Biology Unit 2 DNA, Cell division and Variation
Model answers you should know for the unit 2 exam relating to DNA and cell division
- Created by: Katie
- Created on: 07-04-12 10:56
What is the difference between a nucleotide and a
A nucleotide is a monomer(1) a nucleic acid is a polymer.
How does DNA replicate (4)
Double Helix unzips
Catalysed by helicase
Hydrogen bond break
Free DNA nucleotides in nucleus pair with complementry base pairs on both exposed strands
DNA polymerase joins nucleotides together on new strands (catalyses formation of ester bonds)
THIS RESULTS IN THE FORMATION OF IDENTICAL STRANDS
What does semi-conservative replication mean? (3)
Two new molecules are formed which are exact copies of the original(1); one of the chains in each moleculewas present in the original molecule (1); the other chain is newly synthesised fromfree nucleotides (1)
What is an allele? (1)
One alternative form of a gene
Key features of DNA
Stable so can be passed from feneration to generation
Hydrogen bonds between strands can be broken easily for DNA replication
Large so can carry lots of genetic information
Base pairs are contained ithin the sugar-phosphate backbone to prevent corruption
complimentry base pairing to allow synthesis of identical daughter cells
Important features of genetic code
It is non overlapping (specific start/stop codons)
Degenerate (ammino acids are coded for by more than one codon)
It is read in one direction
Universal- same code applies to all organisms
Definition of a gene
A section of double stranded DNA coding for a single amino acid
Definition of a locus
The position of a particular allele on a chromosome
Definition of the triplet code
Three bases in a particular sequence that code for one amino acid
Relationship between DNA and protiens
DNA has sequence of basses arrangedinto specific codons
each codon codes for one amino acid
The ribosome reads the code and reads the code and arranges the amino acids into the correct order (determined by the DNA sequence)
Peptide bonds form between amino acids to make a polypeptide chain which then fold to form the protiens specific structure
DNA and Non functional enzymes
Change in sequence of amino acids
Changes the shape of the active site
Substrate and enzyme no longer a complimentry shape
E-S complexes no longer form
DNA and phenotype
Stages of cell division (Pass Me A Tenner)
Interphase-Cell grows more cytoplasm-DNA replication-organelle replication-build up of ATP (Growth 1, synthesis and Growth 2)
Prophase- chromosomes condense nuclear envelope dissapears and spindle fibres form
Metaphase - Spindle fibres attach to chromosomes- which line up on equator of the cell
anaphase- Spindle fibres contract and pull sister chromatids apart
Telophase- New nuclear envelope forms, chromoses uncoil
Cytokinesis - Cytoplasm divides and new cell membrane forms
Purpose of mitosis
Produces IDENTICAL body cells for growth and repair
Preparing mitotic squash
Cut off tip of growing roots add aceto-orcein stain and squash
Why do you follow the steps in card 15
Root tip has fastest growing cells which divide by mitosis
Stain to make chromosomes visible
Squash to get a thin tissue layer to let enough light through for use under optical microscope
Mitosis vs Meiosis
Meiosis produces gametes- mitsosis produces other body cells
meiosis produces cells with haploid number of chromosome- mitosis produces diploid of chromosomes
meiosis produces cells that are genetically different- mitosis produces genetically identical
meiosis involves the seperation of homologous pairs- mitosis does not
Chromosome movement during meiosis
In first division homologous chromosomes line up and dseperate with one chromosome from each pair going into each daughter cell (this happens randomly and is called independent segregation)
Chromatids move apart during the anaphase of the second meiotic division
After the second division four haploid cells are formed with half the original amount of DNA as the original parent cell
Meiosis and genetic variation
Recombination of sister chromatids after crossing over during prophase of meiosis 1
Produces new combinations of alleles
Independent segregation of homologous chromosomes during anaphas of meiosis 1
This produces gametes with randomly assorted chromosome combinations
Definition of Cancer
Rapid and UNCONTROLLABLE cell division by mitosis
How do cancer treatments work
Some prevent DNA replication
Others work by preventing spindle fibres from attatching
BOTH cause inhibition of cell division causing cells to divide less rapidly
Tissue vs organ
Tissue is a group of similar cells organised to carry out a specific function
Organ is a group of tissues co-ordinated to perform a variety of functions
What is cell differentiation
The process of a cell becoming specialised in structure to carry out a specific function
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