Lecture 8-9: Genes, Gene Expression and Mutations Flashcards
chromatin
DNA in eukaryotic cells is bound to special proteins that act as spools, condensing and protecting the DNA molecule
DNA + Protein = chromatin
what are the proteins associated with DNA (for chromatin) called?
histones
when i chromatin seen
when the cell is not dividing
name the types of chromatin in eukaryotic cells
- euchromatin
- heterochromatin
euchromatin
not easily visible, loose chromatin that is found throughout the nucleus
- loose lightly packed chromatin
- rich in genes
- comprises the most active portion of the genome of any given cell (gene expression)
heterochromatin
- tightly packed DNA when the cell is not dividing
- represents the inactive portion of the genome. genes are silenced (no gene expression)
chromosomes (when formed… of what)
when a cell is ready to divide, the chromatin is tightly packaged nd condensed to form chromosomes
how many pairs of chromosomes do humans have
23 pairs
genes
discrete unit of the hereditary information consisting of a specific nucleotide sequence in DNA
always located on a specific location (gene locus)
gene locus
specififc location where genes are always located
how does DNA lead to specific traits
by dictating the synthesis of proteins
every gene is like a recipe for a single product, a single polypeptide
genome
the genetic material of an organism or virus; the complete complement of an organism’s genes along with its noncoding nucleic acid sequences
is number of genes related to genome size
no
who has lowest gene density. why?
humans and other mammals due to large amount of non-coding DNA between genes
telomeres
- when eukaryotic ells divide, the chromosomes get shorter bc the ends are not fully replicates
- to protect genes of eukaryotic cells from being eroded, non-coding DNA sequences at their ends are called telomeres
telomeres are a repetition of which nucleotide sequence. repeated how many times
TTAGGG
100-1000 times
telomerase
germ cells have an enzyme called telomerase that catalyzes the lengthening of telomeres in eukaryotic germ cells
gene expression
what are the stages?
process by which DNA directs the synthesis of proteins
- transcription
- translation
triplet code
genetic instructions for a polypeptide chain are coded as a series of non-overlapping, three nucleotide
transcription
DNA -> RNA
genetic information in the form of DNA is used as a template to generate a molecule of RNA
stages of transcription
- initiation
- elongation
- termination
RNA polymerase function
- binds to a specific gene region on the chromosome
- separates double helix at a specific gene region
- DNA read form 3’-5’ and transcribed into messenger rna
- transcription occurs 5’-3’
- mrna strand is complementary to DNA
transcriotion - initiation
RNA polymerase binds to teh DNA molecule and splits the double helix
transcription - elongation
RNA polymerase reads the 3’-5’ DNA strand
RNA polymerase synthesizes a mRNA strand from 5’-3’
the mRNA strand is the compliment to the DNA template (strand it reads)
transcription termination
RNA polymerase reaches the end of the gene and detaches
DNA double helix reforms
mRNA leaved the nulceus
template strand
the strand of DNA that is transcribed
coding strand
the strand of DNA that is NOT transcribed
are the template and coding strands complementary?
yes
Translation
RNA -> proteins
codons
triplet code found on mRNA
tRNA
each tRNA molecule has a 3D conformation due to stretches of complimentary bases
- contain anticodon: nucleotide triplet which base pairs with a complimentary codon of the mRNA
- at the other end of the tRNA molecule is a bonding site for a specific amino acid
ribosomes - translation
made of 2 subunits: large and small subunit composed of proteins and rRNA molecules
- where the synthesis of polypeptide occurs
- facilitate the specific coupling of tRNA anticodons with mRNA codons by holding tRNA and mRNA close together, enabling the addition of amino acids to the growing polypeptide chain
translation initiation full steps
- small ribosomal subunit binds to mRNA
it scans the mRNA for the start codon (AUG) and binds to the mRNA at that location - the initiator tRNA binds to the mRNA at start codon
the initiator tRNA carries the anti-codon UAC which is complementary to the start codon (AUG) - large ribosomal subunit binds
the binding of the large subunit requires energy
translation steps (names)
- codon recognition
- peptide bond formation
- translocation
translation - codon recognition
the anticodon of an incoming aminoacyl tRNA base pairs with the complimentary tRNA base pairs with the complementary mRNA codon A site
translation - peptide bond formation
a peptide bonds is formed between the new amino acid at the A site and the growing polypeptide at the P site; this step attaches the polypeptide to the tRNA at the A site
translation – translocation
ribosome translocates the tRNA in the A site to the P site
the mRNA is moved through the ribosome (it is not the ribosome that is moving along the mRNA) 5’ end first
empty tRNA in the P site is moved to the E site, where it is released; the mRNA moves along with its bouns tRNA’s, bringing the next codon to be translated into the A site
translation termination
elongation occurs until the stop codon arrives at the A site
a protein called a release factor binds to the A site
what are mutations
changes in the nucleotide sequence of an organism’s DNA
they are responsible for the huge diversity of genes fund among organisms because mutation are the ultimate source of new genes
small scale mutations
point mutations: changes in a single nucleotide pair of a gene
- if it occurs in a gamete or cell that gives rise to gametes, it may be transmitted to offspring
- if the mutation has an adverse effect on the phenotype of an organism, the mutant condition may be referred to as a genetic disorder or hereditary disease
base pair substituions (nucleotide-pair substitution, silent mutations)
- nucleotide-pair substitution: replacement of one nucleotide and its partner with another pair of nucleotides
- silent mutations: base-pair substitution that has no effect on the coded protein owing to the redundancy of the genetic code
missense mutations
base pair substitutions that change one amino acid to another
such a mutation may have little effect on the protein:
- new amino acid may have similar properties as the one it replaces
- new amino acid may be in a region of the protein where the exact sequence of amino acids is not essential to function
nonsense mutations
- base pair substitutions that change one amino acid into a stop codon
- causes translation to be terminated prematurely
resulting polypeptide will be shorter - nearly all nonsense mutations lead to nonfunctional proteins
insertion and deletions
additions or losses of nucleotide pairs in a gene
- causes translation to be terminated prematurely: have disastrous effect on the resulting protein more often than substitutions do
frameshift mutation
when an insertion or deletion alters the reading frame of the genetic message, the triplet grouping of nucleotides on mRNA that is read during translation
what mutation
ACU to ACC
(thr to thr)
silent
what mutation
CAU to CAA
len to gln
missense
what mutation
UGC to UGA
UGA = stop
nonsense
