Unit 4: Molecular Biology Flashcards
What is a nucleotide?
A subunit of DNA that consists of a nitrogenous base attached to a deoxyribose sugar, which is connected to a phosphate group
What is the type of bond that is formed between the nitrogenous bases?
- Thymine and adenine form 2 hydrogen bonds
- Cytosine and guanine form 3 hydrogen bonds
What type of bond holds the base pair to the sugar backbone and what type of bond holds the sugar to the phosphate?
A glycosyl bond holds the base pair to the sugar backbone.
A phosphodiester bond holds the sugar to the phosphate.
Step by step explanation of DNA replication
- gyrate relaxes twisted DNA
- helicase “unzips”; breaks hydrogen bonds
- SSBP attach to prevent annealing
- RNA “hooks” laid down by RNA primase
- DNA polymerase III builds new complementary strand
- DNA polymerase I removes RNA primers and replaces them with DNA
- ligase connects fragments
transcription: purpose and location
DNA is used as a template for the production of a complementary strand of mRNA that can leave the nucleus; occurs in the nucleus
translation
ribosomes assemble proteins from amino acids by “reading” the mRNA
List and describe the 3 stages of transcription.
Initiation: RNA polymerase binds to the beginning of the section of DNA to be copied and unwinds it
Elongation: either single strand of DNA acts as a template for complementary bases to make mRNA
Termination: mRNA is released when the gene is completed - this is recognized by a terminator sequence
What is the purpose of the promotor region/TATA box?
to allow enzymes (specifically RNA polymerase) to locate a certain gene
What purpose do telomeres serve?
Telomeres are noncoding sequences of DNA at the ends that prevent important DNA from being destroyed due to DNA replication
What is the Hayflick limit?
the number of times a cell can divide before its telomeres have been lost
What was the Meselson Stahl Experiment?
- experiment that proved DNA replication is semi-conservative by growing bacteria in heavy nitrogen and normal/light nitrogen
- after one round of growing heavy nitrogen DNA in light nitrogen, the DNA had density of hybrid
- proved that each original strand was a template for a new strand
What are 2 types of DNA repair mechanisms?
Direct Repair - DNA polymerase II checks to make sure the correct base has been paired; errors corrected even before strand is replicated
Excision Repair - whole chunk of DNA is removed by enzymes
List and describe the 3 base substitution/point mutations.
- Misense mutation: single changed base causes a different amino acid to be added to the protein (e.g. hemophilia)
- Nonsense mutation: single base change codes for STOP in the middle of the protein
- Silent mutation: single base change that still codes for the same amino acid (no effect, no problem)
What is an insertion/deletion mutation (+ another name for it)
when a base is added or removed (frameshift mutation) (e.g. Huntington’s Disease)
What are tRNA?
transfer RNA; delivers amino acids to ribosomes; on one arm has a sequence of 3 bases called an anticodon, which allows the complementary mRNA to recognize it (that is how the mRNA is read to assemble certain amino acids and create protein)
