Chapter 10 Flashcards
Genetic Material
bacteriophages
(phages) viruses that exclusively infect bacteria
bacteriophage replication steps:
1) phage attaches to a bacterial cell wall
2) phage injects own DNA into bacterial cell
3) phage DNA directs bacterial cell to make more phage DNA / protein; assemble new phages
4) cell lyses and new phages are released
monomer of DNA / RNA
nucleotides
polymer of nucleotides ?
DNA / RNA
polynucleotide
polymer of many nucleotide monomers covalently bonded together
DNA
double-stranded helical nucleic acid molecule
what makes up DNA ?
- nitrogenous base (A / T & G / C)
- phosphate group
- deoxyribose sugar
what makes up RNA ?
- nitrogenous base (A / U & G / C)
- phosphate group
- ribose sugar
pyrimidines
1 ring nitrogenous base
- T / C / U
purines
2 ring nitrogenous base
- A / G
nucleotide
building block of nucleic acids
- 1 phosphate group, 1 5C sugar, nitrogenous base
sugar-phosphate backbone
alternating chain of 5C sugar and phosphate group where nitrogenous base attaches to
how does the nitrogenous base connect to the phosphate-sugar backbone ?
bonding w/ the 5C sugar
double helix
DNA structure;
- two DNA strands interwound together in helical shape
how many hydrogen bonds hold together G / C ?
functional groups form 3 hydrogen bonds
how many hydrogen bonds hold together A / T ?
functional groups form 2 hydrogen bonds
orientation of the 2 DNA strands ?
antiparallel; one runs one way while other runs opposite way
5’ ——— 3’
3’ ——— 5’
5’ end of single DNA strand holds what ?
phosphate group
3’ end of single DNA strand holds what ?
OH
what model showed the helical structure of DNA ?
watson-crick model
- rosalind franklin contributed a lot
what main point does watson-crick model suggest ?
molecular explanation for genetic inheritance
complimentary DNA sequence of GGCATAGGT ?
CCGTATCCA
primary function of DNA ?
encode / store genetic info
- molecular basis of heredity
how does DNA strands replicate ?
original helix strands unravel and 2 new strands are made to wind with 2 original template strands
- new strands lay down coinciding base pairs to original template strands
- 1 helix becomes 2 helixes
semiconservative model
type of DNA replication in where new replicated helix consists of new strand one original template strand from original helix
how does complimentary base pairing make DNA replication possible ?
free nucleotides can form a new strand by bonding w/ their base pair along the original template strand
- synthesizes a new DNA strand
where does DNA replication start on the original DNA strand ?
sites called origins of replication
- short strands of specific nucleotide sequences
what direction does DNA replication go ?
goes out from either side of origin of replication
- forms replication bubble
why is there many origins of replication and in-turn, many replication bubbles in eukaryotic chromosomes ?
lessens time to fully replicate DNA strand
DNA polymerase
assembles DNA nucleotides using template DNA strand to form new DNA strand
- proofreads all nucleotides placed down; removes any base-paired incorrectly
what direction will DNA polymerase lay down nucleotides ?
5’ —> 3’
- can only lay down nucleotides on the 3’ end
how does DNA polymerase lay down nucleotides on DNA strand 3’ —> 5’ ?
lays down nucleotides in 5’ —> 3’ direction in sections
- okazaki fragments
strand that is synthesized by DNA polymerase leading in 5’ —> 3’ direction ?
leading strand
- continuous synthesize
- synthesize toward forking point
strand that is synthesized by DNA polymerase leading in 3’ —> 5’ direction ?
lagging strand
- fragment synthesis
- synthesize out from forking point
DNA ligase
enzyme that joins together okazaki fragments on lagging strand to make one continuous DNA strand
how can DNA strands be harmed ?
- ultraviolet light
- x-rays
- toxic chemicals (tobacco)
how are DNA strands repaired ?
by DNA polymerase / ligase
transcription
synthesis of DNA —> RNA
- in nucleus
hows does transcription work ?
essentially just DNA replication using A/U
& G/C nucleotide pairs
- uses a single DNA strand from unraveled helix and makes 1 RNA strand
initiation of transcription
RNA polymerase attaches to promoter and starts RNA synthesis
elongation of transcription
RNA polymerase continues to elongate RNA strand using DNA template
termination of transcription
RNA reaches terminator DNA
- RNA polymerase detaches from RNA strand
translation
synthesis of RNA —> proteins
- in cytoplasm
how does translation work?
3 RNA nucleotides make up a codon
- specific codon translates into specific amino acid
codon
3 nucleotides sequence in mRNA
- basic unit of genetic code
what is the minimum # of nucleotides to code for polypeptide 100 amino acids long ?
300 nucleotides
genetic code
set of rules that dictate amino acid translation of each mRNA nucleotide triplet
RNA polymerase
transcription enzyme;
- links together RNA nucleotides during transcription
- opens DNA helix and uses 1 strand as template
promoter
binding site of RNA polymerase;
- where transcription begins
- specific nucleotide sequence in DNA
terminator
signals RNA polymerase to release formed RNA strand and depart from gene
- special DNA sequence showing end of gene
messenger RNA (mRNA)
type of RNA that encodes genetic info and conveys it to the ribosomes
- ribosomes translate info into amino acid sequence
how is mRNA modified before leaving the nucleus in eukaryotic organisms ?
- small cap of modified G nucleotides at 5’ end
- large cap of (50-250) A nucleotides at 3’ end
caps are NOT translated into proteins
what is the point of modifying mRNA w/ caps at both 5’ / 3’ end before leaving the nucleus ?
- facilitate export
- protect from degradation
- help ribosomes bind to mRNA strand
introns
noncoding region of RNA from DNA that will not be translated into proteins
- removed from mRNA strand before leaving nucleus
exons
part of a gene that will be expressed and translated into proteins
- exons will join together before leaving nucleus to form continuous mRNA strand
RNA splicing
removal of introns and joining of exons before mRNA leaves nucleus
- forms continuous mRNA strand
why are most eukaryotic genes longer than the mRNA that leaves the nucleus ?
because of RNA splicing, intron portions are removed from strand while exons are kept
transfer RNA (tRNA)
type of RNA
- pick up specific amino acid
- lay amino acid to specific codon on mRNA
anticodon
on tRNA, 3 nucleotide sequence complimentary to codon tiplet on mRNA
- how amino acid knows where to lay amino acid
- opposite side of amino acid attachment side
how are amino acids attached to tRNA ?
by a enzyme for each specific amino acid
where does the formation for the amino acid polypeptide chain by tRNA in accordance to mRNA strand occur ?
in the ribosome
ribosomes
cell structure of RNA and proteins
- site of protein synthesis
- 1 large subunit / 1 small subunit
ribosomal RNA (rRNA)
type of RNA w/ proteins that make up ribosomes
- most abundant RNA in most cells
where does mRNA bind on a ribosome ?
the small subunit
where does tRNA bind on a ribosome
the large subunit
- P / A site
how does a ribosome facilitate protein synthesis ?
ribosome holds together mRNA / tRNA together
- connects amino acids from tRNA to growing polypeptide chain according to mRNA
three phases of transcription / translation:
1) initiation
2) elongation
3) termination
initiation of translation
1) mRNA binds to small subunit of ribosome via start codon
2) large subunit of ribosome binds to small making functioning ribosome
- initiator tRNA fits into tRNA binding site (P site) on ribosome
start codon
on mRNA, 3 nucleotide sequence (AUG) where initiator tRNA binds
- starting translation
P site
ribosome binding site where initiator tRNA binds
- holds tRNA carrying polypeptide chain
A site
(aminoacyl tRNA) one of ribosome’s binding site
- holds the tRNA that carries the next amino acid of polypeptide chain
what would happen if a genetic mutation in a gene changed a start codon to some other codon ?
mRNA transcribed from mutated gene would not work because ribosomes cannot start translation correctly
elongation of transcription
1) anticodon of incoming tRNA carrying amino acids in A site of ribosome
2) polypeptide chain separates from tRNA in P site and attaches to amino acid of tRNA in A site
3) P site tRNA leaves site, ribosome moves A site tRNA w/ polypeptide chain to now empty P site
repeats
termination of transcription
stop codon stops protein synthesis;
- one of 3, 3 nucleotide codons that signal gene to stop
- polypeptide is released from last tRNA and ribosome subunits separate
the 3 stop codons
- UAA
- UAG
- UGA
what would happen if a mutation caused a codon in the middle of the mRNA to be a stop codon ?
translation will end prematurely
which type of nucleic acid does not directly participate in translation ?
DNA
mutation
change in genetic information of cell
mutagen
chemical / physical agent that interacts w/ DNA and causes mutation
how could a single nucleotide substitution result in a shortened polypeptide ?
substitution that changes a codon to now code for a stop codon
- ending polypeptide chain prematurely
one gene one enzyme hypothesis
each gene produces a specific polypeptide
- polypeptide may function as an enzyme / subunit of an enzyme
