BIO 011 Lecture Notes - Lecture 14: Asexual Reproduction, Dna Replication, Prokaryote
Chapter 11: The Cell Cycle, Chromosomes, Genes and Mitosis
Four events must occur for cell division
- Reproductive signal: to initiate cell division
- Replication of DNA
- Segregation: distribution of the DNA into the two new cells
- Cytokinesis: separation of the two new cells
Prokaryotic cell division
- Cell division = reproduction (mostly)
- Only one circular chromosomes (mostly) (this one chromosome
divides)
o Covalently closed circle
o [In comparison, eukaryotes have many linear
chromosomes]
- No mitosis
- One origin of replication (ori) → origin starts at one point and
goes all the way around to the (ter) terminus.
o Ori – the origin where DNA replication begins, and it
ends at the terminus – the end
- Cytokinesis follows DNA replication immediately
- After one round of replication you get new poles in both cells that are identical to the poled in the
mother cell. Then they move to opposite sides of the cell. Cytokinesis by bacterial cytoskeletal
proteins in the middle of the cell → they contract, shrink in the middle, and seal off both
membranes to make 2 new daughter cells.
- This happens in about 20 minutes, complete separation of the cells into 2.
Eukaryotes
- Eukaryotes originate from single cell, fertilized egg.
- This cell results in gamete union and contains genetic material from both parents.
o [In comparison, prokaryotes have no genetic differences (if no genetic mutations) from
their parent]
o Eukaryotes are half genetically mom and half genetically dad
- Multi-cellular eukaryotes have development: cell reproduction by mitosis and specialization
o Taking the DNA blueprint and expressing it in different ways
- Sexual reproduction involves meiosis: leads to gamete formation
Eukaryotic Mitotic Cell Division:
- Unicellular
o Asexual reproduction
- Multicellular
o Growth
o Tissue replacement
o Asexual reproduction
- Makes genetically identical cells
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DNA Terms
- DNA
o Deoxyribonucleic acid
- Nucleotide sequence
o Unwind DNA and start from 3
prime end of one side because it
goes from 5 prime to 3 prime
- Chromatin = DNA + protein
- What is a chromatid?
o Each of the two threadlike
strands into which a
chromosome divides
longitudinally during cell
division. Each contains a double
helix of DNA.
- Histones have lysine on them
o DNA has a negative charge and
lysine has a positive charge
- Is 60 nm wide
- A chromosome is a set of genes
o After it is replicated, you have the same thing times 2. The name of the two strands
changes to chromatid and they are held together by centromeres.
▪ Chromosome = chromatid + chromatid
Prokaryotic Chromosomes
- haploid (1-n)
- Only one copy of each gene
- Cell division = reproduction
centromere
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Eukaryotic Chromosomes
- In eukaryotes, there are multiple chromosomes.
- Each cell (except gametes) has two copies of each
chromosome and therefore two copies of each gene.
- Idetial chromosomes are called homologous
chromosomes.
- Human have 23 pairs of homologous chromosomes.
- Diploid (2-n)
Chromosomes and Genes Concepts
- Gene
- DNA
- Nucleotide sequence
- Protein
- Chromatid
- Chromatin
- Allele
o Alternate forms of the same gene
o Difference in nucleotide sequence
o May or may not result in different protein
Chromosomes and genes in diploid cells
- Diploid cells have pairs of homologous chromosomes; one set from each parent.
- Diploid cells have two copies of each gene, one copy on each chromosome.
- Therefore, one copy of each gene is inherited from each parent.
- There may be differences in the DNA sequence for the copies of the same gene on homologous
chromosomes. These alternate forms of genes are called alleles.
- Different traits for the same character (Mendelian genetics) are the result of the expression of
different alleles of the same gene.
Gregor Medel’s Eperiets
- Studied heritable characters where there were clear distinctions between alternate traits
o Had any idea that traits were passed down ut did’t ko ho
- Character = an observable feature such as flower color
- Trait = a particular form of the character, such as purple or white flowers (allele)
- Heritable character = one that is passed form parent to offspring (gene)
- These characteristics were not blended together.
o Ex: plants: round and wrinkled make no intermediates. You either get round or wrinkled
or both. Not one that is slightly less wrinkled, or round
o Different alleles give different traits
- Different traits for the same character in Mendelian genetics are the result of the expression of
different alleles of the same gene.
- You inherit chromosomes from your parents!
- Cannot understand genetics if you do not understand what happens to chromosomes during
mitosis and meiosis
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Document Summary
Chapter 11: the cell cycle, chromosomes, genes and mitosis. Cytokinesis: separation of the two new cells. Segregation: distribution of the dna into the two new cells. Only one circular chromosomes (mostly) (this one chromosome divides: covalently closed circle. After one round of replication you get new poles in both cells that are identical to the poled in the mother cell. Then they move to opposite sides of the cell. Cytokinesis by bacterial cytoskeletal proteins in the middle of the cell they contract, shrink in the middle, and seal off both membranes to make 2 new daughter cells. This happens in about 20 minutes, complete separation of the cells into 2. This cell results in gamete union and contains genetic material from both parents. [in comparison, prokaryotes have no genetic differences (if no genetic mutations) from their parent: eukaryotes are half genetically mom and half genetically dad.
