase
“Working Copy”
3 major forms
Messenger RNA: mRNA
• Single-stranded, linear RNA
• Carries information from DNA to ribosomes
Ribosomal RNA: rRNA
• Helps form the structure of ribosomes, along
with proteins
• Long coils of RNA
Transfer RNA: tRNA
• Short coils of RNA found in cytoplasm
• Matches amino acids to mRNA
Can you identify the 3 RNAs?
Section 12-3
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
Recap…
• What are the 3 structural differences between
RNA and DNA?
• What are the 3 types of RNA?
• What enzyme unzips the DNA helix?
• What enzyme reads and matches nucleotides
to the parent DNA strand?
• When does DNA replication happen?
• What is a replication origin?