Lecture 3 E1 -Genetics pt 1 Flashcards
how is genetic material stored
as DNA, a stable macromolecule
what does DNA do
what to do, when , why, and how
Determines disease susceptibility
-many diseases have a genetic component
-most are polygenic, but there are some that are single gene disorders
Determines how we react to drugs
Determines our appearance, like how tall we CAN be
how long can DNA survive?
Through the main stages of replications, cell divisions, renewal and growth
what is a genome, what are the two types
All genes in the body
Nuclear and cytoplasmic
describe the structure of DNA and RNA
DNA and RNA are molecular chains that have a repeating modular structure consisting of two deoxyribose for DNA and ribose for RNA bound to one of the four nucleic acids
what is involved in the actual synthesis of cellular proteins
RNA
four bases
adenine
guanine
thymine
cytosine
which acids are purines, which are pyrimidines
adenine and guanine are purines (teo nitrogenous rings)
thymine and cytosine are pyrimidines (one nitrogen ring)
what is uracil
In RNA, lacks methyl group on its ring, replaces thymine
what is mitochondrial DNA
the cytoplasmic genome
small portion of DNA of a cell resides in mitochondria
double stranded, closed circle, containing 37 genes for DNA translation and oxidative metabolism
what is mitochondrial DNA used for
translation and oxidative metabolism
where is mitochondrial DNA inherited from
usually from the mother only
how does dna exist at resting state
Two strands of DNA running anti-parallel to each other that are wound in a double helical structure
double helix
how are DNA strands held together
Specific hydrogen bonds that form between purines and pyrimidines
what do the purine and pyrimidine specificity cause
DNA strands to be complementary to each other
what does double stranded DNA structure allow
replicating precisely by separation of two strands followed by synthesis of two new complementary strands
what is a gene
piece of DNA that encodes a product
what are genes made up of
pieces of DNA spelling out the genetic code for making a specific protein
how many gene pairs are there
several hundred to 1 million
vary in size
what makes up the alphabet of the genetic code
nitrogenous bases make up alphabet
what makes a codon and how is it decoded
sequence of 3 bases makes a codon which is a nucleotide triplet necessary for protein synthesis
the specific amino acid sequence can be decoded by reading groups of three consecutive bases
what is the template strand
what is transcribed into RNA (into codons)
how many codons are there
64,
each is a 3 base triplet and there are 4 possible bases for each position
what is functional redundancy or degeneracy
meaning that the amino acid can be specified by more than one codon
(most aminos acids are)
ex; AUG serves the dual functions of signaling the start of translation and encoding methionine
what are synonyms of genetic code
codons differing only at third base position will typically code for the same amino acid or amino acids with similar chemical properties
what 3 codons do not signal amino acids
UGA, UAA, UAG
stop or termination codes
how is DNA genetic message delivered to the cytoplasm of a cell
by RNA
How are genes determine?
Hey single alleles meaning monogenic or many alleles polygenic
what do any diseases result from?
Damage to genes are chromosomes.
The damage can be spontaneous or an environmental insult or an inheritable defect
what is mutation considered
Mutation is not associated with a disease phenotype. It is considered a variant or polymorphism.
It typically accounts for differences in gene expression in proteins function that still allow functioning within normal range, contributing to human variability
What are mutations a result of
result of errors in the DNA duplication and become a permanent structural alterations in DNA
Typically refers to changes in the genome that cause sufficient change in expression or function, so that a path of physiological state results
effects of mutations can be variable
How are mutations often resolved?
By DNA repair mechanisms, but these mechanisms can fail, allowing the damage genetic material to be passed on
what is the transmission of genetic mutation affected by
Expressivity of the mutation, or the way the genotype is expressed in the phenotype
Range from mild to severe
what is transmission genetics
Repetition and division of DNA mutations through generations
what is penetrance
The ability of a gene to expressive mutation, which can influence the effects of genetic mutations
what mutations can be transferred generationally
Somatic (generic cells) and germline mutations
what is the most common form of DNA variation?
Single base substitution
What is the single substitution and how is it characterized?
Replacement of one base for another base in the DNA sequence
A single nucleotide polymorphism
well characterized- mendelian disorders - CF
don’t usually cause problems but if it does it is named
what is a nonsense mutation?
Substitution that changes a codon for an amino acid to stop codon, leading to the premature termination of translation of the mRNA transcribed in a truncated protein
what is a missense sense mutation
A substitution that changes the codon for one amino acid to the codon for another amino acid. The size of the mRNA and proteins are not changed but the composition, and possibly the function of a protein does change.
*switch it out mutation
what is a splice site mutation
Substitution in one of the base pairs inside or flanking the intron exon boundaries that alters normal pre-mRNA splicing.
Such mutations can result in an intron retention(partial or complete) or exon skipping.
what is a silent mutation?
A change in one base that results in no change in the amino acid sequence of the proteins, due to the redundancy of the genetic code
(There is more than one codon for most amino acids)
what is a regulatory polymorphism?
a substitution that alters binding affinities of transcription related proteins, such as transcription factors, enhancers, silencers, or insulators
may show up in wrong spot
Such changes result in altered rates of transcription
what is RNA?
Molecule that is responsible for the assembly of our proteins
RNA versus DNA
Is single-stranded, the sugar backbone of RNA is ribose, the pyrimidine base uracil for RNA replaces thymine for DNA
what is the messenger RNA
Provides a template for proteins synthesis, depending on the codon sequence of the DNA strand
Carries instructions from the DNA molecule into the cytoplasm
Formed by the process of transcription
what is ribosomal RNA
Ribosome is the structure of the cytoplasm where proteins synthesis takes place
Makes up a ribosomes, which are transported from the nucleus to the cytoplasm, and begin proteins synthesis, or translation of the genetic code
what is transfer RNA
A clover shaped molecule that functions to deliver the activated form of amino acid to the proteins that is being synthesized in the ribosomes
Each tRNA recognizes and binds a specific amino acid, which it transfers to ribosomes
*brings amino acids into complex to make new proteins
What is transcription?
Involves the copying of the genetic code from DNA to a complementary strand of mRNA
What is a template strand
RNA polymers reads from this to make a copy of the DNA to RNA
Where does transcription happen?
nucleus
what is transcription initiated by?
Enzyme called RNA polymerase, which binds to a specific promoter site on the DNA
when does transcription stop?
Transcription will continue to copy the strand of DNA until it reaches a terminator
now it can be processed (adding cap, tail, splicing)
What happens after a terminator is reached in transcription
RNA polymerase enzyme will leave the gene and release the premature RNA strand for further processing
what are the beginning and end of a gene called
promotor, terminator
post transcription modification of mRNA
RNA transcription is a continuous process, yet the DNA sequence that codes for proteins (exons) is often interrupted by interviewing, non-coding sequences(introns)
These intron segments must be removed or spliced from the RNA prior to translation
What does the splicing process lead to?
Several different proteins from one gene as you can mix and match exons together
what does differential splicing of coding exons result in?
Differences in the ultimate proteins structure
what happens once mRNA has been processed
Diffuses through the nucleus pores into the cytoplasm, where it will travel to the ribosomes and control proteins synthesis
Why do we keep introns
Because they allow the synthesis of more than one protein from the same gene
what is mature mRNA made of
only exons
example of alternative splicing
leaving out one exon would have the same sequence but would make a different protein
what is translation?
The process of taking the instructions from the mRNA, and transferring them to the rRNA of ribosomes located in the cytoplasm
mRNA binds to ribosome and is transcribed and instructions sent to tRNA to transfer the correct amino acid to the growing peptide chain
Newly synthesize proteins and folds into its functional form and is sent to its final position in the cell
What are chromosomes
Chromosomes are composed of double strand of DNA containing sections of genes
what happens to chromosomes during cell division
Chromosomes reproduce their physical and chemical structures to pass on genetic information in one of two processes
mitosis or meiosis
What is mitosis?
Chromosomes in the nucleus of somatic cells, go through a series of phases, resulted in the creation of daughter cells with the same chromosome number, and genetic make up as the original cell
what is meiosis
Process where one germ cell divides into for cells, each with half set of chromosomes
What is ploidy?
The number of sets of chromosomes you have
somatic cells chromosomes
Somatic cells contain chromosome pairs
Each somatic cell contains two sets of 23 chromosomes, diploid number of chromosomes
44 chromosomes are autosomes, and two are sex chromosome (X,Y)
what are gametes
Ova and sperm
contain only one set of chromosomes
haploid number of chromosomes
what results in the diploid number of chromosomes
combination of ova and sperm genetic material at the time of conception results in a cell with the diploid number of chromosomes
what are somatic cells
non reproductive
23 pairs of diploid chromosomes
formed during mitosis
what are gametes
reproductive cells
contain 23 single stranded chromosomes (haploid)
formed during meiosis
describe mitosis
-process in which somatic cells replicate and divide to produce identical daughter cells each with 23 pairs of chromosomes
what are daughter cells
same chromosome number and genetic makeuo as original cell
what are the four phases of mitosis
prophase, metaphase, anaphase, telophase
what is meiosis
process in which gametes (reproductive cells) are formed
each cell contains single set of 23 chromosomes
what is spermatogenesis
production of viable spermatids
what is oogenesis
production of one viable ovum and three polar bodies (of 4 produced, 3 degenerate along the way and only one turns into an egg)
what is dijunction
when chromosomes separate during mitosis and meiosis
what is recombination
process of chromosomes coming back together in mitosis and meiosis
what is nondisjunction
when chromosomes(sister chromatids) fail to separate (when they should during disjunction)
- one cell gets an extra and one gets none
aneuploidy
- results in unequal number of chromosomes between cells
-not the whole set but 1-2 chromosomes may get extra - ## common in meiosis in people
is aneuploidy more common in sperm or eggs
eggs
polyploidy
not common in humans, more common in nature
results form chromatids not pulling apart, you get multiple sets)
how many newborns does aneuploidy affect
1:300
what increases risk of aneuploidy
maternal aging
5% at age 30
10% age 35
15% age 39
35% age 42
what age group is at risk for aneuploidy
young teens (less than 16 years)
how is aneuploidy written
n+- # of extra chromosomes you have (or dont have)
-omy
aneuploidy
-ploidy
polyploid (triploid)
monosomy
(one-aneuploidy)
presence of only one member of a chromosome repair (missing one of a pair)
occurs when nondisjunction results in cells with one copy of a chromosome instead of two
usually incompatible with life
exception is turner syndrome (chrom 45, missing X)
what is turner syndrome
absence of all or part of X chromosome (monosomy)
most common genetic disorder in women
short stature, wide set nipples, webbed neck
no secondary sex characteristics
normla intelligence
often diagnosed with short stature or failure to enter puberty
what is polysomy
presence of more than two chromosomes to a set
when does polysomy occur
when a germ cell containing more than two chromosomes is involved in conception
what is trisomy
presence of three copies of a chromosome per cell
if large chromosome is affected, excess of genetic material is incompatible with life
trisomy 21
most common
down syndrome
trisomy 13 and trisomy 18
edward syndrome
more severe and result in early death in most cases
can trisomy of sex chromosomes occur
yes, and it is more compatible with life
47, XXY kleinfelter syndrome
47, XXX triple X syndrome
down syndrome
first described 1866
most common chromosomal disorder
increased risk with advanced maternal age
95% due to nondisjunction during meiosis- trisomy 21
characteristics-
flattened nasal bridge, epicanthal folds, protruding tongue, simian crease
prenatal screening- AFP, hCG, PAPP-A, nuchal translucency, *karyotype most accurate
kleinfelter syndrome
extra X chromosme (polysomy)
nondisjunction during meiosis, usually maternal
1:1000 males, many unaware
enlarged breasts, sparse body hair, small testes, high voice
infertility, osteoperosis later
treated with androgens
(lower IQ than sibs, tall stature, poor muscle tone)
mosaicism
presence of two or more genetically different sets of cells
result from early errors in mitosis
expressed in a percentage based on blood analysis
if mosaicism made up of normal and abnormal karyotype, deformities less severe
(can affect pigmentation, some cancers)
mitochondria mutation (cells can end up with functioning or mutated mitochondria)
random X inactivation ( parts of body may express dads or moms X chromosome)
what is linkage/recombination
typically alleles of different genes sort independently during meiosis but
genetic linkage- genes in close proximity sort together
crossing over/homologous recombination- when genes of same chromosome sort independently
structural abnormalities of mutations
occurs due to breakage and subsequent rearrangement or deletion
multiple patterns (deletion, translocation, inversion, insertion, duplication)
structural rearrangements leads to changes in base pairs, thus errors in transcription, abnormal proteins, and mutations in the individual
when does translocation occur
when a large segment of DNA breaks from one chromosome and reattaches to a different chromosome, often during meiosis
balanced vs imbalanced translocation
if its balanced, the translocation does not affect the individual because the amount of genetic material remains the same
if its unbalanced, it will have significant affects due to missing or excessive genes
familial down syndrome mutation
most frequently encountered translocation
translocation between chromosome 14 and 21
deletion
removal of part of chromosome
causes mutation
duplication
doubling part of a chromosome
increases genetic diversity in populations
inversion
putting piece of chromosome upside down on opposite chromatid
may cause problems with gene expression, histone remodeling due to changed place
