Transcript DNA and Reproduction

Sexual Reproduction and
Meiosis
Sexual Reproduction Overview
• Requires the union of a sperm cell (male)
and an egg cell (female) from separate
parents.
• This union is called fertilization.
• Fertilization creates a zygote.
• A zygote has a full set of chromosomes. It
is diploid in number.
Sexual Reproduction Overview
• Diploid = 2n [ex. humans, n=23. 2(23)]
• Haploid means that a cell has half the
number of chromosomes in a cell.
• Haploid = n [ex. Human n = 23]
• Each chromosome has a match in the
nucleus that is very similar.
Meiosis Overview
• This creates pairs of matching
chromosomes for each cell.
• Meiosis is cell division in sex cells.
• Two divisions occur.
• Start with one sex cell, end up with four.
• A full set of chromosomes will be reduced
to half the number in each sex cell.
• Diploid cell to 4 haploid cells.
Sexual Reproduction Overview
One duplicated
chromosomes
Each chromosomes has a
match. These are
homologous chromosomes.
Each parent must only
contribute half of the
required chromosomes.
Homologous
chromosomes
Meiosis meets this
requirement creating
haploid cells.
Draw this Venn Diagram
Mitosis and Meiosis Compared
Mitosis
Meiosis
Mitosis and Meiosis Compared
Mitosis
•Diploid cell
•2 new cells
•1 division
•Anaphase –
sister chromatids
separate
Mitosis and Meiosis Compared
Meiosis
•Haploid cell
•4 new cells
•2 division
Only the pairs are
separating
•Anaphase I –
sister chromatids
stay together
Mitosis and Meiosis Compared
Meiosis
Mitosis
Common to both
•Nucleus breaks up
•Chromosomes line
up in the center
•Chromosomes
separate
•Cytokinesis occurs
Mitosis and Meiosis Compared
Meiosis
Mitosis
Common to both
•Diploid cell
•Nucleus breaks up
•Haploid cell
•2 new cells
•Chromosomes line
up in the center
•2 new cells
•1 division
•Anaphase – sister
chromatids separate
•Chromosomes
separate
•Cytokinesis occurs
•1 division
•Anaphase I – sister
chromatids stay
together
What is it?
• DNA is:
– A molecule
– Deoxyribonucleic acid
– Stores hereditary material
– A code of instructions
• For an organisms growth
• For normal functions
• For creating proteins
What is it?
• DNA is:
– Found in the chromosomes of a cell’s
nucleus
– Is copied and passed to new cells
– The key to biological life
Structure of DNA
• Each molecule consists of:
– A five carbon sugar (deoxyribose)
– A phosphate group
– A nitrogen containing base (4 total)
• Thymine
• Guanine
• Cytosine
• Adenine
Structure of DNA
• Each molecule is:
– A double helix (spiral structure)
• Think of a ladder that has been
twisted
Copying of DNA
• Before a cell divides the DNA found in
chromosomes must duplicate.
• Here’s how:
• Nitrogen bases separate (like unzipping
a zipper).
• This creates 2 halves of DNA that serve
as a pattern.
Copying of DNA
• An enzyme synthesizes the matching
halves of DNA.
• The 2 new DNA halves match up to the
original DNA.
• The cell is now ready to divide.
• Now look at the board and let’s
illustrate.
Functions of DNA
• Purposes of DNA
– Stores information for making you
like you are (eye color, hair color, etc)
– Provides the code for making
proteins
• Proteins build cells and tissues in
your body
• Proteins also act as enzymes that
trigger many chemical reactions in
your cells
Functions of DNA
• Making proteins
– Proteins:
• Are made of amino acids
• Instructions for each protein are
found on a GENE.
–A gene is a section of DNA on a
chromosome
»Look at figure 16 on page 112.
Functions of DNA
• Making proteins
• Genes provide the code and are in
the nucleus
• Proteins are made in ribosomes in
the cytoplasm
• The codes for making proteins are
carried from the nucleus to the
ribosomes by another nucleic acid
called RNA.
Functions of RNA
– Three types
1. messenger RNA (mRNA)
2. transfer RNA (tRNA)
3. ribosomal RNA (rRNA)
Look at page 113. We will discuss figure 17 to learn
about RNA and making proteins.