bio final Flashcards
true or false? a haploid organism has one pair o homologous chromosomes
false
when do sister chromatids f each chromosome separate meiosis
meiosis ii
what is an x shaped structure formed from the crossing over of homologous chromosomes, which can then exchange segments at the crossover sites
chiasma
what is the composition of a tetrad at the beginning of prophase i
one pair of homologous chromosomes
what is a tetrad
one chromosome in a tetrad is paternally inheretid, while the other is maternally inherited. each chromosome consists of two chromosomes
when do sister chromatids separate meiosis
anaphase ii
synapsis
pairing of homologous chromosomes that occurs during prophase i
when do homologous chromomsomes migrate to opposite poles
anaphase i – the sister chromatids remain attached at their centromeres
HOW DO CELLS AT THE COMPLETION OF MEIOSIS COMPARE WITH THE CELLS THAT ARE IN PROPHASE OF MEIOSIS I
THEY HAVE HALF THE NUMBER OF CHROMOSOMES AND one-fourth the amount of dna
sister chromatids separate from each other during when
mitosis and meiosis ii
what syndrome is characterized by the xo chromosome abnormality
turner syndrome
when can nondisjuntion occur
- in mitosis or meiosis, when sister chromatids fail to separate
- in meiosis, when homologous chromosomes fail to separate
what type of chromosome abnormality is most likely to be viable in humans
trisomy
short segments of newly synthesized DNA are joined into a continuous strand by
ligase
the first step in the replication of DNA is catalyzed by what
helicase (unwinds double helix)
what catalyzes DNA synthesis
DNA polymerase
what enxyme is important for relieving tension in a helix as it unwinds during DNA synthesis
topoisomerase
when are single stranded DNA molecules antiparallel
when they are lined up next to each other but oriented in opposite directions
what does a single-strand binding protein do, and where does it bind
prevents H-bonds between bases, binds after the replication fork
eukaryotic telomeres replicate differently than the rest of the chromosome. THis is a consequence of what
the gaps left at the 5’ end of the lagging strand
if newly synthesized DNA is found in fragments, whta isnt working
ligase
what is a major difference between eukaryotic DNA replication and prokaryotic DNA replication
projaryotic chromosomes have a single origin of replication, whereas eukaruptic chromosomes have multiple origins of replication
where does telomerase bind
the overhang at the end of the chromosome
template for telomerase
RNA template
what does a nonsense mutation do
leads to early termination of protein synthesis
when does protein synthesis end
when a sop codon is produced
what does a silent mutation do
results in the insertion of the same aminio acid as was coded for by th eoriginal sequence
base subsitution mutations alter a what
nucleotide
a missense mutation does what
dramatically alter protein structure
what untwists a portion of the DNA double helix for RNA transcription
RNA polymerase
region of DNA at which the process of transcription begins
the promoter
site in dna that recruits the rna polymerase
promoter
nontranscribed region of a gene
promoter
where are ribosomal subutits formed
nucleolus
where does transcription and RNA processing occur
nucleus
interons are removed from the pre RNA by what
snRNAs
what is added to the 5’ end of the pre-mRNA
a cap consisting of a modified guanine nucleotide
what is added to the 3’ end of the pre-mRNA
a poly-A tail (50-250 adenine nucleotides)
in eukaryotic cells, transcription cannot begin until when
several transcription factors have bound to the promoter
the -10 box and the -35 box two regions of a bacterial promoter do what
bind to the sigma subunit that is associated with RNA polymerase
how does termination happen
when release factors recognize the stop codon in the A site and catalyze the release of the polypeptide from teh tRNA in the P site
what enxyme catalyzes the attachment of an amino acid to tRNA
aminoacyl-tRNA synthetase
the initiator tRNA attaches at the ribosome’s what site
P
where does amino acid bind to a tRNA
the part that sticks out at the 3’ end
where do regulatory proteins bind in bacteria
the operator
in lac operon what is the regualtory gene
lacI
why are the genes involved in lactose metabolism considered to be an operon
they are all controlled by the same promoter
addition of what short proteins in eukaryotes target proteins for destruction by protasom
ubiquitins
enzyme complexes that break down protein are called what
proteasomes
protein-phosphorylating enzymes’ role in the regulation of gene expression involves what
protein activation
is acetylation of histone tains reversable
true
what is used to coordinate the expression of multiple related genes in eukaryotic cells
the genes share a common enhancer, which allows appropriate activators to turn on their transcription at the same time
how does a microRNA recognize a specific target mRNA
a microRNA can recognize a specific target wherever it can form complementary base pairs with the target
can mutations that occur in somatic cells be passed on to offspring
no
what separates during anaphase i
homologous chromosomes
crossing over contributes genetic variability between what
homologous chromosomes
what synthesizes short segments of RNA
primase
what covalently connects segments of DNA
ligase
which of the enzymes remove the RNA nucleotides from the priner and add equivalent DNA nucleotides to the 3’ end of Okazaki fragments
DNA polymerase I
Benzopyrene in cigarette smoke binds to DNA and distorts its shape, interfering with DNA replication. Which repair mechanism would most likely be used to repair the damage caused by this chemical
nucleotide excision repair
transcription of the structural genes in an inducible operon
starts when the pathway’s substrate is present
suppose an experimentser moves the operator to the far end of the operon, past the transacetylase (lacA) gene, what would likely occur when the cell is exposed to lactose
the structural genes will be transcribed continuously
for a repressible operon to be transcribed, what must occur
RNA polymerase must bind to the promoter, and the repressor must be inactive
in eukaryotes, general transcription factors do what
bind to other proteins or to a sequence element within the promoter called the tata box
what is used to coordinate the expression of multiple related genes in eukaryotic cells
a specific combo of control elements in each gene’s enhancer coordinates the simultaneous activation of the genes
what is a karyotype and what can it be used for
visual representation of an individuals complete set of chromosomes, allowing doctors to examine number and structure of chormosomes in cell to identify potential genetic abnormalities
what is meant by diploid and haploid
diploid has two complete sets of chromosomes, wchih is the case for most human body cells. haploid only has one set of chromosomes
what is aneuploidy
aneuploidy has only one extra or less chromosomes– partial set of chromosomes
what is polyploidy
extra complete sets of chromosomes
what are non-sister chromatids
belong to homologous chromosomes within a pair from differnt parents
how many alleles do you have for one gene
2
what is the difference between incomplete and codominance
incomplete is a mix, while codominance both appear together without blending
what is epistasis
expression of one gene is altered by the expression of one or more other genes
when more than one gene is responsible for a phenotype, the trait is said to be
polygenic
when one gene has multiple phenotypic effects it is called what
pleiotropty
what gene is responsible for sex determination
sry gene found on the y chromosome, means males who have the y chromosomes will develop male sex characteristics
what causes Hunington’s disease
mutation in the HTT gene- causes buiolding blocks of DNA to repeat many more times than they normally do
it’s hereditary
what causes down syndrom
trisomy 21- each cell has three copies of chromosome 21
what causes cru di chat
missing piece of chromosome 5- most cases occur in development of egg or sperm, but some cases occur when a parent passes a different, rearranged for of the chromosome to their child
what is amniocentesis
prenatal test by removing a small sample of amiotic fluid – can be used to diagnose chromosomal conditions, genetic disorders
Hersey/Chase experiment
labeled phage’s DNA with radioactive phosphorous and its protein coat with radioactive sulfur, Showed that the DNA represented the genetic material responsible for the inheritance of traits
what are the rungs of the helix are composed of
nitrogenous base pairs
the DNA backbone is held together by what type of bonds, and what carbons in the sugar are involved in these bonds
phosphodiester– covalent, 5’ carbon to 3’ caron
why is new dna synthesized in the 5’ to 3’ direction
the enzyme responsible for building the DNA chain (DNA polymerase) can only add new nucleotides to the 3’ hydrozyl group of the existing strand
What happens when a nucleotide is added to a growing strand of DNA? (What bonds are formed? Does it require ATP? What enzymes are needed?)
Phosphodiester bond formed between the nucleotide and growing strand of DNA, no— gets its energy from phosphate groups when breaking phosphate bonds within the nucleotide itself, needs DNA polymerase
what does primase do
enzyme that synthesizes RNA primers, which are short RNA sequences called primers
DNA polymerase I
in prokaryotic DNA replciation, support repair of damaged Dna, but also contributes to connecting Okazaki fragments
what does DNA polymerase III do
primary enxyme complex involved in the prokaryotic DNA replication- elongates DNA chains during bacterial chromosomal DNA replication
single stranded binding protein
binds to single strand of DNA near the replication fork
DNA ligase
enxyme that joins DNA strands together by forming phosphodiester bonds
how does DNA excision repair repair thymine dimers
Recognizes the distortion caused by the dimmer in the DNA helix, then cuts the DNA background on either size of the dimmer to excise the damaged section,, allowing a dna polymerase to fill in the gap with new nucleotides, finally sealing the nick with DNA ligase
Why is there an “end” problem with the lagging strand? What helps to protect the ends of the chromosomes? What enzyme is found in some cells to prevent this problem?
DNA polymerase can only add nucleotides in the 5’ to the 3’ direction, meaning it cannot fully replicate the very ends of the linear chromosomes on the lagging strand, leading to a gradual shortening with each replication cycle; telomeres are the protective structures at chromosomes end that prevent this issue, and the enzyme telomerase is found in some cells to extend these telomere res and counteract the shortening, thus preventing the loss of important genetic info.
At very end of chromosome, there isn’t enough space to add a primer for the last Okazaki fragment
What enzyme is responsible for synthesizing mRNA? In what direction does it synthesize the mRNA?
RNA polymerase synthesizes in 5’ to 3’ direction
What are the 3 stages of transcription?
initiation, elongation, and termination
what happens in initiation of transcription
binding of RNA polymerase and local unwinding of DNA
what happens in elongation stage of transcription
nucleotides are added to the 3’ end of the growing RNA strand
what happens during transcription termination
the newly synthesized RNA strand is released
what is the TATA box, and where is it found
found in promoter region of eukaryotes in the core promoter. it acts as a sgnal for where transcription should begin, usually around 25-30 base pairs upstream of the trascription start site, marks the location where RNA polymerase should bind
what is meant by 5’ UTR and 3’ UTR
untranslated regions of messenger RNA– influences mRNA stability and translation efficiency
what are splicesomes composed of
smll nuclear RNAs called small nuclear ribonucleoprotein particles (snRNPs)
what are 3 stages of translation
initiation, elongation, termination
initiation in translation
small subunit on mRNA binding site is joined by large subunit; aminoacyl tRNA binds
elongation of translation
ribosome moves along the mRNA extending the protein by shifting from peptidyl tRNA to aminoacyl tRNA
termination of translation
peptuide chain is released and ribosome dissociates from mRNA
what does aminoacyl-tRNA transferase do
attaches amino acids to tRNA molecules
what takes place at 3 different tRNA binding sites
enters at A, p is where polypeptide chain is attached to new amino acid, and E is where it exits
what is a polyribosome
cluster of ribosomes attached to a single mRNA molecule, allowing for the simultaneous tranlation of that mRNA into multiple protein copies, significantly increasing the protein synthesis within a cell
how is the translation of proteins destined for secretion different from those that will be used in teh cell
secreted proteins start their translation on the free ribosomes in the cytoplasm, but then are recognized by a signal sequence at their N-terminus, which directs the ribosome complex to the ER
what is meant by charging tRNA
process of attaching a specific amino acid to its corresponding tRNA molecule– basically activating the amino acid– aka amino acid activation
what is an operon
a group of genes that are transcibed together and controlled y a single promoter
describe the trp operon
cluster of genes in bacteria that code for enxymes necesary to synthesize the amino acid tryptophan, it is concered a repressible operon, it is turned on by default when tryptophan is needed and not readily available in teh environment.
regulated by trp represson
lac operon
— for using lactose instead of glucose— expresssed when lack of glucose, is inducible— only expressed when lactose is present
Usually turned off (repressed) but can be turned on
What effect does histone acetylation have on gene expression?
Histone acetylation activates gene expression — weaken the interaction between the histones and the negatively charged DNA, leading to a looser chromatin structure, so easier to promote transcription
what affect does methylation have on gene expression
slows or stops it
what role do transcription factors play in gene expression
Transcription factors are a broader category of proteins that bind to DNA to regulate gene expression,, including both activators and repressors.
Binds to dna to promote or inhibit the recruitment of RNA polymerase
what role do activators play in gene expression
Activators are proteins that bind to enhancer sequences on DNA— recruit other proteins like RNA polymerase complex to the promoter region, initiating transcription. Can be regulated by external signals, allowing for dynamic control of gene expression
what is a microRNA, and what does it do
Small, non-coding RNA molecule that plays a crucial role in regulating gene. Expression by binding to mRNA and inhibiting its translation into protein, effectively controlling the amount of specific protein produced within a cell
