Bell WorkWhat type of bond holds

nucleotide bases together and why is it important?

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

Cell Cycle of Eukaryotes

Prophase Metaphase

Anaphase

Telophase &

Cytokinesis

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 strandDNA 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

Bell Work

What is a mutation? Are they harmful or beneficial to you?

Explain.

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 organismsCan 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- Mutations1. Frame Shift Mutations

Deletion Frameshift Mutation- A base is accidentally left out Insertion Frameshift Mutation- A base is accidentally inserted

2. 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- Mutations1. 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- Mutations2. 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- Mutations3. 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: TCG TAG AAG TAC

Replicated strand: AA C ATC TTC TTG

________________

Let’s Do Lunch!

Instructions: You will be given 2 minutes to fill in your lunch appointments (note:

you can not repeat a luncheon appointment).

Once you have your dates set, you will be given 5-7 minutes to “consume” the material given and “regurgitate” your

answers!