Download DNA and Genes

DNA and Genes
Q: How do genes work? How do genes determine your characteristics? What
are genes made of?
Genes: Portions of DNA that contain the instructions for producing traits
**How does DNA produce traits?
 By producing proteins
 All body structures, skin, muscles and bones are made of
proteins
 Enzymes, also proteins, are critical for organ function and
chemical reactions
A. DNA (Deoxyribo Nucleic Acid)
 Polymer made of many nucleotides
1. Nucleotide: monomer for nucleic acids; 3 parts
 Sugar: deoxyribose
 Phosphate
 Nitrogen base (4 different)
a. Adenine (A)
b. Thymine (T)
c. Cytosine (C)
d. Guanine (G)
 Many of these nucleotides bond together between the nitrogen
bases and between a phosphate group of one nitrogen base and
the sugar of the next to form a double helix
 Adenine (A) and Thymine (T) always pair together; Cytosine (C)
and Guanine (G) always pair together
 Double Helix: twisted ladder, shape of DNA
 Backbone: phosphate and sugar (deoxyribose)
 ½ rung/step: Nitrogen base (ATGC)
 Weak H bonds hold the two halves of the ladder together
From DNA to Proteins
Background Info:
1. DNA is located in the nucleus and stays in the nucleus
2. Must make a partial copy of itself that will leave the nucleus and go the
ribosome (site of protein production)
3. Ribosome reads the information and constructs the proteins according
to the code
A. RNA (Ribo Nucleic Acid)
 Polymer made of many nucleotides
 RNA Nucleotides: 3 parts
1. sugar: Ribose
2. Phosphate
3. Nitrogen Base:
a. Adenine (A)
b. Uracil (U)
c. Cytosine (C)
d. Guanine (G)
 Structure of RNA: single stranded
1. 3 Types of RNA
a. mRNA (messenger RNA)
 carries the information/carries the message from the DNA
(located in the nucleus) to the ribosomes
 contains Codons: 3 nucleotides in a row that represent
an amino acid
 Ex. UUU = phenylalanine
CUG = leucine
ACG = threonine
b. rRNA (ribosomal RNA)
 is the actual ribosome (ribosomes are made of nucleic
acids)
 reads the mRNA and uses it to assemble proteins
c. tRNA (transfer RNA)
 transports amino acids within the cytoplasm to the
ribosome to assemble proteins in the order according to
mRNA
 Anticodon: 3 nucleotides on the tRNA that match up
with the condon on mRNA and drop off/release the
amino acid in the correct position; ensures that amino
acid is the correct one
B. DNA Replication
When does DNA replicate?
 Mitosis and Meiosis: making new cells
How does DNA replicate/copy itself?
1. Untwists: The double helix becomes untwisted
2. Unzips: enzymes break the hydrogen bonds between
nitrogen bases; leaves nitrogen bases unpaired on both
sides of the ladder
3. Fill in the empty spaces: complementary nucleotides (DNA)
(AT/CG) that are floating around in the cytoplasm pair up
forming 2 new strands of DNA
C. DNA Transcription
 The process in which DNA is used to write out a portion of the
code in the form of mRNA
 DNA is the template (serves as a pattern) for making mRNA
Steps: similar to DNA replication
1. Untwist: double helix (DNA) untwists
2. Unzips: enzymes break the hydrogen bonds between
complementary nucleotides causing the 2 strands of DNA to
separate
3. Fill in the spaces: Complementary RNA nucleotides bind to
one of the single DNA strands and then releases from the
DNA, leaving the nucleus, and heading to the ribosome to
make the protein
4. DNA twists back up again
DNA 1st Strand
A C G T T C A C G T A
mRNA
U G C A A G U G C A U
DNA 2nd Strand
T G C A A G T G C A T
***Note: (U) uracil pairs up with (A) adenine, not (T) thymine
 If (T) thymine is on DNA the complementary base is still (A)
adenine
***Hint: when using the first strand of DNA to make mRNA, copy the
second strand of DNA in order, but replace (T) thymine with (U) uracil
D. RNA Translation (Protein Synthesis)
 Converting the code in mRNA to amino acids that make up
proteins
 It’s the sequence/order of nitrogen bases on DNA that
determine the protein synthesized
 Translation takes place at the ribosome
 Each codon on the mRNA represents an amino acid
 The tRNA brings the amino acid to the ribosome and
temporarily binds its anticondon with the mRNA condon to
ensure the amino acid belongs in that position
mRNA Codon
A U C
1.
2.
3.
G G A
Codon (mRNA)
A U G
G G A
U U A
U U A
C A U
Anticodon (tRNA)
U A C
C C U
A A U
Use a codon chart to look up the amino acids
Amino Acid
Methionine (start)
Glycine
Leucine
Q: If all cells contain the same genetic information (46 chromosomes) why do
they have different structures and functions?
A: Only certain parts of the DNA become activated within those cells
46 chromosomes
genes
codons/amino acids
proteins
Cookbook
recipe
ingredients list
product
E. Genetic Changes
1. Mutations: any change in the DNA sequence
 Remember the sequence of nucleotides determines the
necessary proteins
 If the nucleotide sequence changes due to a mutation
the incorrect protein will be made
 Causes of mutation: radiation, chemicals, carcinogens,
pollutants, spontaneous
a. Mutations in Gametes:
 If the nucleotide sequence changes in the DNA of an
egg or sperm cell that change will be passed on to
future generations of offspring
b. Mutations in Body Cells:
 If the nucleotide sequence changes in the DNA of a
body cell it will not be passed on to the offspring
 These mutations may impair the function of that
particular cell
2. Types of Mutations in DNA
a. Point Mutation (Substitution): one nitrogen base
changes = only one amino acid changes
b. Frameshift Mutation: the addition or deletion of a
nitrogen base
 Nucleotides shift over and all amino acids are
changed after the deletion or addition
c. Chromosomal Mutations: entire portions of DNA are
deleted, inserted, inversed (backwards), translocated