DNA, RNA, Transcription and Translation Flashcards
What are genes made of?
A single DNA molecule exists as a double helix.
What is 1 DNA molecule made of?
2 polynucleotide chains, 2 strands, twisted clockwise around each other and are anti-parallel.
What are polynucleotides?
Chains of nucleotides: A,T,G,C,U.
How are 2 single-stranded DNA molecules held together?
By bonds between complimentary bases;
What is a nucleotide composed of?
Nitrogenous base + pentose + phosphate group
What are differences between DNA and RNA?
- DNA: the 5-carbon-sugar is deoxyribose (H-OH)
RNA: the 5 -carbon-sugar is ribose (OH-OH)
2.DNA: Thymine (with adenine)
RNA: Uracil (with adenine)
Define a phosphodiester linkage.
It is a link between the phosphate groups of 1 nucleotide and the hydroxyl group of another nucleotide to form a single-stranded DNA molecule.
Why are A and T complimentary bases?
- 2 hydrogen bonds
2. A is bigger (2 rings) and T is smaller (1 ring).
Why are C and G complimentary bases?
- 3 hydrogen bonds
2. G is bigger (2 rings) and C is smaller (1 ring).
What do genes do?
- Specify genetic information
- Control other genes
- Make RNA (transcription)
What are the types of RNA that play a role in protein synthesis?
rRNA (ribosomal), tRNA (transfer), mRNA (messenger)
What is the function of rRNA?
It combines with proteins to form proteins to form ribosomes. Nucleolus is the site of rRNA synthesis.
What is the function of tRNA?
It carries the amino acids used to synthesize proteins and brings them to the ribosome.
What is the function of mRNA?
It specifies the order of amino acids during protein synthesis.
What are other classes of proteins?
Protective, Regulatory, Enzymes, Motile, Structural, Storage, Transport.
What is transcription?
Using DNA as a template to make RNA (in other words, RNA synthesis)
What is transcribed?
- Only genes (start at promoter; end at terminator)
- 1 strand of DNA
Where are the new nucleotides added?
To the 3’ end of RNA (which is anti-parallel with DNA)
Describe the functions of RNA polymerase in transcription.
- unwinds ans separates ds DNA into ss
- reads DNA template (strand)
- adds RNA nucleotides (complimentary) to the 3’ end of the growing RNA.
- recognizes promoter and terminator (with help of transcription factors)
What is different in eukaryotic transcription that is not necessary in prokaryotic transcription?
- RNA polymerase needs transcription factors to find DNA and promoter/terminator
- 5’ cap added to 5’end of RNA
- Introns are removed from pre-mRNA to make mRNA
- Poly-A-tail is added to the 3’ end of RNA
Define 5’ cap.
A modified guanine that is added to protect RNA from breakage and to help transport RNA out of nucleus.
Define poly-A-tail.
Many adenine molecules.
True or False. Only mRNA can be translated?
True. pre-mRNA is made during transcription, but it needs to undergo RNA processing where the introns are removed + 5’ cap + poly-A-tail to make it mRNA and be translated.
During transcription, is the promoter transcribed?
No! Starts after the promoter.
What is translation?
Using mRNA as a template to make proteins comprised of amino acids (20).
Define codon.
A serie of 3 joined nucleotides that codes for an amino acid.
What does the ribosome do in translation?
- It holds and captures mRNA
- Reads mRNA from 5’ to 3’
- Translates 3 nucleotides into 1 amino acid.
Where does translation start and where does it end?
Start: AUG codon closest to 5’ end of mRNA
End: STOP codon (UAA, UAG, UGA)
Describe the initiation step.
- mRNA joins with ssu at 5’ end of untranslated region
- MET-tRNA attaches to start codon (AUG on mRNA)
- Lsu attaches and MET is at P site.
Describe the elongation step.
- Codon at A site recognized by anti-codon (tRNA)
- Peptide bond forms between aa at A and P site.
- Ribose moves forward on template and P moves to E.
Describe the termination step.
- STOP codon on mRNA at A-site is recognized
- Release factor fills A-site (no aa)
- Peptide chain is released and everything breaksdown into parts.
