Download Genetics and Protein Synthesis

GENETICS AND
PROTEIN SYNTHESIS
EOC Crash Course
Item 1: Describe the basic structure of the
nucleic acids – DNA and RNA
■ Nucleic acids are composed of
nucleotides
■ Nitrogen base + sugar + phosphate
Item 2: State the 3 structural
differences between DNA and RNA
1. RNA contains ribose; DNA contains
deoxyribose
2. DNA contains adenine (A), thymine (T),
guanine (G), and cytosine (C) ; RNA
contains A, G, C, and uracil (U)
3. DNA is double stranded (double helix);
RNA is single stranded (single helix)
Item 3: Summarize the relationship
between DNA, genes, and chromosomes
■ Chromosome – structure in the nucleus consisting of
one long thread of DNA that is tightly coiled around
special proteins called histones
■ DNA – molecule composed of nucleotides, providing the
blueprint for the making of proteins
■ Gene – segment of DNA with the genetic code for
making one protein
■ Chromosomes are made of DNA (and protein), in which
small segments code for the amino acid sequence of a
protein
■
Item 4: Summarize DNA Replication
1. Enzyme helicase unwinds DNA
2. Enzymes breaks hydrogen bonds holding pairs
bases together
3. Another enzyme bonds new DNA nucleotides to
each strand
4. Each identical DNA molecule has ½ the original
strand and ½ of a new strand
a. This is called the semi-conservative model
Item 5: Summarize Protein Synthesis
■ Consists of two steps:
– Transcription: DNA to mRNA
– Translation: mRNA to
polypeptide (protein)
Transcription
■ The two complementary strands of DNA separate by
breaking the hydrogen bonds between paired bases
■ An enzyme bonds RNA nucleotides to one DNA strand
■ C bonds to G and A (on DNA) bonds to U (on RNA)
Translation
■ Translation begins with mRNA attaching to a
ribosome
■ The first codon on mRNA is read (usually
AUG) and the tRNA with the codon’s
corresponding anticodon brings an amino
acid to the ribosome
■ A second codon is read and a second tRNA,
also carrying the corresponding amino acid,
attaches to the codon
■ The two amino acids bond together
■ The first tRNA breaks away from the
mRNA and the mRNA slides down to read
the next codon
■ This continues until one of the stop
codons is reached
■ The long chain of amino acids is a
polypeptide
Amino acids bond by making peptide
bonds
The Genetic Code
Item 6: Summarize steps of meiosis
■ Meiosis is very similar to mitosis, except
– in meiosis, the daughter cells divide twice
instead of once
– crossing over occurs during prophase I
(mixes up genes)
– chromatids don’t separate until anaphase II
– all 4 daughter cells are genetically different,
cells are haploid (1 chromosome per pair)
Stages of Meiosis: Meiosis I
■ Prophase I: The chromosomes condense, and the nuclear
envelope breaks down. crossing-over occurs
■ Metaphase I: Pairs of homologous chromosomes move to
the equator of the cell.
■ Anaphase I: Homologous chromosomes move to the
opposite poles of the cell
■ Telophase I and Cytokinesis: Chromosomes gather at the
poles of the cells. the cytoplasm divides.
Stages of Meiosis: Meiosis II
■ Prophase II: A new spindle forms around the chromosomes.
■ Metaphase II: Chromosomes line up at the equator.
■ Anaphase II: Centromeres divides. Chromatids move to the
opposite poles of the cells.
■ Telophase II and Cytokinesis: A nuclear envelope forms
around each set of chromosomes. the cytoplasm divides.
Item 7: Summarize Mendel’s Genetics
Principles
■ Principle of Dominant and Recessive – some genes can
hide or mask others
■ Law of Segregation – Mendel’s genetics principle that
states that genes in pairs separate during gamete
formation and gene pairs are reformed during fertilization
■ Law of Independent Assortment – genes are inherited
separately and that creates a variety in a population
Item 8: Complete Punnett Square to
determine various modes of inheritance
■ Monohybrid crosses – Punnett squares showing one trait at
a time
■ Genotype – the alleles (represented by a letter)
■ Phenotype – the trait seen (physical description)
■ Sex-linked – genes found on the sex
chromosomes
■ In humans, females have 2 X
chromosomes and males have 1 X
chromosome and 1 Y
■ Most sex-lined traits are on the X
chromosome
Example: hemophilia and Duchenne
muscular dystrophy
Sex-Linked Punnett Square Example
■ Allele for the trait is a
exponent on the X
chromosome
■ Females have to have 2
h’s to inherit the
recessive trait
■ Males only need 1 h to
inherit the sex-linked trait
Multiple Alleles Punnett Square
■ Multiple Alleles –
more than 2 alleles
(forms of a gene)
Example: blood
types in humans;
there are 3 alleles
instead of 2; A
gene, B gene, and
O gene
Codominance Punnett Squares
■ Codominance – 2
different alleles that are
both dominant, so in a
heterozygous gene pair,
both traits show up
Example: A and B genes
in human blood type; if a
person is AB genotype,
they make both A and B
proteins and have blood
type AB
Incomplete Dominance Punnett Squares
■ Incomplete Dominance
– heterozygous
genotype gives a
different phenotype
Example: red and
white genes in
Japanese four o’clocks;
a red gene paired with
a white gene makes a
pink flower
■ Polygenic Traits – traits controlled by
more than one pair of genes;
example: human skin color and
human height
■ Dihybrid Crosses – Punnett
squares showing 2 traits; 16
square Punnett squares
Dihybrid Cross Advice
■ On a dihybrid cross, if both parents
are doubly heterozygous, the ratio in
the offspring is 9:3:3:1
■ When determine parents’ potential
gametes use the FOIL method
– First of each allele
– Outside alleles
– Inside alleles
– Last of each allele
RrYy
Item 9: Explain Gene Linkage
■ Discovered after Mendel; states that if genes are on the
same chromosome and located close together, they are
often inherited together
■ Example: red hair and freckles in people
■ Seems to violate Mendel’s independent principle, but as
long as genes are on different chromosomes or found far
apart on the same chromosome, his principle holds true
Item 10: Give examples of both
chromosomal and gene mutations
■ Chromosomal mutations affect a large
part of a chromosome and therefore all of
the genes on that section of the
chromosome
■ Gene mutations only affect one gene and
therefore, one protein
Types of Mutations
■ Deletion mutations –
deletion of a section of
chromosome or one
small section of a gene
Example: cystic fibrosis
■ Substitution mutations
– one base gets
substituted for another
one
Example: in sickle cell
■ Nondisjunction mutations – chromatids or
homologs fail to separate during meiosis;
example: Down’s syndrome is caused from an
extra 21st chromosome
■ Point mutation – affects one amino acid
■ Frameshift – changes a whole sequence of
amino acids
Item 11: Explain the difference between
somatic and germ cell mutations
■ Somatic mutations take place in cells of the
body (skin, muscle, etc.) and are not passed
on to offspring
■ germ cell mutations occur in sex cells and are
passed from parent to offspring
Item 12: Identify Common Mutations
■ Sickle cell anemia – causes abnormally
shaped red blood cells; autosomal recessive
■ Tay-Sachs – mutation in a gene for an
enzyme that functions in the breakdown of a
protein in neurons; autosomal recessive
■ Cystic fibrosis – mutation in a Cl- transport
protein; autosomal recessive
■ Hemophilia – mutation in gene for blood
clotting; sex-linked
More Disorders Caused by Disorders
■ Huntington’s – progressive nervous
deterioration; symptoms don’t occur until
middle age; autosomal dominant
■ Albinism – mutated gene for pigments;
white hair; white skin; usually pink eyes
Mutations caused by nondisjunction
■ Down’s – extra 21st chromosome
■ Klinefelter’s – extra X chromosome;
males; XXY
■ Turner’s – missing X chromosome;
females; XO
Interpret pedigrees to determine how a trait is
inherited in a family
How is this trait inherited?
How is this trait inherited?
Questions?