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35 Cards in this Set

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What is the Definition of a Genome?

The complete haploid genetic information of a cell or organism, DNA that contains that information


-Human genome = 3.2 billion bp

Eukaryotic Chromosomes

Chromosomes: DNA and proteins


DNA stretched out = 2 meters long


DNA must be packaged to fit inside nucleus of cell

What are the three elements of a chromosome?

Telomere: Caps on tails of DNA


Replication Origin: Can be multiple


Centromere: heterochromatic region where kinetochore assembles. Links sister chromatids in the middle of the X where they link



DNA packaging

46 chromosomes total


22 from father


22 from mother


2 sex chromosomes


Chromosomes are made from chromatin.

Homologs

2 copies, diploid, "homologous chromosomes"

Compacation

DNA wraps around histone for a "bead on a string" model.


Compacts DNA X3.


Histone located in center with two wraps of DNA arround it.


Negative charge DNA attracted to pos of histone

Nucleosome Structure

"Beads on a string" form of chromatin


Core histones of nucleosome (200 pb of DNA)


Nuclease digests linker DNA which releases nucleosome. (11 nm).


Dissociation into octameric histone core,


146-nucleotide-pair double helix.


Histone core dissociated into H2A, H2B, H3 and H4 (X2 of all)



The 30 nm fiber

Nucleosome units made into 30 nm fiber. Compaction X7


Structure hard to determine, DNA may be altered when extracted


Requires Histone 1 (H1). Attaches to DNA to link histone cores together (compaction)


- creates zig-zag model



Final stage of condensation

Occurs at mitosis


DNA is compacted 10,000 X original DNA strand


Ends as 1400 nm in length compared to original 2 nm of naked DNA





What is Heterochromatin?

Type of compaction:


- Highly compact and transcriptionally inactive


- localized regions in nondividing cells (centromeres and telomeres)

What is Euchromatin?

Type of compaction:


- Less condensed, capable of gene transcription


- Located in most regions of non-dividing cells




(Turn into heterochromatin once divided)

Histone Tail

Histones not perfectly circular due to tail


Modification usually on N-terminus.


Includes:


- Acetylation


- Phosphorylation


- Methylation


- Ubiquitination



Homologues

Species that is diploid, Members of a pair of chromosomes


One from Mother


One from Father


Contain same genes but different alleles



Mitotic Cell Division

- Cell divides to produce two new cells, genetically identical


-Mother: Daughter + Daughter



The Cell Cycle of Mitosis

1. Interphase ( G1, S, G2)


2. Mitosis:


- Prophase


- Prometaphase


- Metaphase


- Anaphase


- Telophase


- Cytokinesis





Mitosis

Sorting process, each daughter cells gets correct number/ type of chromosomes



Mitotic Spindle

Responsible for organizing and sorting the chromosomes

Centrosomes

Microtubule organizing center


-Come from mitotic spindle



What are the different microtubules?

-Astral


-Polar


-Kinetochore

Prophase and Prometaphase

Chromosomes condense


Nuclear envelope breaks down


Mitotic spindle forms


centrosomes move apart. go to two poles


Spindle fibers interact with sister chromatids


Kinetochores on sister attach to kinetochore on poles



Metaphase

Chromosomes are aligned along metaphase plate



Anaphase

Chromosomes segregate to opposite poles



Telophase

Chromosomes at opposite poles. Membrane forms

Cytokinesis

Cell divides (Different for plants/ animals)


- Animals: Cleavage furrows


- Plants: Cell wall forms in center of cell. Expands toward edges until it divides



Meiosis

Sexual reproduction. Requires fertilization event. Two haploid gamates unite to create diploid cell called zygote.


-Meiosis: Process by which haploid cells are produced from cell originally diploid



Mitosis vs Meiosis

Mitosis: Chromosomes singly line up at the metaphase plate.




Meosis: Pair before lining up at the metaphase plate

Zygote

Diploid cell: two haploid gamates unite

Bivalent



Homologous pairs of sister chromatids. lying side by side to form bivalent (tetrad).


Process called synapsis



Crossing Over

Physical exchange between homologous within a bivalent


Required for correct segregation of homologous in most species


Increases genetic variation


Chiasma: Cytologically observable site of crossover in bivalent



Haploid Dominant Species

Multicellular organism is haploid


Many fungi and protists



Diploid Dominant Species

Most animal species


Haploid gametes are a specialized type of cell

Name a few chromosomal mutations

Deletions: segments missing


Duplications: Section occurs 2 or more times in a row


Inversions: Self-explanatory


Translocations: One segment becomes attached to another chromosome



Aneuploidy

Alternation in number of particular chromosomes


Total number not an exact multiple of a set



Trisomic

Normal 2 copies of a chromosome plus a 3rd


2n + 1, Trisomy 21

Monosomic

Missing one of normal copies of a chromosome


2n - 1, XO