Download DNA Function

Important Vocabulary

Genes- segment of DNA; structural/functional
unit of heredity; each contains genetic info. that
tells the cell to make specific protein

Chromosome- a long strand of tightly bound
DNA

DNA- double stranded, helical nucleic acid
molecule that determines the inherited
structure of cell’s proteins

Replication- process of copying DNA prior to
cell division (mitosis/meiosis)
DNA Replication
Purpose: To create
an exact copy of
DNA for new cell
 Late in interphase
(S Phase)
 DNA separates into
2 strands; each
strand serves as a
template for a new
strand
 Cell goes through
mitosis or meiosis

Prophase
A Closer Look…
Each of your cells has 46 DNA
molecules in its nucleus (one long
double helical molecule per
chromosome)
 We have 6 billion base pairs that can be
copied in a couple of hours

Where Replication Begins:
Begins at sites called the origins of
replication (there are many)
 Proteins initiate DNA replication

 The two strands separate at the replication
fork, and create a replication bubble

DNA replication proceeds in both
directions until copying is finished!
First Step in replication
Helicase- unzips the molecule of DNA



Breaks H bonds between base pairs
Creates 2 DNA templates
2nd Step in Replication

Polymerase- joins individual nucleotides
producing a new DNA strand; it also proofreads
each new strand
 DNA strands are antiparallel (oriented in opposite
directions)
 DNA strand elongates in a 5’-3’ direction (5’ leads w/
phosphate & 3’ leads w/ sugar)
○ The strand being built 5’-3’, has Polymerase continuously
adding base pairs leading strand
○ The strand that is built 3’-5’, has Polymerase
synthesizing in segments  lagging strand (Okazaki
fragments)
 DNA ligase eventually joins the fragments
C
3. Telomerase- adds short repeated
DNA sequences to the telomeres

Telomeres- DNA at
the chromosome
tips; difficult to
replicate (especially
lagging strands)
 Helps prevent genes
from being lost or
damaged in
replication
Mutations
What
is a mutation?
Mistake in copying DNA
 Heritable changes in genetic info

Harmful or Beneficial?

Harmful – change protein structure or gene
activity dramatically
 Can disrupt normal biological activities  genetic
disorders (ie. Genetic disorders)

Beneficial- proteins are altered in a way that
causes positive/useful effects to organisms
 Can be useful to organisms in different or changing
environments

Silent- an alteration in a DNA sequence that
does not result in a change in protein
Problems with Replication- Mutations
Frame Shift Mutations
1.


2.

Deletion Frameshift Mutation- A base is accidentally left out
Insertion Frameshift Mutation- A base is accidentally inserted
Point Mutation/Substitution- The wrong base is
substituted
Environmental agents or radiation may also change
the base sequence- mutagens
Recall how DNA is read…
A sequence of DNA are like letters of a coded
message telling our cells what protein to make.
 DNA is decoded in sets of 3 (codon)
 Ie. THE KID ATE AND WAS FAT
 Ie. ATG CGG ATT ACG

Problems with Replication- Mutations
1. Deletion Frameshift Mutation- A base is accidentally
left out
Example:
the big dog bit the cat but not the boy
If a single base was deleted such as “o”
in “dog”. The sentence would now read:
the big dgb itt hec atb utn ott heb oy
Deletion Frameshift
DNA strand:
ACG TAG GTC TCG AAT
Replicated strand:
TGC ACC AGA GCT TA
Problems with Replication- Mutations
2. Insertion Frameshift Mutation- A base is accidentally
inserted
Example:
the big dog bit the cat but not the boy
If a single extra base was inserted such as “r”
in “dog”, after the “o”. The sentence would now
read:
the big dor gbi tth eca tbu tno tth ebo y
Insertion Frameshift
DNA strand:
ACG TAG GTC TCG AAT
Replicated strand:
TGC AAT CCA GAG CTT A
Problems with Replication- Mutations
3. Point Mutation/Substitution- The wrong base is
substituted
Example:
the big dog bit the cat but not the boy
If the "d" in dog got replaced by a "p". The
sentence would now read:
the big pog bit the cat but not the boy
Point Mutation
DNA strand:
ACG TAG GTC TCG AAT
Replicated strand:
TCC ATC CAG AGC TTA
Identify the following mutation:
1.
Original strand:
TCG GTA ATC GAT
Replicated strand: AGC ATT AGC TA
________________
2.
Original strand:
Replicated strand:
TCG TAG AAG TAC
AA C ATC TTC TTG
________________