Unit 1 Biology

• what is dna?


  deoxyribonucleic acid is the molecule that determines the characteristics of most living things on earth.
• describe DNA's structure


  double-helix, ie. twisted rope ladder

  -uprights of the ladder are made up of alternating phosphate and sugar groups

  -rungs are nitrogen rich bases paired up.

  
• what are the smaller molecules which make up DNA?

  nucleotide
• what is a nucleotide

  the building blocks of DNA, comprised of deoxyribose sugar, a phosphate group and a nitrogen rich base.
• what are the four nitrogen rich bases?

  Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
• what is complementary base pairing?

  when nitrogen rich bases (A,T,G,C) pair in a complementary way, due to their different chemical structures and shapes which only complement one other base.

  
• what are the complementary base pairs?

  adenine (A) pairs with thymine (T)

  cytosine (C) pairs with guanine (G)
• what are chromosomes?


  chromosomes are long, thread like structures found in the nucleus made up of DNA and proteins, contains genetic information in the form of genes.

  
• what is the human chromosome number?

  46, 23 from your mother and 23 from your father.
• do all organisms have the same number of chromosomes?

  no, the number varies depending on organism
• how many sex chromosomes are there, and what do they do?

  -2 sex chromosomes, chromosomes that determine the sex of an individual, whether they are male or female.

  -in humans, they are the 'x' and 'y' chromosomes, in females (XX) in males (XY)
• what are autosomes


  the other 22 pairs of chromosomes, which aren't sex cells.
• what are homologous chromosomes

  paired chromosomes with genes for the same traits arranged in the same order, with a centromere at the same position.
• where else is DNA stored other than the chromosomes in the nucleus?

  cells have some DNA in the mitochondria

  plant cells have DNA in the chloroplasts

  this DNA occurs as circles, rather than long strings.
• what is a gene


  a section of DNA arranged along the chromosomes that carry the code for a particular characteristic, eg. eye colour/hair colour.
• difference between one gene and the next

  order of bases along the DNA strand

  number of bases in that section of DNA
• what is the genetic code?

  the order of bases along the DNA strand
• what does the genetic code do

  specifies which amino acids will be used to build a protein
• name the 3 types of proteins

  -structural

  -enzymes

  -regulatory
• examples of structural proteins


  -collagen (found in tendons and ligaments)

  -keratin (found in skin, hair, nails, scales, feathers)
• examples of enzyme proteins

  -amylase (which helps digests starch)

  -lactase (which helps digest lactose, the sugar in the milk)
• examples of regulatory proteins

  -growth hormone (stimulates growth and cell reproduction)

  -insulin (which controls blood glucose levels)
• what is determined by genes


  unique characteristics of organisms are determined by genes
• how many copies of a gene does an individual have?

  2 copies of each gene (46) , one from each parent, known as homologous chromosomes
• what is replication?


  the process of copying DNA, by which a double stranded DNA molecule is copied to produce two identical DNA molecules, usually ocurring before cell division. in single cell organisms (prokaryote), occurs in the cytoplasm, in multicellular organisms (eukaroye) takes place in the nucleus.
• first step of replication

  strands of double helix seperate/unwind/unzip from each other, leaving the nitrogen rich bases (ATCG) exposed.

  
• within the nucleus, there are...


  individual nucleotides that are not yet part of DNA chain

  
• second step of replication

  -nucleotides pair up with the exposed bases following complementary base pairing

  -sugars and phosphate molecules bond with neighbouring nucleotides and new strands of DNA are formed

  
• third step of replication

  two identical DNA molecules form, each identical to the parent DNA

  
• what happens to chromosomes after replication?

  each replicated chromosome now has two identical DNA molecules, called chromatids

  
• what is a chromatid


  one half of a duplicated chromosome

  
• what is mitosis


  a type of cell division which produces two daughter cells that are identical to the parent cell, type of cell division involved in growth and repair of the body. occurs in somatic cells, which are all cells not required in the production of gametes/meiosis.
• what is meiosis


  the type of cell division which produces four haploid daughter cells, which are cells that have half the number of chromosomes of the parent cell. meiosis produces gametes (sperm cells & ova/eggs). meiosis only occurs in reproductive cells, such as sperm and egg cells in humans.
• what is the first stage of mitosis

  interphase: chromosomes replicate to have two chromatids

  
• what is the second stage of mitosis

  prophase:

  -membrane surrounding the nucleus breaks down, DNA condenses

  -replicated chromosomes and their chromatids become visible, spindle fibres form

  
• what is the third stage of mitosis

  metaphase:

  -replicated chromosomes line up on the spindle fibres along the equator (middle) of the cell

  
• what is the fourth stage of mitosis

  anaphase:

  -the chromatids seperate at the centromere as they are being -pulled by the contracting spindle fibres and move to opposite poles of the cell

  
• what is the fifth stage of mitosis

  telophase:

  -new cell membrane form, two nuclei form

  -each with the same number of chromosomes as the parent cell, two identical daughter cells form

  
• what is diploid number


  the number of chromosomes present in a human body/diploid cell (46), represented by 2n; meaning two sets of autosomes + chromosomes
• what is haploid number


  the number of chromosomes within a gamete (23) (eggs and sperm), represented by 2n