Unit 3 - Molecular Genetics Flashcards
Chargaff’s Rule
Nucleotides are present in characteristic proportions;
In DNA, the percent composition of adenine (A) is the same as thymine (T), and that the percent composition of cytosine (C) is the same as guanine (G) (proportion of A=T and C=G)
Antiparallel Meaning
the two strands of nucleotides in DNA are opposite directions, one is oriented 5’ to 3’ and one is oriented 3’ to 5’
What phase of the cell cycle does DNA replication occur in?
Synthesis phase of Interphase
Explain the correct model of DNA replication (conservative, semi-conservative, or dispersive)
Semi-conservative: every new helix contains one old and one new strand, so it conserves half the strand of the original molecule
What are the three phases of DNA replication?
- Initiation: unwinding
- Elongation: complementary base pairing
- Termination: two new DNA molecules formed
Origin of Replication (definition)
Where replication begins
Helicase (function)
group of enzymes that unwind/unzip the double helix by breaking the hydrogen bonds between complementary bases
Single-stranded Binding Proteins (function)
stabilizes DNA during replication
Topoisomerase II (function)
enzyme that helps to relieve the strain/tension on the double helix sections ahead of replication forks/unwinding
Replication Forks (definition)
“Y-shaped” regions of replication bubble, direction of unwinding
DNA Polymerase III (function)
adds nucleotides to 3’ end of pre-existing chain of nucleotides, only builds in 3’ to 5’ direction
RNA Primase (function)
builds temporary RNA primers for DNA polymerase III to attach to begin elongation
Leading Strand (definition)
Continuously built strand, 3’ to 5’ template, built towards replication fork
Lagging Strand (definition)
Discontinuously built strand, in short fragments in opposite direction of leading strand, constantly needs more RNA primer as replication fork grows
Okazaki Fragments (definition)
Short fragments of DNA on lagging strand
DNA Polymerase I (function)
removes RNA primer, replacing it with correct DNA nucleotides. Also proofreads and fixes if needed
DNA Ligase (function)
joins Okazaki Fragments together
DNA Polymerase II
Proofreads DNA, if any mistakes it replaces it with the correct base
Telomeres (function, definition)
Repetitive sections of DNA near the end of each chromosome, to protect from loss of important genetic information during DNA replication. since the DNA at the ends of chromosomes cannot be copied fully.
Telomerase (function)
enzyme that extends the telomeres of chromosomes
Qualities of Genetic Code
- redundant, more than one codon can code for same A.A
- continuous, read as series of codons without spaces/punctuation
- nearly universal, almost every organism uses it other than some rare protists
Central Dogma of Genetics
genetic information is always going from DNA to RNA to Protein
Messenger RNA/mRNA (definition/function)
genetic messenger; copies a gene in the nucleus and provides information for protein synthesis in cytoplasm
Transfer RNA/tRNA (definition/function)
transfers the appropriate amino acid to the ribosome to build proteins
Ribosomal RNA/rRNA (definition/function)
structural component of ribosome, along with a protein it forms the ribosome which provides the construction site for polypeptide assembly
Steps of Protein Synthesis
Transcription: create complementary RNA strand of template strand
Translation: make polypeptide chain using genetic code
What does RNA Polymerase do?
Binds to promoter region of DNA and opens helix, binds to template strand, builds mRNA strand 5’ to 3’ that is complementary to the template strand of DNA, does not require a primer, once it reaches terminator sequence it dissociates with template strand and transcription is done.
What is the Promoter Region?
Upstream of a specific gene, mostly A’s and T’s since it takes less energy to break their bonds, tells RNA polymerase theres a gene nearby and to bind.
What is the Anti-Sense/Template Strand?
the strand of the DNA molecule that IS transcribed, starts at TAC written in the 3’ to 5’ direction
What is the Sense Strand?
strand of DNA that is NOT being transcribed
What is pre-mRNA?
precursor mRNA, only eukaryotes, mRNA before going through post-transcriptional modifications
What is a 5’ Cap and what is the purpose?
Post-transcriptional modification, modified G nucleotide is added to the 5’ end of the pre-mRNA to protect from digestion as it exits the nucleus
What is the Poly-A Tail and what is the purpose?
Post-transcriptional modification, a lot of A nucleotides are added to the 3’ end of pre-mRNA to keep it stable.
What are exons and introns? What is Splicing?
Exons: coding regions of eukaryotic DNA gene
Introns: non-coding regions of eukaryotic DNA gene
Splicing uses snRNA’s and proteins (snRNPs) and more proteins to form a splicesome that removes introns.
What is the Acceptor Stem of tRNA?
3’ end where amino acid attaches
What is an Anti-Codon on tRNA?
a complementary codon to a specific mRNA codon
Ribosomes (purpose, structure)
-provides site for protein synthesis to occur
-made up of rRNA and protein that form TWO subunits
-each ribosome has a binding site for mRNA and three for tRNA which permit the complementary base pairing between them
What is the universal START codon, what does it code for, and what is its function?
AUG
Codes for protein Methionine
Sets the reading frame for gene, the codons of mRNA that are read to produce the amino acid sequence, basically just starts the amino acid sequence
What are the 3 Binding Sites of Ribosome? Give brief explanation of each
P (peptide) site: where the tRNA with growing polypeptide is attached to it
A (amino acid) site: contains the tRNA with the next amino acid to be added
E (exit) site: uncharged tRNA is ejected
What bond are amino acids joined together by?
Peptide bonds
Define Mutation (single gene and chromosome)
Permanent change in the nucleotide sequence of a cell’s DNA.
Single gene: changes in nucleotide sequence of one gene
Chromosome: changes in chromosomes and may involve many genes
Point Mutation (definition)
Mutations of single base pair or small groups of base pairs
Substitution, insertion/deletion, inversion
Silent Mutation (definition)
mutation that does NOT change the amino acid sequence of a protein
Nonsense Mutation (definition)
mutation that shortens a protein by introducing a STOP codon
Missense Mutation (definition)
mutation that changes the amino acid sequence of a protein
conservative: A.A’s share same properties
non-conservative: A.A’s do not share same properties
Frameshift Mutation (definition)
inserting or deleting nucleotides not in a multiple of three as it shifts all the bases and alters the rest of the entire amino acid sequence
Gene Regulation (definition)
control the level of gene expression, either active, inactive, and its level of activity
Operon (definition, regions)
ONLY IN PROKARYOTES; cluster of genes (2+) under the control of a single promoter
Two regions:
-Regulatory region containing operator and promoter -Coding region: location of genes that will get transcribed
Operator (function)
In regulatory region of operon, the binding site for a repressor protein
Repressor Protein (function)
In regulatory region of operon, inhibits the initiation of transcription
Activator Protein (function)
can enhance levels of transcription even more
