case 2 Flashcards
Does crossing-over happen in mitosis or meiosis and what about independent assortment?
In meiosis crossing-over and independent assortment happens. In mitosis crossing-over and independent assortment does not happen.
Production/function of mitosis and meiosis?
Production of mitosis is asexual and from meiosis is sexual and the function of mitosis is growth. Embryo development, tissue repair. The function of meiosis is gamete formation.
(in meiosis) What happens in the interphase?
Three phases; G1 (first gap) The S phase and the G2 (secund gap). During al the phases of interphase, actually a cell grows by producing proteins and cytoplasmic organelles such as mitochondria and endoplasmic reticulum. During the s phase only Duplication of the chromosomes occurs, crucial for eventual division of the cell. in G2 it also completes preparations for cell division.
(in meiosis) What happens in the first prophase?
This is where the chromosomes are going to condense and thicken. They are going to line up with their homologous pairs. Crossing over appears here. Mitotic spindles start to form. Nuclear envelope breakdown occurs.
(in meisosis) what happens in the first metaphase?
(tip m= for middle the chromosomes are now going to be in the middle of the cell (on the metaphase plate)) the chromosomes are going to be in pairs in the middle. Each pair is lined up independently of other pairs( this is called independent assortment) both chromatids of one homolog are attached to kinetochore microtubules from one pole; the chromatid of the other homolog are attached to microtubules from the opposite pole.
(in meisosis) What happens in the first Anaphase?
(tip a= away)homologous pairs separate. Chiasma breaks down. the chromosomes are going to be pulled away. (note sister chromatids remain attached – both move to the same pole).
(in meisosis) what happens in the fist Telophase 1 and cytokinesis?
When telophase begins, each half of the cell has a complete haploid set of duplicated chromosomes. Each chromosome is composed of two sister chromatids; one or both chromatids include regions of nonsister chromatid DNA. Cytokines happens. Forming two haploid daughter cells.
(in meisosis) What happens in the secund prophase?
Spindles start to form. Chromosomes each still composed of two chromatids associated at the centromere, are moved by microtubules towards the metaphase 2 plate.
(in meisosis) What happens in the secund metaphase?
(tip m= for middle the chromosomes are now going to be in the middle of the cell (on the metaphase plate)) (because of crossing over in meisosis 1 (crossing over does not happen in meisosis 2) the two sister chromatids of each chromosome are not genetically identical. The kinetochore of sister chromatids are attached to microtubules extending from opposite poles.
(in meisosis) What happens in the secund anaphase?
(tip a= away) breakdown of proteins holding the sister chromatids together at the centrosome allows the chromatids to separate and move away toward the opposite poles: each chromatid has now become an individual chromosome.
(in meisosis) What happens in the secund telophase 2 and cytokinesis?
Nuclei from, the chromosomes begin decondensing and cytokinesis occurs. The meitotic division of one parent cell produces four daughter cells, each with a haploid set of (unduplicated) chromosomes
What does helicases do?
Are enzymes that Untwist the double helix at the replication forks, separating the parental strands and making them available as template strands.
What does single-strand binding proteins do?
Single-strand binding proteins bind to the unpaired DNA strands, keeping them from re-pairing. The untwisting of the double helix causes tighter twisting and stain ahead of the replication fork.
Explain primer and primase.
The RNA chain is called a primer and is synthesized by the enzyme primase. Primase starts a complementary RNA chain with a single RNA nucleotide and adds RNA nucleotides one at a time, using the parental DNA strand as a template. (the complete primer, generally five to ten nucleotide long, is thus base-paired to the template strand. The new DNA strand will start from the 3’ end of the RNA primer). (RNA nucleotides are later removed of the primer and replaced with DNA nucleotides)
What does topoisomerase do?
Is an enzyme that helps relieve this strain by breaking swivelling and rejoining DNA strands.
Explain DNA polymerase.
Enzymes that catalyse the synthesis of new DNA by adding nucleotides to the 3’end of the preexisting chain. Never the to the 5’end. Thus the new DNA strand can elongate only in the 5’ 3’direction. Requires a primer and DNA template strand, along with complementary DNA nucleotides. Polymerase adds a DNA nucleotide to the RNA primer and then continues adding DNA nucleotides, which are complementary to the parental DNA template strand to the growing end of the new DNA strand. (elongating)** Later door**
What are okaziki fragments?
The laggin strand is synthesized discontinuously, as a series of segments. These segments of the laggin strand are called Okazaki fragments (only in DNA).
Explain RNA polymerase.
Is an enzyme that Pries two strand of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, thus elongating the RNA polynucleotides. RNA
Explain the stages of transcription.
Figure 17.8 further explain. bacterie
* Initiation;
- After RNA polymerase binds to the promoter the polymerase unwinds the DNA strand and initiates RNA synthesis at the start point on the template strand.
- Elongation;
- The polymerase moves downstream unwinding the DNA and elongating the RNA transcript 5’ 3’after transcription has occurred, the DNA strand re-form a double helix.
- Termination;
- Eventually, the RNA transcript is released, and the polymerase detaches from the DNA
What is the lagging strand?
The other new strand of DNA elongating in mandatory 5’ 3’direction. (The DNA polymerase must work along the other template strand in the direction away from the replication.
What is replication fork?
Region where the parental strands of DNA are being unwound.
What is the promoter?
The DNA sequence where RNA polymerase attaches and initiates transcription. A crucial DNA promoter is the TATA box forming the initiation complex at a eukaryotic promoter)
Explain transcription factors.
A collection of proteins that help guide the binding of RNA polymerase and the initiation of transcription. Only after transcription factors are attached to the promoter does RNA polymerase bind to it (the whole complex of transcription factors and RNA polymerase bound to the promoter is called transcription initiation complex)
Explain RNA processing.
Both ends of the primary transcript are altered. Think about the 5’cap of the poly-A-tail. They share functions.
- They facilitate the export of mature mRNA from the nucleolus.
- They help protect the mRNA from degradation by hydrolytic enzymes
- They help ribosomes attach to the 5’end of the mRNA one it reaches the cytoplasm.
