Unit 2 Flashcards
(42 cards)
What are DNA molecules comprised of?
thousands of nucleotides joined together in a chain by their phosphate groups
What are nucleotides comprised of?
base + deoxyribose sugar + phosphate
What are the 4 types of bases?
– two purines; double ring (adenine and guanine)
– two pyrimidines; single ring (thymine and cytosine)
Describe the composition of a DNA strand.
DNA: double helix nucleotide chains held together by
hydrogen bonds between adenine and thymine (2) and
between guanine and cytosine (3)
* twisted ladder with the bases forming the steps and the
deoxyribose-phosphate forming the two sides of the
ladder
* two strands are not identical but complementary
Replication is ______ to _______.
DNA to DNA
Describe the process of replication.
Replication (DNA→ DNA)
* DNA replication: hydrogen bonds between bases broken
* Each single strand has the information to make a new
complementary strand;
– T in the original strand, an A will be placed opposite it in the new
strand
* Many enzymes and cofactors required.
* Replication starts at a specific sequence called an origin of
replication,
* Helicase enzymes break the hydrogen bonds between bases
* DNA polymerases synthesize the new strand recognizing
each base and attaching the correct complementary base
Describe the repair process and when it is required.
- Errors
– Mistakes sometimes during replication
– chemicals and UV light - If the damage is not repaired
– change in DNA (a mutation) may be passed on to other cells. Can
be good or bad - Several enzymes work to repair damage:
– DNA polymerases can reverse themselves and go back to repair
damage during replication;
– DNA repair nucleases can cut out damaged pieces of DNA and then
put in the correct bases;
– DNA ligase connects the repaired section to the main strand.
Describe DNA genetic code
- 4 bases in DNA (ACGT) → 20 amino acids
- code is triplet: a sequence of 3 nucleotides
codon) along the DNA strand calls for
particular amino acid - Gene: the linear sequence of nucleotides in
DNA that designates all the amino acids in a protein or polypeptide chain
What are the 3 types of RNA?
– messenger RNA (mRNA)
– ribosomal RNA (rRNA)
– transfer RNA (tRNA)
Describe the structure of RNA.
- Structure
– Nucleotides (base + ribose sugar + phosphate) joined
together in a chain by their phosphate groups (similar
to DNA)
– RNA Nucleotides: same bases as found in DNA
except uracil replaces thymine
– RNA molecules are single stranded
– some parts of RNA molecules may be folded to have
sections that are double stranded
Describe DNA to RNA transcription.
DNA to RNA
* mRNA synthesized by copying one strand of
DNA in a complementary fashion;
* RNA polymerases attach at a promoter region on
DNA
* Open up the DNA double helix
* Add complementary nucleotides and connect to
make an RNA
* Carries the genetic instructions to the cytoplasm
where protein synthesis occurs
Describe DNA to mRNA transcription.
- In eukaryotes, mRNA must be processed before
leaving the nucleus - Introns (sequences that do not code for protein) are
cut out - Exons (code for protein) remain
- To prevent degradation by RNAses in the cytoplasm
– Cap is added at one end
– Tail of adenine bases is added at the other end
Given the following strand of DNA, what would be the sequence of the mRNA made during transcription ?
* TAC AAA ACT
ATG TTT TGA
Translation is _____ to ______.
RNA to protein
Describe the whole process of translation (this is all of the information).
Genetic code:
* Triplet/codon: a sequence of 3 nucleotides along
the DNA strand calls for particular amino acid
* Redundant: more than one codon for most amino
acids
* one start codon: only codon designating the
amino acid methionine
* 3 stop codons
- Ribosomes made of protein and RNA (rRNA)
- Two subunits:
– a smaller one with a binding site for mRNA
– larger one with 3 binding sites for tRNAs. - tRNAs (adaptor)
– Different tRNA for each codon – each is folded in a
characteristic way with stems and loops
– One of the free ends of the tRNA has an attachment site for an
amino acid
– Specific enzyme (aminoacyl-tRNA synthetase) recognizes the
shape of the tRNA and attaches the correct amino acid
– In the loop opposite the free ends, 3 bases anticodon:
– complementary to the codon for the amino acid that is attached
to the tRNA - Initiation
– Initiator tRNA (methionine) and mRNA
attach to the small ribosomal subunit - anticodon of the tRNA attaches to the start codon
on mRNA
– The larger ribosomal subunit attaches to the
smaller subunit - Elongation
– tRNAs with amino acids attach to ribosome
and to the mRNA codons complementary to
the tRNA anticodons.
A site = Aminoacyl-tRNA receiving site
– Peptide bonds are formed between the amino
acids, and the ribosome moves down the
mRNA. - Termination
– At stop codon
– a cytoplasmic protein binds to the mRNA
– ribosomal subunits separate
– mRNA and the protein are released
What is RFLP?
RFLP = restriction fragment length
polymorphisms
Describe the process of RFLP.
*Restriction enzymes from bacteria cut DNA
molecules at specific sites.
– purpose may be for bacteria to degrade foreign
DNA.
– Restriction enzymes cut each strand of DNA at
recognition sequence
– palindromic sequence one strand is reverse of
sequence on the other
- Cutting DNA with restriction enzymes produces
fragments of DNA
– genetic differences and mutations, some recognition
sequences will be in different places in different
individuals
– some pieces longer than others
– different patterns - Electrophoresis
– DNA in electric current in gel
– DNA is negatively charged, moves to + pole
– Smaller pieces move faster. - Stain to see DNA
- Compare sizes with known standard or each other
- Gives a “DNA fingerprint”
Describe electrophoresis
- Electrophoresis
– DNA in electric current in gel
– DNA is negatively charged, moves to + pole
– Smaller pieces move faster. - Stain to see DNA
- Compare sizes with known standard or each other
- Gives a “DNA fingerprint”
What is PCR?
Polymerase Chain Reaction (PCR)
* For very small amounts of DNA
* DNA polymerase enzyme used to copy and increase
the amount of DNA
* Heat stable DNA polymerases important for PCR
– isolated from bacteria living in hot springs in Yellowstone
National Park
– Thermostable enzymes that are stable at higher temperatures
than those of most organisms.
Describe the PCR process.
- High temp 95ºC(around 200ºF)
– Weaken the hydrogen bonds
– Two strands of DNA separate - Temperature is lowered (50ºC)
– Strands replicated if DNA polymerase and the
nucleotides are present - After DNA replicated, heat again to separate new
strands and start replication again. - Thermostable DNA polymerase survives
repeated cycles of heating and cooling and is
still active - Repeated cycles of this process produces many
copies of what was originally a small amount
of DNA.
Describe the process of sequencing.
- Amplify fragment of interest by PCR
- Make complementary DNA fragments with terminator NTPs (when it gets incorporated into new chain stops elongation) that are fluorescently labeled.
- Separate fragments according to size by electrophoresis
Describe the part that DNA plays in forensics.
- VNTR (variable number of tandem repeats) DNA sequences
with runs of short, repeated sequences, such as GTGTGT - 4 to 40 repeats in different individuals.
- Individuals usually inherit a different variant of each VNTR
locus from their mother and from their father - two unrelated individuals therefore do not usually contain the
same pair of sequences. - Many VNTRs in human genome.
- For variability at 5-10 different VNTR loci, the odds that two
random individuals would share the same fingerprint by
chance are approximately one in 10 billion
Define a cell cycle
*Cell cycle: sequences of changes that a cell passes through between divisions
– Relatively long time duplicating structural components
* chloroplasts, mitochondria, membranes, DNA
– Relatively short time in cell division
* Cell division: division of components leading to
two daughter cells
Cell cycles and cell divisions carefully
regulated
– Want daughter cells identical to parent cell.
Define cell division
division of components leading to
two daughter cells
