CELLS

DNA

Deoxyribonucleic acid; provides instructions for cells to construct specific proteins.

Nucleotide

The monomer of DNA, made of a phosphate group, deoxyribose sugar, and a nitrogenous base.

Double Helix

The structure of DNA made of two antiparallel strands twisted around each other.

Sugar-Phosphate Backbone

Strong phosphodiester bonds form the sides of the DNA ladder.

Nitrogenous Base Pairs

Held together by weaker hydrogen bonds in the centre of the DNA molecule.

Adenine (A) pairs with Thymine (T)

2 hydrogen bonds.

Cytosine (C) pairs with Guanine (G)

3 hydrogen bonds.

Gene

A sequence of DNA that codes for a protein.

Chromosome

Long strands of DNA wrapped around histone proteins; carries many genes.

Telomere

Protective repetitive base sequences at chromosome ends.

Centromere

Holds two sister chromatids together.

Sister Chromatids

Identical strands formed by DNA replication.

Autosome

One of the 22 pairs of chromosomes that are not involved in determining sex.

Sex Chromosome

The 23rd pair of chromosomes determining biological sex.

Female Sex Chromosome Pair

XX.

Male Sex Chromosome Pair

XY.

Relationship between Genes, DNA, and Chromosomes

Genes are made of DNA, DNA is coiled into chromosomes, and genes are located at specific loci on chromosomes.

Somatic Cell

Body cell (e.g. skin, muscle); diploid with 46 chromosomes.

Gamete

Sex cell (sperm or egg); haploid with 23 chromosomes.

Diploid (2n)

Cell with two sets of chromosomes (46 in humans).

Haploid (n)

Cell with one set of chromosomes (23 in humans).

Purpose of Cell Division

1. Growth and development; 2. Cell replacement; 3. Asexual reproduction.

Mitosis

Nuclear division that produces two identical diploid somatic cells.

Prophase

Chromosomes condense, spindle forms, nuclear membrane breaks.

Metaphase

Chromosomes line up in the centre.

Anaphase

Sister chromatids separate to opposite poles.

Telophase

Nuclear membranes reform.

Cytokinesis

Cytoplasm splits, forming two identical cells.

Meiosis

Cell division in gametes producing four genetically different haploid cells.

Crossing Over

Exchange of genetic material in Prophase I.

Independent Assortment

Random arrangement of chromosomes in Metaphase I.

Nondisjunction

Failure of chromosomes to separate during meiosis, causing aneuploidy.

Trisomy

A condition where an individual has three copies of a chromosome (e.g. Down Syndrome = ****** 21).

Monosomy

A condition where an individual has only one copy of a chromosome (e.g. Turner Syndrome).

Karyotyping

Visual layout of chromosomes to check number, size, and structure.

Down Syndrome

Genetic Condition: Extra chromosome 21.

Genetic Condition: Turner Syndrome

Only one X chromosome in a female.

Genetic Condition: Klinefelter’s Syndrome

XXY in males.

Genetics

The study of heredity and how traits are passed on.

Gregor Mendel

Discovered basic inheritance using pea plants; father of genetics.

Dominant Trait

Represented by a capital letter; expressed if present in the genotype.

Recessive Trait

Represented by a lowercase letter; only expressed if both alleles are recessive.

Genotype

The alleles present for a trait (e.g. BB, Bb, bb).

Phenotype

The physical expression of a genotype (e.g. brown eyes).

Allele

A different version of a gene (e.g. B for brown eyes, b for blue eyes).

Homozygote

Two identical alleles at a gene locus (BB or bb).

Heterozygote

Two different alleles at a gene locus (Bb).

Homologous Chromosomes

Pairs of chromosomes with the same genes at the same loci.

Monohybrid Cross

A genetic cross involving one trait to predict genotype and phenotype ratios.

Punnett Square

A grid used to determine possible allele combinations in offspring.

Sex-Linked Traits

Traits controlled by genes on sex chromosomes, usually the X.

Colour Blindness

X-linked recessive trait; expressed in males who inherit the affected X.

Haemophilia

X-linked recessive disorder; more common in males.

Interphase

The longest phase of the cell cycle, including three stages

G1 (Gap 1)

Cell grows, organelles duplicate, proteins for DNA replication are made.

S (Synthesis)

DNA replication occurs, chromosomes duplicate to become double-stranded.

G2 (Gap 2)

Cell grows again, and proteins are synthesised in preparation for mitosis.

G1 Checkpoint

Checks if the cell is the correct size, has enough proteins, and undamaged DNA.

G2 Checkpoint

Ensures DNA was correctly replicated and the cell is ready for mitosis.

G0 Phase

A resting stage where cells do not divide.

Binary Fission

The process by which prokaryotic cells (e.g. bacteria) divide

binary fission steps

• DNA replication

• Elongation

• Septum formation

• Cell division

cell definition

the basic functional unit of life

cell theory

1. all living things are made up of cells

2. all cells come from pre-existing cells

3. cells are the base units of structure and function

prokaryotic

• has no true nucleus

• no membrane bound organelles

• very small

eukaryotic

• has a true nucleus

• has a membrane bound organelle

• larger

cell wall

provides strength, support and protection for cells

cell membrane

controls what enters and exits the cell

nucleus

controls cellular activities like cell division

chloroplast

site of photosynthesis

mitochondria

site of aerobic respiration

ribosomes

creates proteins

telaphase

the cell membrane pinches in starting to form two new cells

Structure that’s common to all cells

cell membrane

The area spindle fibers join during cell division

centromere

advantages of S-shaped spine

more efficient vertical stance to allow them to walk further

advantages of larger forum magnum

more central more efficient vertical stance to allow them to walk further