Flashcards in Exam 4 Deck (78):
What are chromosomal aberrations and what are the types?
CHANGES IN THE NUMBER OF CHROMOSOMES
- extra COMPLETE sets of chromosomes
- 3N or more
- suffix: ploid or ploidy
- extra or missing SINGLE chromosomes
- 2N+1 or 2N-1
- suffix: somy or somic
- more common (less drastic change)
CHANGES IN CHROMOSOME STRUCTURE
Changes in the number of genes
Changes in the location of genes (Position Effects)
- robertsonian changes
What is a position effect?
Movement of genes
Genes that are normally off get turned on when moved
Genes normally turned on get turned off when moved because they're under regulatory control of surrounding genes
eg. why pancreas cells produce insulin
When does haploidy occur?
Rare in animals
- exception: bees (male haploid; females diploid)
Common in plants
- alternation of generations
- don't do as well as diploid plants
When does triploidy occur?
Not common in animals
most common form of polyplidy in animals
- due to double fertilization (2 sperm w/ 1 egg)
- if organism survives it's sterile (pairing of homologs in meiosis is disrupted)
- survival is very rare
What's the difference between odd numbered and even numbered ploidy's?
Even numbered ploidy's (if they can survive) can reproduce b/c synapsis w/ an even number of chromosomes is easier to accomplish then an odd number
How does polyploidy affect plants?
Polyploidy generally improves viability in plants
- plants are larger, stonger
- pairing at meiosis is still problem w/ odd ploidies but can reproduce asexually also
What is the 2n+/- for tetrasomy, monosomy, trisomy? What happens the further away from 2N you get?
The further away from 2N you get the less likely the creature will survive
- Pentasomy 2N+3 unlikely
What is disjunction? What is non-disjunction?
separation of homologs or chromatids
Type of aneuploidy where a random error where homologs or chromatids don't separate
- random error so equally likely to occur to any chromosome
- gamete has 2 copies or NO copies of one chromosome
Fetus usually not viable
Work through non-disjunction at the 1st meitotic division and then the 2nd meitotic division.
Non-disjunction at 1st meiototic division:
- all gametes affected
Non-disjunction at 2nd meiototic division:
- 1/2 gametes affected
What is down syndrome?
- Aneuploidy: non-disjunction that results in two copys of chromosome 21's
- 20% born, 20% stillborn, 60% lethal in utero
- not a genetic condition (random error) so doesn't run in family
- higher incidence w/ maternal age (more likely the nondisjunction occured w/ mom)
What is klinefelter syndrome?
47 Chromosomes; XXY
- nondisjunction of the X chromosomes
- often asymptomatic (male)
Small testes; low testosterone
- poor secondary sex characteristics
- female characteristics
What is Jacobs syndrome?
47 chromosomes; XYY
- nondisjunction of the Y chromosomes
- "criminal chromosome"
- lower avg intelligence; learning disabilities
- above avg height + severe acne
What is Turner syndrome?
45 chromosomes; XO (monosomy)
- asymptomatic until puberty
- no puberty; lack of secondary female characteristics
What is 47 XXX?
47 chromosomes; XXX
- some sterility and some mental disabilities
Why are most of the aneuploids that survive involve the X chromosome?
The extra X chromosomes become extra barr bodies
- not really an extra entire chromosome
What is a deletion?
removal of a small gene (piece of a chromosome) in the entire organism (not just a single somatic cell)
- Sometimes chromosomes just break (fragile spots or environmental causes) and rejoin w/o broken piece
- Unequal crossing over; synapsis occurs and the end result is a duplication of one gene on one chromosome and a deletion of that gene on the other chromosome
What is the difference between Prader-willi and Angelman Syndromes?
Deletions of same chromosome
Both are the result of the same part of chromosome 15 being deleted but it depnds on if the sperm or the egg had part of chromosome 15 deleted
- sperm = prader-willi
- egg = angelman
What is a duplication?
Redundant segment of a chromosome typically from unequal crossing over
- allows development of new related genes
- duplicated gene may mutate and produce new gene version (allows 1 copy to mutate)
How did different types of globin molecules arise?
Single Globin gene that worked in muscle and RBC
- then had a duplication and that results in 1 globin that works better in muscle and one that works better in RBC
- then another duplication in globin that allowed for mutation that caused two types of hemoglobin (alpha and beta)
How can you get down syndrome w/o having trisomy 21?
Having 3 copies of the Nucleolar organizer region due to a duplication causes downs
- still 2 chromosomes but have 2 copies of one region
What is an inversion?
When you take a segment of chromosome and turn it 180 degrees and reinsert it.
- could end up turning on/off these genes in the surrounding regions (position effects)
Caused by breakage and reannealing of chromosome but backwards
What are translocations?
Exchange of segments between non-homologous chromosomes
- breakage and reunion between NON-homologs
Causes impaired fertility
- only 1/3 segregations will lead to usable gametes
- fertility reduced by 2/3 because 2/3 of gametes are unbalanced
Causes formation of an octad instead of tetrad
- have crossing over
- when pulling apart so you have right amount of material in each gamete (not too much not too little)
May lead to changes in phenotype due to position effects
Translocations in specific somatic cells will cause cancer
- doesn't need to occur throughout body
- same translocation in different somatic cell might not cause cancer (oncogenes)
What is an oncogene?
genes involved in cell proliferation
- normally only active at specific times during development then get turned off
- turn back on get cancer
What is the philadelphia chromosome?
weak spot in both chromosomes 9 & 22
- makes translocations possible
- if translocation occurs = turn on oncogene = cancer
What is burkitts lymphoma?
Translocation between chromosome 8 and 1 of 3 other chromosomes turns on oncogene
What is a transposition?
Movement of small chromosomal pieces to new area of same chromosome or to non-homologous chromosome
Transposon - small segments of DNA capable of transpositions
What is a robertsonian change?
- 2 chromosomes join to form 1
- 1 chromosome splits to form 2
What is familial down syndrome?
Down syndrome that is hereditary
- passed from parent to child
- fusion of chromosome 14 + 21
Carriers are phenotypically normal
- children will be 1:1:1; normal:carrier:down syndrome
What is the central dogma of molecular biology?
DNA -> RNA -> Polypeptide
- through transcription and translation
How is the cell a factory?
Cell is a factory that produces:
- structural proteins
What is a polypeptide?
chain of amino acids
- structural genes code for amino acids
- a functional polypeptide (doing something) it's called a protein
- one gene = one polypeptide
What is sickle cell anemia?
Hemoglobin can't carry oxygen to tissues
- causes RBCs to collapse into sickle shape clogging
Beta polypeptide error causes sickle cell
- error on single allele that codes for single amino acid causes the error on the polypeptide
How is a prokaryote cell a factory?
"Mom and Pop" factory
- no nucleus so no head office
- all products made at some time or other (not all at same time)
How is eukaryote cell a factory?
- Has nucleus where DNA kept
- specializes in some products (eg. pancreas insulin)
- not all products made all the time
What gives amino acids different properties?
- polar, basic, acidic neutral
How are amino acids connected to form a polypeptide?
- carboxyl end of 1 AA to amino end of next AA
- dehydration rxn to make peptide bond
COOH + NH2 => CO-NH + H20
- the peptide bond is a C-N bond
Where does a new amino acid get added when coding for a polypeptide?
the new amino acid gets attached to the carboxyl end
amino acid is read from amino end (front) to the carboxyl (back) end
- this corresponds to the 5' to 3' direction of the gene that coded for it
What is the primary structure of proteins?
What amino acids you have in polypeptide
- what DNA is directly coding for
What is the secondary structure of proteins?
first folding that takes place
- based on Hydrogen bonding between the H left on the amino group of 1 AA and the O left on the carboxyl of another AA
What are alpha helices and beta pleated sheets?
portion of chain coils up
portion of the chain folds back on itself
What is tertiary structure?
second folding based on interactions between R-groups
- covalent bonding
- ionic bonds
- vaan der waals interactions
What is quarternary structure?
if polypeptide is a functional protein then no quarternary structure
if it takes more than 1 polypeptide to make functional protein then it takes on quarternary structure
- third folding due to interactions between polypeptides
What is the purpose of transcription?
working copy of gene that can be released into the cytoplasm then translated into working polypeptide protein
What is DNA? When is it copied?
- only copied when you need to make a new cell (new 'factory')
Going back to the cell as a factory analogy, what would RNA, Cytoplasm, Ribosomes, and tRNA be?
RNA - working copy of gene
Cytoplasm - work floor
Ribosomes - machinery
tRNA - workers
How does the cell stamp RNA as the working copy and not DNA?
(difference between DNA and RNA)
ribose instead of deoxyribose
uracil replaces thymine
single stranded molecule instead of double stranded
What are the types of RNA?
mRNA - carries genetic msg to be translated into polypeptide
tRNA - translator molecule
rRNA - structural component of ribosomes
hnRNA - heterogenous nuclear RNA
ALL TYPES ARE TRANSCRIBED FROM DNA!!!
How many strands of DNA are transcribed?
only one strand of DNA is transcribed
- for any given gene there's only one strand carrying the information we need
- this one strand is the gene
If you want RNA copy of that information then you must use the opposite strand as a template
- gene does nothing
- opposite TEMPLATE (3' to 5') strand is used to make working SENSE (5' to 3') strand
What is a promotor?
Lets you know what you're transcribing
- promotor is specific for gene
Special sequence of bases that signal start of gene
- know where to start the transcription process
ONLY place RNA Polymerase can attach
- initiates localized melting of DNA double strand
What is one of the advantages of having double stranded DNA?
You can fit more information
- different genes can use different strands as template strand
What is the sense strand and template strand?
- information we want
- coding strand
- the gene
- what we use
- nonsense strand
- non-coding strand
RNA is the perfect copy of the sense strand
- except Uracils are substituted for thymines
- use the template strand to make this copy
What is the difference between upstream vs downstream?
upstream is toward the 5' end of the sense strand
What are the regions of the gene?
Promotor: promotes transcription
Terminator: stops transcription
Leader region: doesn't carry coding info - regulatory
- not translated
- in the promotor region
- allows 5' end of mRNA to attach to ribosome
Trailer region: extra info
- not translated
- in the terminator region (3' end)
Coding Region: codes for gene product
- called open reading frame
- actually translated
Leader, Trailer, Coding regions are for translation
What are the parts of the open reading frame?
start codon sets up reading frame
- so you know the next 3 bases are a codon, then next 3 bases are a codon etc
- ends translation
REMEMBER THIS IS FOR TRANSLATION!
What are the characteristics of promotors?
- the same sequences
- lots of A-T pairs (fewer H bonds = less energy to pull apart)
What are the characteristics of the prokaryotic promotor?
10 bases to 35 bases upstream from where you start transcription
- called -10 box and -35 box
- lots of A-T's
What are the characteristics of eukaryotic promotors?
TATA Box: -25 box
CAAT Box: -75 box
nothing but A-T at the end of promotor region next to ORF allows the template/sense strands to be separated
What are the steps of transcription?
- RNA Polymerase binds DNA
- separates strands and starts transcription
- RNA strand is transcribed and grows as you bring in the mRNA nucleotides
- reach terminator region and ends translation
do introns exists on mRNA? What is mRNA before?
no. undergone post translational modificatoin
- primary transcript before ptm
do prokaryotes have introns?
there is no post-translational modification on prokaryotes
How does termination occur in prokaryotes?
Rho-independent (2 things to stop transcription)
- inverted repeats
- series of uracils due to thymines on sense strand
Rho-dependent (has Rho to stop transcription)
- may/may not have inverted repeat
- rho factor (protein)
What are inverted repeats?
sequence of bases that read the same 5' to 3' on one strand as they read 5' to 3' on the other strand
affect RNA because the single strand has alot of complimentary bases that fold up on eachother
- called a stem loop or hairpin turn
- if you get this while RNA polymerase is transcribing it will get stuck
- A-U linkages on transcript break and RNA released from DNA
How does termination occur in eukaryotes?
Enzyme recognizes termination sequence in the trailer region
- the nuclease cuts phosphodiester bonds in RNA
How does termination occur in eukaryotes?
Enzyme recognizes termination sequence in the trailer region
- the nuclease cuts phosphodiester bonds in RNA to release transcript
What has to be done before a terminated transcript can be called mature working mRNA?
- addition of methyl-guanine cap to 5' end
- addition of Poly-A tail to 3' end
- Excision of introns
What are introns vs exons?
- expressed sequences
- coding portion
- intervening sequences
- do not carry information for polypeptide
- need to be removed or else you'll make an entirely different polypeptide
What is used to splice out introns?
RNA molecules called snRNA's
- small nuclear RNAs
What happens to the excised introns?
What is the general overview of translation?
mRNA carries the message
tRNA translates the mRNA
- using anticodon
Ribosome puts it all together
- rRNA + protein
What are the characteristics of tRNA?
transcribed from DNA like any other RNA
binds to other nucleic acids (mRNA)
binds to amino acids
inverted repeats create stem loops on tRNA
anticodon binds mRNA and brings in correct amino acid
each tRNA is differently shaped that fits the enzyme that brings in the correct corresponding amino acid
What is charging a tRNA?
process of attaching correct amino acid to correct tRNA
When you get tRNA bonded to amino acid + enzyme
- enzyme forms bond between AA + tRNA and then detaches
What are the start and stop codons?
- UGA, UAA, UAG
What are the characteristics of the genetic code?
- each base belongs to one codon only
every 3 bases = 1 codon
no bases are skipped
What happens to the methionine that is coded for by the start codon?
typically the methionine is not needed
- prokaryotes clip it off w/ enzyme
What is the overall structure of the ribosome?
Small and large subunits
The large subunit contains the following sites:
- aminoacyl site = A (entry) site
- peptidyl site = P (donor) Site
- Exit site = E site
Go through the beginning of translation in eukaryotes.
RIbosome fully assembled
- mRNA comes out of nucleus and attaches to ribosome
- sequences of bases in 5' leader region that are complimentary to rRNA (like a magnet)
- mRNA moves along through ribosome (scanning) until first AUG (start) in P site
tRNA carrying methionine w/ it's anticodon (UAC) will hydrogen bond to mRNA
Go through the beginning of translation in prokaryotes.
RIbosome not fully assembled (large subunit not attached)
RIght before first AUG we find the shine-dalgarno sequence
- sequence of bases in mRNA that is complementary to rRNA that places the AUG in the P site (no scanning)
tRNA carrying methionine attaches to mRNA then large subunit attaches