Unit 6 Flashcards
What does “antiparallel” mean?
The subunits/backbones run in opposite directions.
What are the structural differences between DNA in prokaryotes and eukaryotes?
Prokaryotes → double-stranded circular DNA molecules with a small amount of proteins
Eukaryotes → linear DNA molecules with a large amount of proteins
What are the base pairing rules and how does it differ between DNA and RNA?
Adenine and thymine
Guanine and cytosine
In RNA, thymine is replaced with uracil
What is a helicase?
Enzymes that untwist the double helix at the replication forks
What does DNA polymerase do?
Catalyze the synthesis of new DNA at the replication fork
What does topoisomerase do?
Relieves the strain of twisting the double helix by breaking/swiveling/rejoining DNA strands
What does ligase do?
The segments created in the lagging strand are joined together by DNA ligase
What direction is DNA synthesized?
5’ to 3’ end. Nucleotides can only be added to the 3’ end of a strand.
What is meant by DNA replication being semi-conservative?
Each daughter molecule will have one old strand and one new strand
What is the leading strand?
DNA polymerase creates a leading strand when it continuously synthesizes toward the replication fork
What is the lagging strand?
To create the lagging strand the DNA polymerase must work away from the replication fork. It is synthesized as a series of segments which are joined by ligase
How is transcription different in prokaryotes and eukaryotes?
Prokaryotic transcription takes place in the cytoplasm while eukaryotic transcription takes place in the nucleus
What does the RNA polymerase do?
Pries apart the DNA strands and joins together the RNA nucleotides
How do new nucleotides match up to form the new mRNA strand?
Complementary base pairing
What direction is the mRNA synthesized?
5’ to 3’ direction
What is the difference between the template and coding strand of DNA?
Template strand is one of the strands of DNA that provides a template for the creation of the coding strand
What kind of cell does RNA processing occur in?
Eukaryotic
When does RNA processing take place?
After transcription and before translation
Where does RNA processing take place?
The nucleus
What is added to the ends of the mRNA molecule?
5’ end → modified nucleotide 5’ cap
3’ end → poly-A tail
What is an intron?
Noncoding segments in a gene (introns are in the way)
What is an exon?
Regions that are expressed, translated into amino acid sequences (exons are expressed)
What do spliceosomes do?
Catalyze the splicing reactions
What is alternative splicing?
Some genes can encode more than one kind of polypeptide depending on which segments are treated as exons during splicing
How is translation different in prokaryotes and eukaryotes?
Prokaryotes → translation can begin before transcription is finished
Eukaryotes → the nuclear envelope separates the two processes
What is the difference between codons and anticodons?
Codons are on mRNA, anticodons are on tRNA
They are complementary and bind to each other to create the amino acid chain
What is the structure of tRNA?
- Consists of a single RNA strand that twists into a 3D shape due to hydrogen bonding
- Roughly L shaped with 5’ and 3’ ends located near one end of the structure
- 3’ end is an attachment site for an amino acid
What does tRNA do?
Enables translation of a given mRNA codon into an amino acid
Where is rRNA found?
Within the ribosomes
What does rRNA do?
Helps form ribosomes
What are the three phases of translation?
Initiation, elongation, termination
What triggers initiation?
A start codon
What is elongation?
The matching of mRNA codons and tRNA anticodons to bring in amino acids
What triggers termination?
A stop codon
What are regulatory sequences?
Sections of DNA that can help control transcription by interacting with regulatory proteins
What are epigenetic changes?
Reversible modifications of DNA or histones
What is methylation?
The addition of methyl groups so that DNA is more tightly packed around the histones and can’t be transcribed
What is acetylation?
The addition of acetyl groups to open up the chromatin structure, promoting the initiation of transcription
Are epigenetic changes heritable?
For epigenetic changes to be heritable they must occur in the organism’s gamete
What are promoters?
Sections of DNA found before the gene where RNA polymerase and transcription factors bind to start transcription
What are negative regulatory molecules?
They bind to DNA to block transcription and inhibit gene expression
What do small RNA molecules do
Regulate gene expression by binding to mRNA so that it cannot be translated by ribosomes or is marked to be broken down
What are operons?
Groups of related genes transcribed together into a single mRNA, typically in prokaryotes
What do eukaryotes use for gene regulation?
Specific transcription factors, activators, enhancers, mediator proteins
What does electrophoresis do
Separates molecules (alleles) according to size
What does PCR do?
Replicates DNA fragments
What does bacterial transformation do?
Inserts new DNA into bacterial cells
What does DNA sequencing do
Determines the order of nucleotides in a strand of DNA
What are the types of mutations?
Substitutions, insertions or deletions (frame shift mutations)
Silent (no effect, codes for the same amino acid), missense (codes for different amino acid), nonsense (changes an amino acid into a stop codon)
How are genes regulated in prokaryotes?
The operon can be switched on or off by a repressor
A corepressor binds to the repressor to switch off an operon
An inducer binds to the repressor to switch on an operon
