Biology Unit 4

DNA

molecule that contains genetic instructions for an organism.

prokaryotes

singular, circular chromosome that exists in a cytoplasm

eukaryotes

Found in nucleus where the DNA wound around proteins that forms chromosomes. Single chromosome found in mitochondria and chloroplasts.

3 components of a nucleotide in DNA

5 carbon sugar, phosphate group, 4 bases- adenine, thymine, guanine, cytosine

Helicase enzyme

the enzyme unzips DNA creating two single strands of DNA

topoisomerase enzyme

The “muscle” of the operation, relaxing the super coiled nature of DNA

Primase enzyme

This “primes” the DNA creating a starting point for DNA polymerase

DNA polymerase enzyme

the builder enzyme works hard, copying new strands of DNA by adding nucleotides

exonuclease enzyme

the enzyme cuts out RNA primers and DNA that needs fixing

ligase enzyme

this sticks the DNA strands together

steps of DNA replication

unzipping, stabilising, priming, building and extending, replacing, gluing, proofreading

Steps of spermatogenesis

spermatogonium, primary spermatocyte, secondary spermatocyte, spermatids, spermatoza

Steps of oogenesis

oogonium, primary oocyte, secondary oocyte/ first polar body, ootid/ second polar body, ovum

gene

each gene consists of a segment of DNA with nucleotide bases in a specific sequence and forms part of a chromosome

genome

complete set of nucleotide sequences encoded in DNA

allele

alternative form of gene

locus

fixed position on a chromosome that is occupied by a gene or allele

Introns vs extrons

introns are sections of mRNA that dont make protein and removed from the strand of mRNA. Extrons are sections of mRNA that make protein and spliced with other extrons to make chain of mature mRNA

telomers

stretches of DNA at the end of the chromosome that protect genetic information by ensuring it doesn’t fray or stick to other chromosomes

two steps of protein synthesis

translation and transcription

Translation

Code is changed from nucleic acid language to amino acid language

transcription

RNA “writes down” the DNA code

messenger RNA (mRNA)

transcribes DNA code

ribosomal RNA (rRNA)

primary component of ribosome

transfer RNA (tRNA)

carries amino acid to position during translation

Steps of transcription

DNA strands separate

one side serves as a template

mRNA transcribed from DNA template

mRNA introns spliced

mRNA exists in the nucleus

Translation steps

mRNA attaches to ribosome in cytoplasm

tRNA carries amino acid base pairs with mRNA codons

amino acids bond to form polypeptide chain

codon

3-base word on mRNA that codes 1 amino acid

genotype

set of genes in DNA responsible for a particular phenotypic trait

phenotype

physical expression of the trait as a protein or observable characteristic

gene expression

process where information is stored in a gene is used to synthesise a functional gene.

Primary protein structure

linear sequence of amino acids that make a polypeptide chain

secondary protein structure

repeated patterns of folding of the protein backbone.

tertiary protein structure

overall folding of polypeptide chain into 3D.

Quaternary protein structure

occurs when protein is made up of two or more polypeptides and descibes how different subunits are arranged.

HOX genes

group of homeotic genes that decide what body part will grow where.

SRY genes

key gene that starts male development and is found in the Y chromosome (only in males)

causes of gene mutations

DNA replication errors, cell division errors and damage by mutagens

Heterozygous

two different alleles (Tt)

Homozygous

same alleles (TT or tt)

dominant gene

describes a trait that is expressed in an heterozygous individual (T)

Recessive gene

a trait that is hidden in a heterozygous individual (t)

autosomal

a chromosome that is not a sex chromosome. people have 22 pairs in each cell with 2 sex chromosomes.

autosomal dominant

a pattern of inheritance in which an affected individual has one copy of a mutant gene and one normal copy on a pair of autosomal chromosomes and the mutant gene is expressed.

autosomal recessive

a pattern in inheritance where an affected individual must have two copies of a mutant gene for it to be expressed.

gene therapy

insertion of genes into cells and tissue to treat a disease where a defective allele is replaced with a functional one. it uses DNA cloning.