Cell Replication Flashcards
DNA
Deoxyribonucleic acid: a chemical found in the nucleus of each of our body cells – a code that your body uses as its instructions
Gene:
Gene: a distinct sequence of nucleotides forming part of a chromosome – which determines the amino acids it will synthesize which determines its function
Chromosomes
Chromosomes: structures within cells that contain a person’s genes.
Watson and Crick model
- nucleotide is made of a phosphate root, attached to deoxyribose sugar and nitrogenous base (ACTG)
- sugar phosphate backbone
- the ratio of A:T and G:C bases are 1:1
- A = T, triple bond for B-G
- set distance between strands - means A can only bond with T and G with C
- antiparallel: run in opposite directions
Structure of a chromosome
- Each chromosome is made up of chromatin fibres
- Each chromatin fibre is a tight wound supercoil
- Each supercoil is made up of structures (a chain of beadlike structures called ‘nucleosomes’)
- Each nucleosome consists of DNA wound around histones
DNA
Double-stranded molecule (helix shape)
Made up of nucleotides, with nitrogenous bases: adenine, thymine, guanine and cytosine
Location: main chemical in the nucleus, small amount found in mitochondria and chloroplast.
Role: chemical code used in protein synthesis and responsible for transmitting inherited traits from one cell to another.
RNA
Single stranded
Made up of nucleotides, with base ‘uracil’ replacing thymine
Location: small amount in nucleus, large amount in cytoplasm (associated with ribosomes)
Role: used in the process of protein synthesis. Includes: messenger (mRNA), transfer (tRNA), ribosomal (rRNA)
RNA replication diagram
- DNA topoisomerase - relaxes DNA from supercoiled state. dna helicase unwindes the double helix
- DNA helicase uses ATP to catalyse the breakage of weak hydrogen bonds between nitrogenous bases
- single stranded binding proteins (SSBs) bind to newly separated single stranded DNA to stabilise it
- for synthesis to be started, a short strand of RNA (RNA primer) needs to be made and attached to the DNA by primase
- DNA polymersase III adds nucleotides to unzipped DNA to synthesise new strands. polymerase 1 and 2 will backtrack and edit any mistakes (missed mistakes = mutations)
- DNA ligase seal the two new strands back together
Cell cycle
G1: cell growth – metabolic changes prepare cell for division
Synthesis: each of the 46 chromosomes are duplicated
G2: enzymes in the cell check the duplicated chromosomes and cytoplasmic materials prep for division
mitosis and meiosis
Mitosis: production of diploid cells for growth and prepare
Meiosis: production of haploid cells (gametes) for sexual reproduction
Interphase 1
- Membrane is intact.
- DNA replication occurs (not visible), giving double the amount of DNA
Early prophase 1
- DNA chromatid condense (coils up) now visible under microscope.
- Original and copy pair up and attach via a centromere. Each side is called a chromatid, together called a chromosome.
- Genetic variation: homologous chromosomes pair up (consist of two similar chromosomes – one maternal and other paternal in origin). Their replicated chromatid is attached.
- Genetic variation: crossing over / synapsis
The inside chromatids of homologous chromosomes cross over and swap genes. The chromatids of homologous chromosomes now contain different combinations of genes. Crossing over increases variation – no two chromatids are identical. The arms of the pair of homologous chromosomes are called bivalent. The points at which they meet are called chiasmata.
Metaphase 1
- Chromosomes (homologous) line up along the equator
- Genetic variation: independent assortment
The pairs of homologous chromosomes line up at the equator independent of each other. The maternal chromosomes may be on the right or left for each pair. There are 223 different combinations for how 23 pairs of chromosomes can sort themselves.
Anaphase 1
- Spindle fibres contract, pulling the homologues to separate poles of the cell
Telophase 1
- Spindle fibres disappear
- Nuclear membrane form around each set
