Genetics  

What does have a plasma membrane and a cell wall composed mainly of cellulose and a polysaccharide?

Week Two Notes 9/7/16

Information from the Power Point = purple Verbal information = pink

Chapter Two Introduction 

Meiosis leads to production of gametes and mitosis leads to production of two cells each with  same number of chromosomes as parent cell.

The outcome of meiosis makes sperm/ eggs (gametes) and mitosis increases the number of  cells. Viruses cannot do mitosis or meiosis because they are not truly organisms.  

During nondivisional phases, chromosomes uncoil into a diffuse network within the nucleus:  chromatin. Living organisms have genetic material, composed of nucleic acid DNA. This does  not include viruses. In eukaryotes, transmission of genetic material involves mitosis and  meiosis.

What is the cell wall of bacteria?

If you want to learn more check out What are our closest living relatives?

2.1 Cell Structure and Genetic Function 

There are two types of cells: Prokaryotic cells and Eukaryotic cells.  

∙ Prokaryotic Cells- Has no membrane to confine the nucleus. Examples include Bacteria  and Archaea

∙ Eukaryotic Cells- Examples include animals, fungi and plants

All cells have: DNA, Plasma membranes and Ribosomes.

DNA spreads around as chromatin in the nucleus, and the nuclear membrane has holes for  things to get out (Example: RNA)

▪ Rough ER- This is where proteins are made. Without ribosomes this is the smooth ER. ▪ Smooth ER- This is where proteins are synthesized.

▪ Mitochondria- Powerhouse of the cell

The membrane defines the border of cells and protects cell from external environment.

What is a plant cell without a cell wall?

Plants: Have plasma membrane and a cell wall composed mainly of cellulose and a  polysaccharide.

Plants have an extra layer called a cell wall and without the cell wall the cells would not be able  to stand up.  We also discuss several other topics like How is mathematics shown in nature?

Bacteria have cells on their wall called peptidoglycan (-oglycan ending means proteins and  sugar).

Protoplast- A plant cell without a cell wall.

Animal cells membrane has glycocalyx with lots of carbs, sugars and glycoproteins. They also  have polysaccharides.

Function of the cell membrane is identification at cell surfaces.  

Nucleus

∙ Found in eukaryotes

∙ Membrane bound

∙ Houses genetic material, DNA

∙ DNA: complex array of acidic and basic proteins into thin fibers  

Bacteria divides and there is no membrane.

Nucleoid

∙ Found in prokaryotes Don't forget about the age old question of Where is stratified squamous epithelium found in the body?

∙ Not membrane bound

Cytoplasm Organelles:

Cytosol: Colloidal material surrounding organelles- fluid like consistency  

Cells can move on their own and the cytoskeleton is a flexible tubule structure that allows them  to contract and move. The cytoskeleton is made up of microtubules, and microtubules are made  of microfilaments. During cell division chromosomes move through the microtubules.  

Cytoskeleton made of extensive system of tubules and filaments  

▪ Microtubules: Made of tubulin

▪ Microfilaments: Derived from the protein actin

ER: An organelle: Compartmentalizes cytoplasm and it increases surface area for biochemical  synthesis.

SER: Smooth ER appears smooth in places- Site of fatty acid and phospholipid synthesis. RER: Rough ER is studded with ribosomes- Site of protein synthesis. If you want to learn more check out What type of muscle contraction occurs when the muscle contracts and shortens?

Process of Protein Secretion- Spread of ribosomes= Free ribosomes. When they are attached  to ER it looks rough because they are making proteins. After they have been made, they go to  the ER. Inside the ER other proteins called molecular chaperones supervise that the proteins have been made correctly before they can leave proteins then go to the golgi apparatus.

Mitochondria: Part of the cell in plants and animals that generate ATP

Chloroplasts: Found in plants, algae, and protozoans, and is responsible for photosynthesis.

Plants are self-sufficient because they use light and CO2 to make food. Food is made of sugar  and sugar is then used for energy.

“The heart of DNA is sugar. Without sugar there is no DNA. This is the same for RNA!” 

If there is no sugar then you cannot make membranes, and if you cannot make a membrane  you cannot have a cell. This is why sugars are very important.

Centrioles are found in centrosome of animal and plant cells and they organize spindle fibers for movement of chromosomes during meiosis and mitosis. Centrioles can hold microtubules  during mitosis and pull the chromosomes apart! If you want to learn more check out What were some of the characteristics of paleolithic society?

2.2 Chromosome Pairs in Diploid Organisms 

Humans have 22 pairs of chromosomes and are diploid organisms. In diploid organism  chromosomes occur in homologues pairs.  

Homologous chromosomes- Carry genes for the same inherited characteristics and may carry  different versions of the same gene.

Example: If mom has a CF gene and dad does not the offspring will have that gene from mom  (this does not necessarily mean the gene will be expressed). There can be hundreds if not  thousands of versions of the same gene. It is not simply normal or not normal. This is why  humans are so different.

Centromeres: Almost at the center of the chromosome

∙ Constricted regions on chromosomes – Where the chromosome is constricted matters  and the location of the constriction can change the function.

∙ Location of centromere establishes appearance of chromosome We also discuss several other topics like How does the criminal justice system respond to crime?

1. Metacentric-Middle

2. Submetacentric- Between middle and end

3. Acrocentric- Close to the end

4. Telocentric- At the end

The long arm is Q arm and the short arm is the P arm.

There are two kind of cells: Somatic cells and genomes.

∙ Somatic Cells: In the body other than reproductive organs

∙ Genomes: Genetic information in a haploid set

23 homologues pairs? True for females and false for males.

Exceptions include bacteria. Why? Because bacteria has a single chromosome and they  don’t have short arms or long arms because they are spread around and not condensed.  

Viruses-Most viruses have nuclear materials and there will be no proteins attached to it. Meiosis has one goal—to cut the number of chromosomes in half.

Gametes contain a haploid set of chromosomes.

Fusion of two gametes at fertilization results in a diploid zygote.

Female= 1 to 1. Male = 2 to 2.  

This shows the same meiosis can give different outcome numbers.

“ If you have 22 chromosomes, you do not have a sex!” 

∙ In egg= 22+ X (this is always constant) 

∙ In sperm= 22 +X (daughter) or 22+Y (son) 

Genome is the whole set of chromosomes. When the sperm and the egg fuse is called fertilization and the outcome of the fusion is gametes. Sex determining chromosomes are not  homologues, however they behave as if they are during meiosis.

“ As long as there is a Y chromosome it does not matter how many X chromosomes there are or  how big they are. It will be male!” 

2.3 Mitosis 

For mitosis you first double and then divide!

Mitosis partitions chromosomes into dividing cells.

Zygote: Single-celled fertilized eggs of multicellular organisms  

Karyokinesis: Genetic material partitioned to daughter cells during nuclear division  Cytokinesis: Cytoplasmic division follows

Cell Cycle: Composed of interphase and mitosis

Interphase includes:

– phase: DNA is synthesized

– Two gap phases (G1 and G2)

– G0: Point in G1 phase where cells are nondividing, but a metabolically active  state

Mitosis????G1????G0????Interphase????G2????Mitosis

Mitosis ????G1????G0. G0: is non dividing and is a point of rest ???? Interphase: Prepares for cell  division by dividing by duplicate cell materials in the S phase; does not happen in mitosis! The  purpose to divide= amount to degenerate ???? G2: makes sure there is enough for each daughter  cell ????Mitosis: Reduction of genetic material that has been created. Packs everything up.  Prophase: condenses, Metaphase lines everything up down the middle, Anaphase-ships the  material and Telophase- when the job is complete. Each phase has a check point. If something  goes wrong at a check point, mutations can occur.

De Novo- Genetic mutation not from parent, but from fertilized egg.

Prophase -Centrioles divide, move, and establish poles and the nuclear envelope breaks down.  The chromosomes condense and become visible. Sister chromatids: Two parts of each  chromosome, are connected at the centromere.

Prometaphase- The period of chromosome movement to equatorial plane of cell. The  equatorial plane referred to as metaphase plate. Centrioles reach poles and this is where  spindle fibers form.

Metaphase- Alignment of centromeres. The most condensed stage of chromosomes is located  during metaphase.

The nuclear membrane disappears at prophase and reappears when mitosis is complete at  telophase.

Telophase- Cytokinesis, uncoiling of the chromosomes and the re-formation of the nuclear  envelope. The spindle fibers disappear and the nuclear envelope reforms

Kinetochore:

o Proteins associated with centromere

o Spindle fibers bind to kinetochore; chromosomes migrate

Main Categories in Mitosis: Made up of different protein complexes:

▪ Cohesin -Protein complex that holds sister chromatids together

▪ Separase- Enzyme that degrades cohesin

▪ Shugoshin- Protein that protects cohesin from being degraded by separase

The check points at G1/S, G2/M and M assure that everything is correct and complete before  moving to the next phase.  

G1/S checkpoint

– Monitors size cell has achieved

– Evaluates condition of DNA

G2/M checkpoint

– Monitors if DNA replication is incomplete

– Monitors damaged DNA

M checkpoint

– Monitors successful formation of spindle fiber system and attachment to  kinetochores

“Any check point that goes wrong, will lead to cancer!” 

Cancer= Uncontrolled mitosis 

Anaphase: Disjunction- Sister chromatids separate and migrate to opposite poles.

2.4 Meiosis Reduces the Chromosomes 

Meiosis- Reduces genetic material by half

∙ Haploid gametes- Produces haploid gametes or spores, each containing one member of  a homologous pair of chromosomes

∙ Genetic exchange between members of homologous pairs of chromosomes  

“The first thing meiosis does is cut the chromosomes by half, the second thing it does is make  life interesting…”

…This is done by creating variation by changing the chromosomes. Without this step everyone  would be identical. Exchange of genetic material can be done anywhere, any number of times.  Genetic exchange occurs between the father and the mother. Example: Think of Legos. With  the same number and colors of Legos one person may build a house while another person may  build a dinosaur.

Meiosis I: Reductional division

Meiosis II: Equational division  

DNA synthesis Occurs during interphase, before the beginning of meiosis I and does not occur  again before meiosis II. Both mitosis I and II have prophase, metaphase, anaphase and  telophase stages.

Prophase 1: First meiotic division. The five substages include:

∙ Leptonema- Chromosomes appear as long, single threads, unassociated with each  other.

∙ Zygonema- Each pair of homologous chromosomes is known as bivalent. ∙ Pachynema- Each bivalent becomes shorter, thicker, and splits into two sister  chromatids called tetrads.

∙ Diplonema- Within tetrads, sister chromatids separate, Chiasma: Where chromatids are  still intertwined.

∙ Diakinesis- Nucleus and nuclear envelope break down and the centromeres attach to  spindle fibers.

Nondisjunction happens when something in the genetics goes wrong. It leads to a chromosome  exchange that is wrong. Example: Boy with 2X chromosomes and 1Y. It can happen to any of  the chromosomes.  

∙ Example- In humans when this occurs on chromosome 21, the offspring will have Down  Syndrome.

Nondisjunction may or may not occur and how often it occurs depends on the parents.