Unit 5 Flashcards
What is Chargaff’s rule?
The number of A=T and the number of G=C
How many origins of replication can eukaryotes have?
hundreds or thousands
What is the replication fork?
a Y-shaped region where parental DNA strands are unwound
What are helicases?
enzyme that untwists the double helix at the replication fork
What is topoisomerase?
an enzyme that relieves strain of the DNA untwisting
What does DNA polymerase do?
makes new DNA at the replication fork?
What is the difference between the leading and the lagging strand?
the leading strand is continuously built toward the replication fork, but the lagging strand works in small sections away from the replication form in pieces called Okazaki fragments
What else does DNA polymerase do?
proofread newly made DNA
What happens in mismatch repair?
repair enzymes replace incorrectly paired nucleotides
What do telomeres do?
they postpone the erosion of genes near the ends of DNA molecules
Where does transcription occur in a eukaryotic cell?
the nucleus
Where does translation take place in a eukaryotic cell?
cytoplasm
What is the first stage of gene expression?
transcription
What is a promotor?
what initiates transcription
What are transcription factors?
proteins that help control the rate of transcription by turning on and off genes
What are the three stages of transcription?
initiation, elongation, termination
What are introns?
noncoding segments
What are exons?
a coding region of DNA that is eventually expressed
How can a gene encode more than one kind of polypeptides?
by changing which segments are introns and exons (this is called RNA splicing)
What does tRNA do?
It carries specific amino acids and the anticodonmust bind to the codons of the mRNA.
How does accurate translation occur?
a correct match between a tRNA and an amino acid and a correct match between the tRNA anticodon and an mRNA codon
What do free ribosomes synthesize?
proteins that function in the cytosol
What do bound ribosomes do?
make proteins of the membrane system and proteins that are secreted from the cell
Can ribosomes switch from free to bound?
yes because they are identical
What is a polyribosome?
when multiple ribosomes can translate a single mRNA simultaneously so that multiple copies can be made at once
What are the three types of nucleotide pair substitutions?
silent, missense, nonsense
What is missense?
when a substitution causes the sequence to code for a different amino acid
What is nonsense?
a substitution that leads to a stop codon
What is a frameshift mutation?
when an insertion or deletion causes the reading frame to be altered
What are mutagens?
physical or chemical agents that cause mutations
What is an inducible operon?
an operon that is usually off until an inducer activates the repressor and turns on transcription (think about lactose example)
When do inducible enzymes usually function?
catabolic pathways and they are induced by a chemical signal
When do repressible enzymes usually function?
anabolic pathways and their production is repressed by a high level of the end product
Why is gene expression regulation important?
almost all cells in an organism contain the same genes but not all the genes need to be on all the time
Where is gene repression most often regulated?
translation
What does histone acetylation do?
opens chromatin and regulates structure
