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Biology B Guided NotesUnit 7: DNA
DNA StructureWhat is DNA?
__________________________________________________
The blueprint of life
o What is a blueprint?
In simple terms, DNA stores ________________________________ and contains the instructions for making __________________________ within the cell.
Double Helix
A double helix is like a __________________________________ or zipper
There are two sides that are connected in the middle
What is DNA made of?
The backbone of DNA is composed of alternating __________________________ and _________________________________________
The centers are composed of ______________________________________
A phosphate combined with a deoxyribose sugar connected to a nitrogen base is a nucleotide
o Held together by covalent bonds
Nucleotide = _________________________ + _________________________ + _______________________
Nucleotides
One strand of DNA is a ____________________ of nucleotides
o There are MILLIONS of nucleotides
Two nucleotides together make a ___________________
Nitrogenous Bases
There are 4 different NITROGENOUS BASES
o ______________________________
o ______________________________
o ______________________________
o ______________________________
Types of Nitrogenous Bases
o There are 2 types of bases
_______________________________: Single ringed base
_______________________________: Double ringed base
o Pyrimidines
______________________ and ______________________ are Pyrimidines
They both have a Y in their spelling
o Purines
______________________ and ______________________ are Purines
There are 2 n’s in each word; there are 2 rings in purines
Bases Pair Together
The four nitrogenous bases pair up with one another and make a chain.
Purines pair with Pyrimidines
o A pairs with T
o C pairs with G
o “Apple Tree, Chewing Gum”
This pairing is called _________________________ because each base complements one of the others.
The __________________ and _________________________ of DNA make up the _______________________ of the molecule.
Hydrogen Bonds
________________ bonds that hold the bases (A,T and C,G) together
A – T have _____ bonds ALWAYS!
C – G have _____ bonds ALWAYS!
o Chargaff’s Rule
DNA by Numbers
Each cell has about _________________ of DNA
The average human has __________________________ cells
The average person has enough DNA to go to the sun and back ___________________
Why Study DNA?
It is important to all life on Earth
Medical benefits such as cures for diseases
Better crops for food
Interactive “Build a DNA molecule” activity:
http://learn.genetics.utah.edu/content/basics/builddna/
DNA ReplicationWatson and Crick Model
• “It has not escaped our notice that the specific pairing we have *postulated immediately suggests a possible copying mechanism for the genetic material.”
• *Postulated: suggest or assume the existence, fact, or truth of (something) as a basis for reasoning, discussion, or belief
Replication definition
• To “replicate” means to ______________________________
• DNA Replication: _____________________________________________________________________________
Steps of Replication
• Occurs during ______________________ in the cell cycle
• Step 1: _________________________________________
• Step 2: _________________________________________
• Step 3: _________________________________________
Step one: Unzipping
• The DNA has to “unzip” so it can be _________________
• Done by an ______________
– ____________________________: An enzyme which splits the DNA strand at the beginning of DNA Replication.
– What kind of bonds is the helicase breaking? _____________________________
• What is an enzyme?
– A protein that ___________________ or ___________________________ molecules in our body
Step two: Adding Nucleotides
• Free Nucleotides: _____________________________________________________________________________
___________________________________________________________________________________________
• DNA Polymerase: _____________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
• Replication Fork: _____________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
Step three: New DNA molecules
• This is the purpose of Replication
• We end up with 2 __________________________ DNA molecules
Rate of Replication
• The DNA strand has an estimated __________________________ base pairs (A,C,T,G).
• The DNA strand is not replicated from start to finish. Rather, it is divided into 100 sequences about 100,000 bases long.
Errors
• Once in a while, the wrong _______________________ is added to the base pair
• ____________________________________ scans the strand to correct these mistakes
– We end up with ______________________ per 1 billion nucleotides
Transcription and TranslationProteins
_________ codes for ____________________ in our bodies
Our cells make proteins from our DNA
There are 2 steps to doing this: __________________________and __________________________
Step 1: Transcription
Making an ___________ molecule from DNA
RNA = _______________________________
How is RNA similar to DNA?
o RNA is a long chain of ___________________________
o RNA contains many of the same __________________________________________
How is RNA different from DNA?
o The sugar in RNA is _______________ (What is the sugar in DNA)? _______________________
o RNA is present ____________________ of the ____________________ in a cell (where is DNA located?)
___________________________
o RNA has only _________ strand (how many does DNA have?) ________
The bases in RNA are the same except for one. Instead of Thymine (T), RNA has ______________ (___).
o ___________________
o ___________________
o ___________________
o ___________________
A pairs with U
C pairs with G
Types of RNA
_____________ (Messenger RNA): A single strand of RNA nucleotides which is copied in a
process called transcription. The mRNA strand is used to bring the DNA code to the ribosome in
the cytoplasm.
_____________ (Transfer RNA): A segment of RNA nucleotides which carries amino acids to the
ribosomes. Each tRNA is composed of 3 parts: an amino acid, a sequence of RNA nucleotides,
and an anti-codon.
_____________ (Ribosomal RNA): Ribosomes are made up of rRNA. The role is to hold mRNA in
place. rRNA arranges the amino acids in the correct order. rRNA also folds the growing protein
strand at the ribosome.
o The RNA that we make from DNA is called ___________________________________, or mRNA
o We can make mRNA from DNA through ___________________________________________________
o Using a _________________________________________________, mRNA bases are joined together,
making an mRNA strand
Similar to DNA replication, transcription needs some help from enzymes in order to occur:
o ________________________________: unzips a section of the DNA strand and copies it
It uses one strand of DNA as a template from which _______________________
_____________________________________ to make a strand of RNA
A binds with U, G binds with C
This happens in the ___________________
The RNA polymerase unzips a segment of the DNA molecule that codes for a protein called a
___________
__________________: DON’T code for proteins, are spliced (cut) out
__________________: DO code for proteins (“ex-ons are ex-pressed”)
Once transcription is finished there is a complete strand of mRNA composed of codons.
Step 2: Translation
______________________ is the process of making ___________________from ______________.
Sections of mRNA code for certain _____________________________, which when linked together, form
proteins (polypeptides)
Codon
o mRNA is divided into sections with 3 bases each. Each section is called a CODON.
o Codon: ________________________________________________________________________
o For example, a strand of mRNA that looks like this: A U G C U G C A U
o Is read like this: __________ - _________ - _________
o Each codon codes for a specific _______________________________
o _________________________________ help us to determine which amino acid a certain codon codes
for.
o Amino acids are the _____________ no matter what organism they are found in.
AUG =
UCA =
CGC =
GCA =
UGA =
Translation occurs outside of the nucleus of a cell, with the help of _____________________________.
o REVIEW: What do ribosomes do? __________________________________________________
Ribosomes in the cell __________________________________________________ and recruit a molecule called
____________________________ (tRNA) to __________________________________ that codons code for.
Translation in More Detail
o tRNA contains an ________________________ and an amino acid
o Anti-codon: _____________________ of codon (ex. codon = AUG, anti-codon = _________)
o tRNA binds to the three letter codon from the mRNA strand
o The next tRNA enters and binds to the next codon
o The amino acids on top ___________________________________________
o _______________________________ = bonds between amino acids
Long chains of amino acids bonded together make a ____________________.
Ribosomal RNA (rRNA)
o Holds the mRNA in place
o Arranges the amino acids in the ______________________________
o ___________________________ to make it usable
MutationsGenetic Changes
A mutation is ________________________________________________________________________________
o Chromosomal mutations
o Frameshift mutations
o Point mutations
Only mutations in ______________________ can be transmitted to ___________________
o Potentially can produce __________________________
Chromosomal mutations
o ___________________________: Part of a chromosome is left out
o ___________________________: Part of a chromatid breaks off and attaches to its sister chromatid
o ___________________________: Part of a chromosome breaks off and reattaches backwards
o ___________________________: Part of one chromosome breaks off and is added to a different
chromosome.
Frameshift mutations
o A mutation in which a ____________________________ is ___________________________ or
___________________________________ DNA
THE DOG BIT THE CAT
THE DOB ITT HEC AT
Point mutations
o A change in a ________________________________________________ in DNA
THE DOG BIT THE CAT
THE DOG BIT THE CAR
Causes of mutations
Mutagens
o any agent which can cause a _____________________ in DNA
______________________________
______________________________
______________________________
______________________________
Asbestos
Benzene
Formaldehyde
Are mutations bad? Write your initial thoughts below:
__________________________________________________________________________________________________
__________________________________________________________________________________________________
Copy down next slide here:
__________________________________________________________________________________________________
__________________________________________________________________________________________________
Gene ExpressionGenes
Can be ___________________________ or __________________________
o Not always this simple (we’ll see some examples later)
Why do muscle cells differ from skin cells?
o Each cell reads the DNA code differently. Different _________________________ can produce different
______________________ in a protein. Thus, cells differ in _________ and _______________________.
Homozygous vs. Heterozygous
o Depending on whether an individual is homozygous or heterozygous for a trait, they can have the trait
even though it is not being __________________________.
Types of inheritance
Incomplete dominance
o The phenotype of the offspring is a __________ between the two genotypes of the parents.
o Example:
Codominant Alleles
o Causes the offspring to have __________ genotypes which are equally expressed.
o Example:
Polygenic Inheritance
o The trait is controlled by __________________________ genes.
o Examples:
Internal Factors
Eating Breakfast
Heart Attacks
Genes are turned _____ when they are needed and _______ when they are not needed
Environmental Influences
The environment around the organism can influence the genotype.
Examples: