DNA (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 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
What is meant by DNA replication being semi-conservative?
Each daughter molecule will have one old strand and one new strand
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
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 direction is the mRNA synthesized?
5’ to 3’ direction
How do new nucleotides match up to form the new mRNA strand?
Complementary base pairing
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
