Transcript DNA and Genes student

1. What are the 3 components of this DNA
nucleotide?
2. What is the function of DNA in the cell?
Genetics
DNA and Genes
DNA: The Molecule of Heredity
Contributors to DNA Discovery
• 1943 Oswald Avery: DNA carries genetic information
• 1952 Franklin took the first picture of DNA using X-RAY
Contributors to DNA Discovery
1953 - Watson & Crick proposed the
structure of DNA
1962 - Nobel Prize to Watson and
Crick
• “FATHERS OF DNA”
Contributors to DNA Discovery
• So? Was it that clear cut??
• What event occurred allowing Watson and Crick to discover the DNA
structure?
What is DNA?
• Deoxyribonucleic Acid
– determines an organism’s traits
– ultimately determines the structure of
proteins.
• body is made up of proteins
• body’s functions depend on proteins
called enzymes.
The Structure of DNA
• DNA is a polymer made of nucleotides.
• Nucleotides have three parts:
– simple sugar
– phosphate group
– nitrogenous base.
• composed of one atom
of phosphorus
surrounded by four
oxygen atoms.
carbon ring structure
that contains one or
more atoms of
nitrogen.
Nitrogenous
base
Phosphate
group
Sugar (deoxyribose)
• Deoxyribose is the simple
sugar in DNA
The structure of nucleotides
• In DNA, there are four possible nitrogenous
bases: adenine (A), guanine (G), cytosine (C),
and thymine (T).
*always pair
Adenine (A)
Thymine (T)
* always pair
Cytosine (C)
Guanine (G)
The structure of nucleotides
• Thus, in DNA there are four possible
nucleotides, each containing one of these
four bases.
• Nucleotides join together to form long
chains.
– Formed by covalent bonds
– These chains are known as the Double
Helix
The structure of nucleotides ****
The importance of nucleotide sequences
Chromosome
The sequence of nucleotides
in each gene contains
information for assembling
the string of amino acids that
make up a single protein.
Genes and Proteins
• Proteins make up the structure of an organism AND control all of the
organism’s chemical reactions to keep it alive
DNA and Cell Division
DNA to Protiens
• Remember…DNA ultimately determines structure of proteins.
• These proteins are what makes “us” and enables “us” to function…..
• So how do we get these specific proteins???
Replication of DNA
• Before a cell can divide by mitosis or
meiosis, it must first make a copy of its
chromosomes.( Interphase)
• The DNA in the chromosomes is copied in
a process called DNA replication.
• Without DNA replication, new cells would
have only half the DNA of their parents.
Cells Start Here: Transcription
• Transcription results in the formation of one
single-stranded RNA molecule.
– takes place in the nucleus
• mRNA, which is seen in here, takes the
instructions from the nucleus to the
cytoplasm.
What is RNA?
• RNA is single stranded
•The sugar is ribose
•Rather than thymine,
RNA contains a similar
base called uracil (U).
Uracil
Hydrogen bonds
Adenine
Why RNA???
• DNA provides
workers with the
instructions for
making the
proteins, and
workers build the
proteins.
• The workers for
protein synthesis
are RNA
molecules.
Back to Copying DNA….
• Once mRNA is in the cytoplasm… Ribosomal RNA (rRNA) binds to the
mRNA and uses the instructions to assemble the amino acids in the
correct order.
• This starts Translation
Translation: From mRNA to Protein
• Translation is the process of converting the
information in a sequence of nitrogenous
bases in mRNA into a sequence of amino
acids in protein.
• Translation takes place at the ribosomes in
the cytoplasm.
The role of transfer RNA
Amino
acid
• Each tRNA
molecule attaches
to only one type
of amino acid.
Chain of RNA
nucleotides
• An anticodon is a
sequence of three
bases found on
tRNA.
Transfer RNA
molecule
Anticondon
The role of transfer RNA
Ribosome
mRNA codon
The role of transfer RNA
• The first codon on mRNA is AUG, which
codes for the amino acid methionine.
• AUG signals the start of protein synthesis.
• Then the ribosome slides along the mRNA
to the next codon.
The role of transfer RNA
Methionine
tRNA
anticodon
The role of transfer RNA
• A new tRNA molecule carrying an amino acid
pairs with the second mRNA codon.
Alanine
The role of transfer RNA
• The amino acids are joined when a peptide
bond is formed between them.
Methionine
Alanine
Peptide
bond
The role of transfer RNA
• A chain of amino acids is formed until the
stop codon is reached on the mRNA strand.
Stop
codon
The Genetic Code
The Messenger RNA Genetic Code
First
Letter
U
U
Phenylalanine (UUU)
A
G
Third
Letter
G
Serine (UCU)
Tyrosine (UAU)
Cysteine (UGU)
Serine (UCC)
Tyrosine (UAC)
Cysteine (UGC)
Leucine (UUA)
Leucine (UUG)
Serine (UCA)
Stop (UAA)
Stop (UGA)
Serine (UCG)
Stop (UAG)
Tryptophan (UGG)
Leucine (CUU)
Proline (CCU)
Histadine (CAU)
Arginine (CGU)
Leucine (CUC)
Proline (CCC)
Histadine (CAC)
Arginine (CGC)
Leucine (CUA)
Proline (CCA)
Glutamine (CAA)
Arginine (CGA)
Leucine (CUG)
Isoleucine (AUU)
Proline (CCG)
Glutamine (CAG)
Arginine (CGG)
Threonine (ACU)
Asparagine (AAU)
Serine (AGU)
Isoleucine (AUC)
Threonine (ACC)
Asparagine (AAC)
Serine (AGC)
Isoleucine (AUA)
Methionine;
Start (AUG)
Threonine (ACA)
Lysine (AAA)
Threonine (ACG)
Lysine (AAG)
Arginine (AGA)
Arginine (AGG)
Valine (GUU)
Alanine (GCU)
Aspartate (GAU)
Glycine (GGU)
Valine (GUC)
Alanine (GCC)
Aspartate (GAC)
Glycine (GGC)
Valine (GUA)
Valine (GUG)
Alanine (GCA)
Alanine (GCG)
Glutamate (GAA)
Glutamate (GAG)
Glycine (GGA)
Glycine (GGG)
Phenylalanine (UUC)
C
C
Second Letter
A
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
DNAi
•Triplet code
•Translation
http://www.pbs.org/wgbh/nova/body/rnai.html
1. Why is this exact base sequence important?
2. What may be the result of “wrong” base
sequencing?
Mutations
• Organisms have evolved many ways to
protect their DNA from changes.
• In spite of these mechanisms, however,
changes in the DNA occasionally do occur.
• A mutation is any change in a DNA sequence.
• Mutations can be caused by errors in
replication, transcription, cell division,
or by external agents.
Mutations in reproductive cells
• Mutations can occur in the reproductive
cells.
– This then becomes part of the genetic
makeup of the offspring.
– If the change makes a protein
nonfunctional, the embryo may not
survive.
Mutations in body cells
• What happens if powerful radiation, such as
gamma radiation, hits the DNA of a
nonreproductive cell, a cell of the body such as
in skin, muscle, or bone?
• If the body cell’s DNA is changed, this mutation
would not be passed on to offspring.
• The mutation may cause problems for the
individual.
The effects of point mutations
• A point mutation is a change in a single
base pair in DNA.
• A change in a single nitrogenous base can
change the entire structure of a protein because
a change in a single amino acid can affect the
shape of the protein.
The effects of point mutations
mRNA
Normal
Protein
Stop
Replace G with A
mRNA
Point
mutation Protein
Stop
Frameshift mutations
• A frameshift mutation is a mutation in which a
single base is added or deleted from DNA.
• A frameshift mutation shifts the reading of
codons by one base.
• This mutation would cause nearly every
amino acid in the protein after the
deletion to be changed.
Frameshift mutations
Deletion of U
Frameshift
mutation
mRNA
Protein
Chromosomal Alterations
• Chromosomal mutations are structural changes
in chromosomes.
• When a part of a chromosome is left out, a
deletion occurs
•
A B C D E
F G H
A B C E
Deletion
F G H
Chromosomal Alterations
• When part of a chromatid breaks off and
attaches to its sister chromatid, an insertion
occurs.
• The result is a duplication of genes on the
same chromosome.
A B C D E
F G H
A B C B C D E
Insertion
F G H
Chromosomal Alterations
• When part of a chromosome breaks off and
reattaches backwards, an inversion occurs.
A B C D E F G H
A D C B E FGH
Inversion
Chromosomal Alterations
• When part of one chromosome breaks off
and is added to a different chromosome, a
translocation occurs.
AB C D E F GH
WX Y Z
W X AB C DE F GH
Translocation
Y
Z
Causes of Mutations
• A mutagen is any agent that can cause a
change in DNA.
• Mutagens include radiation, chemicals, and
even high temperatures.
• Forms of radiation, such as X rays, cosmic
rays, ultraviolet light, and nuclear radiation,
are dangerous mutagens because the energy
they contain can damage or break apart
DNA.
Causes of Mutations
• The breaking and reforming of a doublestranded DNA molecule can result in deletions.
• Chemical mutagens include dioxins, asbestos,
benzene, and formaldehyde, substances that
are commonly found in buildings and in the
environment.
• Chemical mutagens usually cause
substitution mutations.
Repairing DNA
• Repair mechanisms that fix mutations in cells
have evolved.
• Enzymes proofread the DNA and replace
incorrect nucleotides with correct nucleotides.
• These repair mechanisms work extremely well,
but they are not perfect.
• The greater the exposure to a mutagen such as
UV light, the more likely is the chance that a
mistake will not be corrected.