CHAPTER 12 REVIEW-1

prokaryotic vs eukaryotic: structure

• Prokaryotic DNA: Circular, single chromosome located in the nucleoid region, no membrane-bound nucleus.

• Eukaryotic DNA: Linear, multiple chromosomes located in the nucleus, organized with histone proteins into chromatin.

DNA replication before

• Chromosomes exist as single-stranded structures.

• DNA exists as one copy in the cell.

DNA replication after

• Each chromosome is duplicated, and two identical chromatids (sister chromatids) are formed.

• These sister chromatids are connected by a centromere and will eventually separate during cell division.

Chromosomes

• A chromosome is a tightly coiled structure of DNA and proteins (chromatin).

• Each chromosome consists of one molecule of DNA.

• Found in both prokaryotes and eukaryotes, though eukaryotes have multiple chromosomes.

• found during cell division

Chromatids

• Chromatids are the two identical halves of a chromosome after DNA replication.

• Chromatids are joined together by a centromere.

• They separate during cell division (mitosis or meiosis).

• present after DNA replication during the S phase & during stages of mitosis & meiosis before separation

Centromeres: purpose

• The centromere holds the two sister chromatids together after DNA replication.

• It is crucial for proper chromosome segregation during cell division.

Centromeres: Function

Ensures that each daughter cell receives the correct number of chromosomes by anchoring the chromatids to the spindle apparatus.

Centromeres: structure

• The centromere is a constricted region of the chromosome.

• It contains specialized DNA sequences and proteins that aid in the attachment of spindle fibers during cell division.

Kinetochores: Structure

• The kinetochore is a protein complex that forms at the centromere of a chromosome.

• It connects the centromere to the microtubules of the spindle apparatus.

Kinetochores: function

the kinetochore is responsible for attaching the chromosome to the spindle fibers and facilitating the movement of chromosomes during mitosis and meiosis.

Haploid

one complete set of chromosomes n=23

Diploid

two complete sets of chromosomes 2n=46

Mitosis

prophase-DNA replicates, Metaphase-chromosomes line up in the middle and attach to centromere, Anaphase-chromosomes start to separate, Telophase-stuff in cell starts to rebuild then pull apart from each other

meiosis

• Meiosis I: Reduces chromosome number by half (from 2n to n).

  • Prophase I: Chromosomes condense, homologous chromosomes pair.

  • Metaphase I: Homologous pairs align.

  • Anaphase I: Homologous chromosomes separate.

  • Telophase I: Two haploid cells are formed (n chromosomes).

• Meiosis II: Similar to mitosis, where sister chromatids separate (no chromosome replication beforehand).

G0

cells are not dividing

G1

cells grows and preforms normal functions chromosomes are replicated

S

Synthesis DNA replication

G2

Growth phase 2 cell continues to grow and prepares for mitosis