biology semester two checklist

Positive and Negative Feedback Loops

·       Firstly, Homeostasis is the regulation and maintenance of the internal environment of the body.  

·       Homeostasis controls internal conditions with feedback loops

Positive Feedback Loops: the product amplifies the process that creates them (moves in the same direction).

·       less common homeostatic mechanism  

·       example is childbirth.

Negative Feedback Loops: the product inhibits the process that creates them (moves in the opposite direction) 

·       common homeostatic mechanism.

·       example is thermostat (controls body temperature) 

Endocrine System:
The endocrine system is composed of several glands that produce hormones essential for regulating various body functions. These glands include:

1. Hypothalamus: Links the nervous system to the endocrine system, controlling the pituitary gland.

2. Pituitary Gland: Known as the "master gland," it regulates other endocrine glands.

3. Pineal Gland: Produces melatonin, influencing sleep-wake cycles.

4. Thyroid: Regulates metabolism through thyroid hormones.

5. Parathyroid: Manages calcium levels in the blood.

6. Adrenal Glands: Produce hormones like adrenaline and cortisol, managing stress responses.

7. Pancreas: Regulates blood sugar via insulin and glucagon.

8. Gonads (Ovaries/Testes): Produce sex hormones, supporting reproduction.

9. Thymus: Important for immune system development in children.

Pathogens and Infectious Disease

·       Infectious Disease: involve invasion by a pathogen and can be transmitted from one host 
to another. E.g. Influenza, HIV, tuberculosis, malaria, and mad cow disease.  

·       Pathogen is an infectious agent that can cause illness or disease in its host.  E.g. prions, viruses, bacteria, fungi, protists and parasites.

Outcome of miosis vs meiosis: haploid/diploid clones/genetically same.

-          Chromosomes: DNA and the histones (proteins that help’s the DNA structure) associated with the DNA.

-          Diploid: found in all non-sex cells or autosomes of an organism body (with few exceptions). (two sets of chromosomes (2n)).

-          Haploid: (contains one set of chromosomes (n) and is a gamete/sex-cell).

-          Gene: the basic unit of heredity passed from parent to child.

Mitosis (makes body cells): the process by which a cell replicates its chromosomes and then segregates them, producing 2 identical nuclei in preparation for cell division.

-          You begin with diploid (2n) – two sets of chromosomes (23 from mum and 23 from dad) in total for humans that is 46.

-          During interphase the cell duplicates the chromosomes (even when duplicated still say 46 chromosomes even though there is now 92)

-          Next the chromosomes go through the phases of PMAT: prophase, metaphase, anaphase, telophase.

-          Results in two identical diploid cells. (46 chromosomes in humans)

Meiosis (makes gametes e.g. sex cells):

-          You begin with diploid (2n) – two sets of chromosomes (23 from mum and 23 from dad) in total for humans that is 46.

-          During interphase the cell duplicates the chromosomes (even when duplicated still say 46 chromosomes even though there is now 92)

-          Next the chromosomes go through the phases of PMAT twice: prophase, metaphase, anaphase, telophase.

-          Results in four non-identical cells (gametes) – male create sperm cells and women create egg cells. These gametes are haploids, meaning they have half the number of chromosomes than the original (23 chromosomes in humans)

DNA structure including subunits and bases:

·       DNA is made of four chemicals that form pairs in different combination – Adenine, Cytosine, Guanine, Thymine (A,T,G,C).

1.       Nucleotide Subunits
each subunit consists of:

·       Phosphate group: Provides structural backbone.

·       Deoxyribose sugar: A five-carbon sugar unique to DNA.

·       Nitrogenous base: Determines genetic coding.

2.       Nitrogenous Bases
the bases are categorised by:
- purines (larger two ringed molecules): Adenine, Guanine.
- pyrimidines (smaller, single-ringed molecules): Cytosine, Thymine

3.       Base Pairing
- Adenine pairs with Thymine
- Guanine pairs with Cytosine

4.       Double Helix Formation

·       DNA strands are antiparallel, running in opposite directions (5’ to 3’ and 3’ to 5’).

·       Base pairing between complementary strands stabilizes the helix.

Complimentary Base Pairing

There are chemical cross-links between the two strands in DNA, formed by pairs of bases held together by hydrogen bonds. They always pair up in a particular way, called complementary base pairing:

• thymine pairs with adenine (T-A)

• guanine pairs with cytosine (G-C)

Difference between DNA and RNA

Protein Synthesis

 Protein synthesis is the process through which cells produce proteins, and it occurs in two main stages: transcription and translation.

1. Transcription:

• Takes place in the nucleus.

• DNA is unzipped by the enzyme helicase, exposing a single strand of the gene.

• RNA polymerase moves along the DNA strand, joining free RNA nucleotides to form a complementary mRNA strand.

• Once the mRNA strand is complete, RNA polymerase detaches, and the DNA strand rejoins.

2. Translation:

• Occurs in the cytoplasm.

• The mRNA strand attaches to a ribosome, which reads the mRNA sequence in sets of three bases called codons.

• tRNA molecules transport specific amino acids to the ribosome, matching their anticodons to the mRNA codons.

• Amino acids are linked together in a chain based on the codon sequence, forming a polypeptide, which eventually folds into a functional protein.

Key Steps to Determine Amino Acids:

1. Observe the given DNA sequence.

2. Transcribe it into the mRNA sequence.

3. Divide the mRNA sequence into codons.

4. Use a codon chart to identify the amino acids encoded by each codon.

Pedigree Charts

Symbols of the pedigree charts:
- square indicates a male.
- circle indicates a female.
- horizontal line indicates marriage/sex.
- p-generation is the parent (first generation) then continues with F2, F3, etc.
- a coloured shape represents a person who is affected.
- an empty coloured shape represents a person who isn’t affected.
- a carrier is a person who has one allele for a recessive trait. they are not affected but can pass the gene on. they are represented by either half colouring or a dot.​ carriers are always heterozygous for the trait.​

Types of Mutations

·       mutations: is any permeant change in the DNA sequence of a gene/s

·       if the change is single gene, it’s called a genetic mutation, if it affects most of the chromosomes, it’s called chromosomal mutation.

·       Mutations can be beneficial, neutral but mainly harmful.

·       Mutation rates are increased by mutagens (uv-radiation, cigarettes, human papillomavirus).

Effects: (mutations can affect organisms in three ways)

·       Beneficial: the organism a better chance to survive.

·       Neutral: doesn’t change the amino acid.

·       Harmful: proteins that don’t function normally, cause genetic disorder.

Types of Genetic Mutation

·       Substitution Mutation: exchange base for another. E.g. sickle cell anaemia.

·       Frameshift Mutation: (addition and deletion) can occur via random or mutation. – affects the ‘reading frame’ of the DNA strand. It results in the production of non-function proteins.

Mutation involving Chromosomes number ‘non-disjunction’

·       The failure of chromosomes pairs to separate at the centromere in meiosis.

·       Down-syndrome is a result in chromosomes pair 21. (having three: trisomy)

Non-disjunction can also occur in the sex chromosomes (x and y)

·       Turner syndrome and Klinefelter syndrome.

Inheritance of traits

·       Each version of a gene responsible for an inherited trait at the same position on the chromosomes (loci) is called an allele.

Dominant Traits: only need one copy of the allele to be visible in the physical appearance of a trait.
- represented as a capital letter.
- e.g. brown eyes represented as ‘B’

Recessive Traits: are those that can only be seen if there are two copies of the identical trait.
- represented as a lower-case letter.
- e.g. blue eyes represented as ‘b’

Genotype: is the expression of the allelic traits of an organism (the genotype is an organism’s genetic information). (example: eye colour: BB, Bb, bb).

Phenotype: is the physical appearance of an organism as determined by its alleles. (example: hair, skin.)

Zygosity = to the genetic make-up of a pregnancy.

Homozygous: (same alleles) if a person has two identical alleles, they are called homozygous for that trait e.g. brown eyed alleles.

Heterozygous: (different alleles) if a person has two different alleles e.g. brown eye and blue eye alleles.