Unit 2 Flashcards
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
What is PLOIDY
number of sets of chromosomes in the nucleus of a cell.
Define a haploid
typically gametes such as egg or sperm
Define a diploid
Diploid-zygote
* Has two versions of each
chromosome, one from mom and
one from dad. These are called
homologous chromosomes
How many chromosomes do humans have?
46
What are plants that contain four or six chromosomes called?
tetraploid or hexaploid
Define homologous chromosome
Paired chromosomes. They essentially have the same gene sequence, loci (gene position), centromere location, and chromosomal length. Although they may have the same genetic sequence and loci, they may differ in alleles.
Define the interphase portion of the cell cycle
- interphase: long phase cell replicates
chromosomes and synthesizes other cell
constituents - Interphase: G1, S and G2
Define interphase: G1
G1 (Gap1) Phase
– Cell increases in size, synthesizes enzymes, ribosomes, membranes, microtubules and microfilaments
– Mitochondria and chloroplasts replicate
– Checkpoint at the end of this phase
* stops cycle if conditions are not favorable, or may signal beginning of next phase
Define Interphase: S phase
S Phase – replication of DNA and
histone proteins.
– Sister chromatids- replicated chromosomes
– 2 exact copies stay attached to each other at centromere
– Centromere: region where sister chromatids are attached.
– Appears as constriction
Define Interphase: G2
G2 Phase
– final phase of rapid protein synthesis, especially of microtubules and filaments
– at the end of this phase, DNA starts to condense to form chromosomes
– Checkpoint at the end of this phase, which may stop the cycle if conditions are not favorable or if mistakes in DNA replication
What happens in the process of mitosis?
Mitosis: Produces 2 cells with identical genetic content as parent cell (2n→2n or 1n→1n)
– Human: Most body cells
– Plants: most plant cells
Describe prophase in mitosis
DNA condenses: threadlike strands → chromosomes.
– Each chromosome was duplicated in S
– Two identical “daughter” chromosomes (called chromatids) joined together at the centromere
* Microtubules appear
– line up along the spindle axis with tubules converging at the poles away from the equator of the spindle
– The cancer drugs, vincristine and vinblastine, interfere with formation of the mitotic spindle.
* Nuclear membrane starts to break down
Describe metaphase in mitosis
Each chromatid develops kinetochore
– Kinetochore - protein complex attaches to microtubules extending toward one pole
– Kinetochore of the sister chromatid attaches to microtubules extending to the opposite pole
– Microtubules tug chromatids in opposite directions until line up along the equator of the cell
– Cohesin proteins hold chromatids together
– Taxol: anticancer drug, stabilizes the spindle preventing its breakdown and further steps in mitosis
Describe anaphase in mitosis
*Sister chromatids separate at the
centromere and move apart towards
opposite poles
– separase enzymes cut cohesins
* After separation, chromatids are called daughter chromosomes
Describe telophase in mitosis
*New nuclear envelope forms around the two new sets of chromosomes
* Spindle disappears
* DNA decondenses
Describe the process of cytokinesis
- Cell division resulting in two new
daughter cells each with a nucleus - In plants Phragmoplast: microtubules and microfilaments
– forms between 2 daughter nuclei - Secretory vesicles from the Golgi form a cell plate at the center of the cell
- Cell plate grows out toward the edges
- Cell membrane and new cell wall form
What happens in the process of meiosis?
Meiosis: Produces 4 cells with half the genetic content of parent cell (Reduction division), variation in which version of each chromosome (mom or dad) (2n→1n)
– Human gametes: Eggs, sperm
– Plant gametes: Eggs, sperm, pollen, spores
How is meiosis similar to mitosis? How is it different?
- Similar to mitosis
– DNA replication before mitosis (S phase) produces two chromatids joined by a centromere.
– Prophase: Chromosomes condense, nuclear envelope disappears, spindle forms
– Metaphase: Chromosomes line up along the mid-point of the spindle - Different from mitosis:
– Extra pairing step bringing together homologous chromosomes - Chromosome encoding different versions of same genes, one from mom and one from dad
- Need two divisions (Meiosis I and Meiosis II)
