bell work what type of bond holds nucleotide bases together and why is it important?
TRANSCRIPT
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
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
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
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
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
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
Identify the following mutation:
1. Original strand: TCG GTA ATC GAT
Replicated strand: AGC ATT AGC TA
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2. Original strand: TCG TAG AAG TAC
Replicated strand: AA C ATC TTC TTG
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