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81 Cards in this Set

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Gene
Basic Unit of Heredity

Composed of DNA

Located on Chromosomes
What is an allele?
When a gene exists in more than one form.
Genotype
Genetic makeup of an individual
Phenotype
Physical manifestations of the genotype
Mendelian Genetics
1860s

Gregor Mendel

Basic principles of genetics through experiments with garden pea plants.

Studied inheritance by performing genetic crosses of true breeding individuals and statistically analyzed the inheritance of the traits in the progeny.
Mendel's First Law: Law of Segregation (4)
Genes exist in alternative forms (now called alleles)

An organism has two alleles for each trait, one from each parent

Two alleles segragate during meiosis resulting in gametes that carry only one allele for any given inherited trait. If two alleles are different, one will be expressed and one will not.
Dominant and recessive allele
Dominant - Expressed Allele
Recessive - Hidden Allele
Homozygous
Organisms with two copies of same allele
Heterozygous
Organisms that contain two alleles
Mendel's Law of Dominance
Yy will appear as yellow as YY
Monohybrid Cross
Only one trait being studied

PP x pp = (4) Pp 100% heterozygous Dominant
Mendel's Second Law: Law of Independent Assortment
Dihybrid Cross

As long as two genes are on different chromosomes, they will assort randomly.

If on same chromosome, they will stay together unless crossing over occurs.
Dihybrid Cross
Parents differ in two traits

TTPP x ttpp
|
V
F1 genotypes: 100% TtPp
|
V
self-cross: TtPp x TtPp
|
V
Horizontal: TP tP Tp tp
Vertical: TP tP Tp tp
Incomplete Dominance
Blends of parental Phenotype

Pink is result of red and white genes in heterozygotes.
Codominance
Multiple alleles exist for a gene and more than one of them is dominant

NOT a blend, both dominant alleles are expressed simultaneously

Example: ABO blood type
Sex Determination
Humans have 22 pairs of autosomes, 1 pair of sex chromosomes

Sex Chromosomes:
Female - XX
Male - XY
Sex Linked Genes
Genes that are located on X or Y chromosomes

In humans, most are on X chromosome
Sex-Linkage of Genes
Females:
XX

Males:
XY - recessive allele on X is unsuppressed by Y -> X is expressed
Why is Drosophila Melanogaster used?
Reproduces often
Reproduces in large number
Chromosomes are large and easily recognizable in shape and size
Few chromosomes
Mutations occur relatively frequently
Can genes be affected by the environment?
Yes in development different temperatures result in different phenotypes.
Genetic Problems - Nondisjunction
Failure of homologous chromosomes to seperate properly during meiosis I, or

Failure of sister chromatids to seperate prperly during Meiosis II.

Zygote may have three copies of chromosome (trisomy) or single copy of chromosome (monosomy)

Most monosomies and trisomies are lethal.
Down's Syndrome
Trisomy of chromosome 21
Genetic Problems - Chromosomal Breakage
Can occur spontaneously, or

Can be induced by environment such as mutagenic agents or X rays.
Genetic Problems - Mutations
Changes in the genetic information of a cell, coded in DNA.
Result of somatic cell mutations?
Tumors within the individual
Result of sex cells mutations?
Defects or mutations in offspring
Mutagenic Agents
Can induce mutations

Cosmic rays, X-rays, ultraviolet rays, radioactivity, chemicals

Generally carcinogenic as well
Mutation Types
Nitrogen bases are added, deleted, or substituted
Phenylketonuria (PKU)
Molecular disease caused by the inability to produce the proper enzyme for the metabolism of phenylalanine
Sickle-cell Anemia
Red blood cells become crescent shaped due to defective hemoglobin.

Carries less oxygen.

Due to a single base pair substitution.
What is the basic unit of a nucleotide?
DNA
What is DNA composed of?
Deoxyribose + Phosphate group + Nitrogenous base
What types of bases are there for DNA?
Purines and pyridamines
Which bases are purines and which are pyridamines
CUT PIE

C ytosine
U racil
T hyamine are
PY rimidines

Adenine and Guanine are purines
What bases are in DNA?
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
How is the double stranded helix arranged?
Sugar-phosphate chains on outside, bases on inside.
How do the bases bond to each other?
T-A (2 Hydrogen Bonds)
G-C (3 Hydrogen Bonds)
What is semiconservative DNA replication?
Parent - A
Daughter - B

Original DNA strand: AA
2 Copied DNA strands: AB BA
What is conservative DNA replication?
Parent DNA is copied completely and kept in tact after.

Parent - A
Daughter - B

Original DNA strand: AA
2 Copied DNA strands: AA BB
Is the genetic code universal among all organisms?
Yes, the code is universal.
What does degeneracy or redundancy of genetic code mean?
Most amino acids have more than one codon specifying them.
DNA in a Nutshell
DNA -> DNA = replication (new DNA synthesized in 5'->3' direction)

DNA -> RNA = transcription (new RNA synthesized in 5'->3' direction)

RNA -> protein = translation (mRNA read in 5'->3' direction)
What are the three differences between RNA and DNA?
For RNA:

Sugar is ribose

Contains Uracil (U) instead of Thymine (T)

Usually Single Stranded
Where is RNA found?
Both cytoplasm and nucleus
What are the types of RNA?
mRNA
tRNA
rRNA
What is Messenger RNA (mRNA)?
mRNA carries the complement of a DNA sequence and transports it from the nucleus to the ribosomes, where protein synthesis occurs.

mRNA is the complementary codes of the orginal master DNA

mRNA is monocistronic, one mRNA strand codes for one polypeptide
monocistronic
one mRNA strand codes for one polypeptide
What is Transfer RNA (tRNA)?
Small RNA found in cytoplasm which aids in the translation of mRNA's nucleotide code into a sequence of amine acids.

tRNA brings amino acids to the ribosomes during protein synthesis. There are at least one type of tRNA for each amino acid.
What is Ribosomal RNA (rRNA)?
Structural component of ribosomes and is the most abundant of all RNA types

Synthesised in the nucleolus
What is transcription?
Transcription is process where DNA is transcribed into strand of mRNA.

mRNA leaves nucleus to cytoplasm where the remaining protein synthesis events take place.
What is translation?
Process in which mRNA codons are translated into a sequence of amino acids

Occurs in cytoplasm

involves tRNA, ribosomes, mRNA, amino acids, enzymes and other proteins
What does tRNA do in translation?
tRNA brings amino acids to the ribosomes in the correct sequence for polypeptide synthesis

tRNA "recognizes" both the amino acid and the mRNA codon

This dual function is reflected in its three dimensional structure: one end contains a three-nucleotide sequence, the anticodon, which is complementary to one of the mRNA codons; the other end is the site of amino acid attachment.

Each amino acid has its own aminoacyl-tRNA synthetase, which has an active site that binds to both the amino acid and its corresponding tRNA, catalyzing their attachment to form an aminoacyl-tRNA complex.
What do ribosomes do in translation?
Composed of two subunits: proteins and rRNA that bind only during protein synthesis

Ribosomes have three binding sites: one for mRNA, two for tRNA (P and A sites).

P site: binds to the tRNA attached to the growing polypeptide chain

A site: binds to the incoming aminacyl-tRNA complex
What are the three steps of Polypeptide Synthesis?
initiation
elongation
termination
Where does initiation begin?
Begins when the ribosome binds to the mRNA near its 5' end. Scans mRNA until it binds to a start codon (AUG).
What occurs during elongation?
Hydrogen bonds form between the mRNA codon in the A site and its complementary anticodon on the incoming aminoacyl-tRNA complex.

Peptide bond is formed between the amino acid attached to the tRNA in the A site and the met attached to the tRNA in the P site.

Ribosome carries uncharge tRNA in the P site and peptidyl-tRNA in the A site.

Completed by translocation in which the ribosome advances 3 nucleotides along the mRNA in the 5' to 3' direction.

Concurrent action, uncharged tRNA from P site is expelled and the peptidyl-tRNA from the A site moves into the P site.

Ribosome now has empty A site ready for entry of the aminoacyl-tRNA corresponding to the next codon.
How does polypeptide synthesis terminate?
When one of three special mRNA termination codons (UAA, UAG, UGA) arrives in the A site.
What happens when the polypeptide is released from the ribosome following synthesis?
The protein immediatly forms its native conformation determined by the primary structure
Cytoplasmic Inheritance
DNA is found outside nucleus.

Found in chloroplasts and mitochondria.

These cytoplasmic genes may interact with nuclear genes and are important in determining the characteristics of their organelles.

Drug resistance is often regulated by cytoplasmic DNA called plasmids that contain one or more genes.
What is different about bacteria genome?
Single circular chromosome located in nucleoid region of the cell.
What are plasmids and do bacteria have them?
Yes, they are smaller circular DNA rings.
What are episomes?
Plasmids that are capable of integration into bacterial genome.
Bacterial Replication
Begins at unique origin of replication

Proceeds in both directions simultaneously

DNA synthesized in 5' to 3' direction
How do bacterial cells normally proliferate under favorable conditions?
Via binary fission.

Asexual process.
What three mechanisms do bacteria have for increasing the genetic variance of a population?
Transformation
Conjugation
Transduction
Bacterial Genetic Variance - Transformation
Foreign chromosome fragment (plasmid) is incorporated into the bacterial chromosome via recombination, creating new inheritable genetic combinations.
Bacterial Genetic Variance - Conjugation
Sexual mating in bacteria.

Transfer of genetic material between two bacteria temporarily joined.

Only bacteria containing plasmids called sex factors are capable of conjugating.

F+ cells can donate to F- cells, turning F- into F+

Complete transfer of DNA is not common due to linkage break
Bacterial Genetic Variance - Transduction
Occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny produced during viral infection.
Bacterial Genetic Variance - Recombination
Occurs when linked genes are seperated.

Occurs when organisms carrying different genes or alleles for the same traits are crossed.
What are Bacteriophages?
Virus that infects host bacterium.

Once inside host, bacteriophage enters lytic cycle or lysogenic cycle.
What is Bacteriophage Lytic Cycle?
Manufactures numerous virus progeny.

Bacterial cell bursts, allowing infection of other bacterium.

Bacteriophages that use lytic cycle are called virulent.
What is Bacteriophage Lysogenic Cycle?
If cell doesn't lyse, viral DNA becomes integrated into the bacterial genome in a harmless form (provirus), lying dormant for one or more generations.

Normally stay dormant until spontaneous or induced entrance into lytic cycle.
How do prokaryotes regulate metabolism?
By the regulation of gene expression (transcription)
What is the regulation of transcription based upon?
Accessability of RNA polymerase to the genes being transcribed, and

is directed by an operon, consisting of structural genes, operator gene, and a promotor gene.
What are structural genes?
Contain sequences of DNA that code for proteins
What are operator genes?
Sequence of nontranscribable DNA that is the repressor binding site.
What is the promotor gene?
Noncoding sequence of DNA that serves as the initial binding site for RNA polymerase.
What is a regulator gene?
Codes for the synthesis of a repressor molecule that binds to the operator and blocks RNA polymerase from transcribing the structural genes.
What is important about the operator gene for transcription?
In order for transcription to take place, the RNA polymerase must move past operator gene.
How do regulatory systems work?
Regulatory systems work by preventing or allowing RNA polymerase from passing the operator region.

Regulation occur via inducible or repressible systems.
What is an inducible sytem?
Inducible systems are those that require the presence of a substance, called in inducer for transcription to occur.

Repressible systems are in a constant state of transcription unless a corepressor is present to inhibit transcription.