Biology - Unit 1 - Gentics

Modern Cell Theory:

-all living things are composed of cells
-cells are the basic unit of all organisms
-all cells arise from preexisting cells

Eukarotic cells

Has a membrane-bound nucleus and membrane-bound organelles , Can be Multi or unicellular

Prokarotic cells

-No nucleus
-No internal membrane
-No major organelles
-Unicellular

A,C, G, T meaning

adenine (A), cytosine (C), guanine (G), and thymine (T)

Genes

Sequences of DNA that code for a particular protein resulting in specific traits or functions.

Pyrimidine

Cytosine & thymine - structure made up of 1 ring

Purines

Bases with a double-ring structure.
Adenine and Guanine

Chromatin

Clusters of DNA and proteins in the nucleus of a cell

complementary base pairing

In DNA, T pairs with A; G pairs with C;

Haploid

A cell that contains a single set of chromosomes


Haploid can also mean the number of chromosomes in egg or sperm cells.
In humans: Gametes (Sex Cells), 23 chromosomes

Diploid

A cell that contains 2 sets of chromosomes(of both egg and sperm)

(46 in humans)

Longest part of cell cycle (and longest stage of that part)

Interphase (Growth 1)

What happens in growth 1 interphase .

- Regular funtions
- Protein is produced
- Organelles are produced
- Cytoplasm volume increases

What happens in Synthesis (Interphase)

- DNA inside the Nucleus is replicated.
- Now DNA exists as uncondensed fibres called chromatin

What happens in Growth 2 (Interphase)

- Organelles are duplicated
- Centrioles replicate
(2nd and shortest growth stage)
- Cells prepare for cell division

Prophase

- Chromatin condenses into chromosomes
- Supercoiling Occurs
- Involved histone protein and enzymes
- Replicated chromosomes are called sister chromatids
- These are connected in the middle by a centromere
- Spindle Fibres form from centrosomes
- Together the spindle fibre and the centrome from the spindle apparatus. This moves and organises the chromosomes during mitosis.
- centrosomes move to opposite poles
- Nucleus disappears and nuclear membrane disintegrates


Supercoiling - repeated coiling the DNA molecule to make the chromosome shorter and wider

Metaphase

- Spindle fibres attach to the centromere and guide the sister chromatids to the equator

Anaphase

- Centromeres split to separate sister chromatids (now called chromosomes)
- Spindle fibres shorten, pulling chromosomes to opposite poles

Telophase

This begins when chromosomes reach the opposite poles

- Chromosomes start to unwind into strands of less vissble chromatin
- Spindle fibres break down
- Nuclear Membrane forms around new NUCLEI
- Nucleolus forms within each new nucleus

Cytokinesis in animal cells

Cell membrane pinches inward making a cleavage furrow.
- Furrow keeps deepening until 2 new cells are formed.
- Each with its own new nucleus
- Two Daughter cells are formed

Cytokinesis in plant cells

Vesicles containing cellulose are produced in the golgi body and line up along the equator.
- They burst simultaneously to form a new cell wall (Called a cell plate)
- A new cell membrane forms shortly after

DNA full form.

deoxyribonucleic acid

DNA structure

Double Helix (Similar to a long ladder)

Nucleotides have 3 parts

- Deoxyribose sugar
- phosphate group
- Nitrogenous base

Why do cells divide?

- Growth and development of multicellular organelles
- Tissue Repair
- Asexual Reproduction
- Embryonic development

Nucleosome

Mixture of protein and DNA

Somatic Cells

Body cells

- Liver, nerve, skin

- 46 chromosomes (full set for humans) - diploid #

Gametes

Sex Cells

- Sperm, Egg

- 23 Chromosomes (half set for humans) - Haploid #

Cell memebrane

Fluid- mosaic structure

Separates the cell interior from the outside world and controls the movement of materials in and out of the cell.

Present in both animal and plant cells.

Cell Wall

Surrounding the cell membrane.

Protects and supports the cell allowing to pass materials to and from the cell membrane by passing through pores.

Present in only plant cells

Nucleus

The command center of cell

Contains blueprints for creating protein, determining the structure for the cell and its functions.

Contains:

DNA
Chromatin --> Chromosomes
Nuclear envelope (Nuclear membrane)
Nucleolus

found in both plant and animal cells

Nucleolus

A specialized area of chromatin inside the nucleus responsible for producing ribosomes (Containing RNA, proteins, and chromatin)

found in both plant and animal cells

Cytoplasm

Surrounds Organelles

two different parts

Cytosol : liquid protion

Organelles

found in both plant and animal cells

Vacuoles

- Membrane-bound sacs for storage, digestion, and waste removal

found in both plant and animal cells (smaller but multiple for animal cells while plant cells usually have one large vacuole)

Vesicles

small membrane sacs that specialize in moving products into, out of, and within a cell

found in both plant and animal cells

Ribosomes

Tiny two part RNA-proteins complexes

- Found in the cytoplasm and attached to Rough ER

Function: Synthesis of proteins

found in both plant and animal cells

General Information about Meiosis

- 2 Divisions (Meiosis 1 and 2)
- Occurs in cells in reproductive tissues (Testes and Ovaries)
- Produces Unique Gametes (sperm or egg) with haploid # (One set) of chromosomes (23/46 chromosomes for humans)
- Gametes combine (fertilization) to produce a diploid zygote

diploid zygote

the product from the combination of two haploid gametes during fertilization (meiosis)

Meiosis 1

- Homologous chromosomes separate
- # of chromosomes is halved

Prophase 1 (meiosis)

- Homologous chromosomes pair up (Synapsis)
- Form tetrads made of 4 chromatids
- Crossing over occurs
- Centrioles move to opposite poles

Metaphase 1 (Meiosis)

- Tetrads line up at the equator
- Independent assortment occurs
- Spindle fibres start to shorten (not visible)

Anaphase 1 (Meiosis)

- Spindle fibres shorten further.
- Homologous chromosomes separate (Sister chromatids stay together)

telophase 1 and cytokinesis (meiosis)

- Nuclear membrane begins to reform
- Cleavage furrow begins

Cytokinesis:
- Two haploid daughter cells result

Meiosis 2

- Sister chromatids separate
- Chromosome number stays the same

- No DNA replication before prophase 2***

Prophase 2 (meiosis)

Very brief

- Spindle fibres form
- Nuclear membrane is close to disappearing
- Centrioles start to move to opposite poles

Metaphase 2 (meiosis)

- Sister chromatids line up at the equator
- spindle fibres shorten (not visible)

Anaphase 2 (meiosis)

- Sister chromatids separate
- Spindle fibres shorten further

telophase 2 and cytokinesis

- Nuclear membrane re-forms
- Cleavage furrow forms

- Following cytokinesis 4 unique haploid daughter cells are formed

Crossing over

- AKA Genetic recombination
- Homologous chromosomes exchange portions of DNA
- points where chromatids break and re-unite are called chiasmata

independent assortment

- AKA Random Assortment
- Random alignment of chromosomes at the equator, which move to opposite poles

- results in gametes with a random mixture of maternal and paternal chromosomes

Pre- Interphase (meiosis)

- Goes through regular functions
- Supercoiling may begin

Post interphase (meiosis)

- DNA duplicates
- cell increases in size
- cell gets ready for meiosis

Tetrads

homologous chromosome pairs

Endoplasmic Reticulum (ER) (rough)

Membrane-bound tubes - involved in transportation.
- Ribosomes attached
- involved in protein synthesis

A n P

Smooth ER

Membrane-bound tubes involved in transportation

no ribosomes,
synthesizes lipids

A n P

Golgi complex (Golgi apparatus)

Stack of curved membrane sacs

- Packages, processes, sorts, and distributes proteins, lipids, and other substances with IN the cell

A n P

Lysosomes

Produced by Golgi complex/ Golgi apparatus

- Membrane-bound sacs
- make compartments in cells that digest food, destroy invading bacteria, and break down damaged organelles

A

Mitochondria

Double Membrane Structure

- involved in cellular respiration
- contains their own DNA

A n P

Chloroplasts

Double membrane structure

- contains chlorophyll, which absorbs light energy during photosynthesis

P

Cytoskeleton

Network of protein fibres throughout the cytoplasm

- provides structure, shape, support, and assists in cell mobility

A n P

Cilia

Many shorter appendages

- can enable movement of sweep out debris in lungs

A

Flagella

One or Two long appendages

- Similar to a tail, it propels the cell.

A

Phenotype

The appearance of an organism, observable characteristics

Genotype

Describing the set of alleles an organism has for a gene (ie BB or Tt)

Hetrozygotes

Describing a genotype that contains two DIFFERENT alleles for a trait (ie Bb) (Carrier or Hybrid)

Homozgyous
- Dominant
- Recessive

Describing a genotype that contains two of the SAME alleles for a trait (ie bb or BB) (PURE BRED)

- BB
- bb

Punnett Squares

A mathematical model used to predicts possible gene combinations.

Monohybrid Crosses

Mating of two individual for ONE particular trait

Allele(s)

Variation of genetic sequence at a particular region on a chromosome.

Trait

specific characteristic of an individual (Eye color : brown, blue, red)

What did Gregor Mendel do?

- Made first scientific attempt to explain inheritance
- Performed experiments to find out how pea plants inherit traits
- He identifies and used seven pairs of contrasting traits in pea plants

Gregor Mendel's step 1?

Step 1)

The parent generation: pure yellow pods X pure green pods

- Pure bred or true breading plants, when self fertilized produce offspring identical in appearance to itself.

Gregor Mendel's step 2?

Step 2)

Cross purebred (F1)

P = Yellow X Green
F1 result= All green pods (meaning Green is dominant)

Gregor Mendel's step 3?

Step 3)

F1 X F1 (Self pollinating to make (F2))

P = Green X Yellow
F1 = All Green

F2 = 1 Yellow and 3 Green (Yellow reappeared)

Therefore Yellow pods are recessive.

Gregor Mendel's Conclusions

- There is a gene for pod color
- Organisms inherit different forms of a gene
- Called Alleles - From each parent

- Alleles can we dominant or recessive.

Genetic disorders can result from:

- Single gene Defects
- Chromosomal Defects

Mistakes in Meiosis (2 General outcomes that can occur as a mistake in meiosis)

1. Abnormal Chromosome Number
2. Abnormal Chromosome Structure

Aneuploidy

A cell with too few or too many chromosomes

- Caused by a nondisjunction in meiosis

Nondisjunction

- The abnormal separation of chromosomes
- Can occur in Anaphase during meiosis 1 and 2

Nondisjunction in Meiosis 1

- All resulting gametes will have an abnormal chromosome number

Nondisjunction in Meiosis 2

- Half of the resulting gametes will have an abnormal chromosome number

Monosomy

- One less chromosome in a pair (ie 45 in each cell)

Polysomy

- One more chromosome in a pair (ie 47 in each cell)

Polyploidy

- posses more than two sets of chromosomes
- Zygote produced is triploid (3n)
- A more severe result of nondisjunction

What happens after nondisjunction?

- In most cases it results in a non-viable zygote which is spontaneously aborted, often before the pregnancy can be detected
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- If the child survives, they will show effects associated with the missing or extra genetic information carried on the chromosome involved in the aneuploidy

Down Syndrome

(Trisomy 21)

- 3 Copies of chromosome (21)
- 47 Chromosomes total

- Mild to moderate mental impairments
- Think tongue, speech, and facial defects

Turner Syndrome

- Female with only one X chromosome (XO)
- 45 chromosomes (monosomy)

- Sterile Females (cannot reproduce)
- Secondary sexual features do not develop fully

Klinefelter Syndrome

- Male with XXY
- 47 Chromosomes (Trisomy)

- Affects male sexual development - DO NOT Produce enough testosterone
- Breast enlargement, decreased facial and body hair infertility

Supermale or Super female

Supermale(XYY) or Super female(XXX)

- Trisomies (47 chromosomes)

- No symptoms
- Phenotypically the same as 'normal' males and females

Cri Du Chat Syndrome

- Partial deletion of chromosomes

- Improperly constructed laryns produces a 'cry of the cat' sound to voice
- Mentally challenged

Fragile-X Syndrome

- 700 repeats of part of X chromosome

- Abnormal Facial Features
- Mentally challenged

Abnormal Chromosome Structure

- Can occur during crossing over in meiosis 1
- pieces of genetic information do not reattach properly to chromosomes

4 types of changes that can occur (Abnormal Chromosome Structure)

Deletion, Duplication, Inversion, Translocation

Deletion

- Portion of a chromosome is lost (may contain genes)
- May be caused by virus, radiation, or chemicals

Duplication

- A part of a chromosome is repeated (Repeated region could include a gene)

Inversion

- Reverses a fragment of the original chromosome
- May cause problems with synapsis during meiosis
- May lead to difficulties with reporduction

Translocation

- A fragment of one chromosome attaches to a non-homologous chromosome

Mutations

- Any change in a gene that is accompanied by a loss or change in the functioning of the genetic information
- Can occur spontaneously

Mutagen

Any factor that can cause mutations

Mutations can occur in...

- Somatic cells: Usually go unnoticed unless a significant number of cells are involved

- Gametes: The mutations can be passed on to produce an entire organism with this mutation in every cell can can continue on for many generations