Chapter 17 Flashcards
What are genes?
Sequences of DNA that encode for proteins and how much protein should be made
What are mutations?
They occur in genes and introduce variation ; can form new alleles
What does Polygenic mean?
A characteristic that is influenced by two or more genes
What does epistasis mean?
Interactions between genes
Interactions between genes and the environment
Multifactorial
what does Epigenetics mean?
Behaviors and environment can cause changes that affect the way your genes are expressed
What is transcription?
Information from a DNA sequence is copied to a complementary RNA sequence
What is translation?
Converts the RNA sequence to an amino acid sequence
What does DNA polymerase do?
It pries the DNA strands apart and adds RNA nucleotides ; doesn’t need a primer
3 stages of transcription
Initiation, elongation, termination
What do transcription factors do?
They mediate the binding of RNA polymerase and the initiation of transcription
What is the transcription initiation complex made up of?
Transcription factors, RNA polymerase II, and a promoter
What does RNA polymerase do in initiation?
It binds to the promoter, unwinds the DNA strands and initiates RNA synthesis at the start point on the template strand
What does RNA polymerase do in elongation?
It adds nucleotides to the 3’ end of the growing strand in an anti parallel fashion
What does the terminator do in termination?
It causes the RNA pol to detach from DNA and release the transcript
Prokaryotic transcription
Transcription and translation occurs in the same physical space (no nucleus) ; mRNA that is made is directly translated into protein sequence
Eukaryotic processing of mRNA
Transcription and translation ; mRNA needs to leave nucleus to be translated ; enzymes modify pre-mRNA before the genetic messages are dispatched to cytoplasm
Functions of the 5’ cap
Protects transcript from being broken down ; helps ribosomes attach to 5’ end of mRNA
Functions of the poly-A tail
Facilitate the export of transcript from the nucleus to cytoplasm ; helps to make the transcript more stable
What are coding and noncoding sequences called?
Coding sequences are called exons and noncoding sequences are called introns
What happens if introns are not removed?
The noncoding sequences would be translated resulting in a non-functional protein
What is alternative RNA splicing?
Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing
Transfer RNA
tRNA enables translation of a given mRNA codon into a certain amino acid
Codon
Sequential 3-letter “words” (3 bases)
The genetic code is ____ but not ____
Redundant ; ambiguous
Start codon
AUG ; methionine
Stop codons
UAA ; UAG ; UGA
tRNA binding sites
P site ; A site ; E site
P site
Peptidyl-tRNA ; Holds the tRNA carry the growing polypeptide chain
A site
Aminoacyl ; Holds the tRNA with the next amino acid to, be added to the chain
E site
Exit ; releases the tRNAs from the ribosome
Two instances of molecular recognition for accurate translation
Correct match between tRNA and an amino acid , done by the enzyme aminoacyl-tRNA synthetase ; correct match between tRNA anticodon and mRNA codon
What is wobble?
Flexible pairing at the third base of a codon ; allows some tRNAs to bind to more than one codon;
Three stages of translation
Initiation, elongation, termination
Initiation of translation
AUG begins the formation of an initiation complex ; put together by initiation factors
Elongation
Codon recognition, peptide bond formation, translocation
Codon recognition of elongation
Anticodon of an incoming tRNA base pairs with the mRNA codon in site A
Peptide bond formation in elongation
Catalyzed by the large ribosome subunit between amino groups of a new amino acid in site A and the Carboxyl end of the growing peptide chain in site P
Translocation in elongation
Ribosome translocation the tRNA in site A to site P, at the same time the empty tRNA in P is moved to the E site where it is released
Termination
When ribosome becomes filled with stop codons ; no tRNAs that complement those codons
Nuclear localization signal (NLS)
Targets the protein to the nucleus
What happens when a polypeptide has a signal directing it to the enough ER?
Translation will pause, and the ribosome will bind to a receptor at the RER membrane when elongation continues
Different post-translational modifications
Proteolysis, glycosylation, phosphorylation
What is proteolysis?
Cutting off signal sequences or cutting a long chain into final products by proteases
What is glycosylation?
Addition of carbohydrates to for, glycoproteins
Somatic mutations
Occur in nongermiline tissues ; can’t be inherited
Germline mutations
Present in egg or sperm ; can be inherited ; cause cancer family syndrome
Silent mutations
Have no effect on the amino acid produced by a codon
Missense mutations
Still code for an amino acid, but not the correct amino acid
Nonsense mutations
Change an amino acid codon into a stop codon ; most lead to a nonfunctional protein
What are insertions and deletions?
Additions or losses of nucleotide pairs in a gene
