2024 Year 12 Biology Assessment Task 1 Flashcards
advantages of models
- understand complex concepts easier
- have predictive powers (how good a model is at making predictions about what might happen in the future or in situations we haven’t tested yet)
- lead to increased understanding and future research
model
simplified representation of a complex system or concept that typically cannot be seen with the naked eye.
disadvantages of models
- inaccuracy
- oversimplification can be misleading
- lack of detail
predecessor scientists of Watson and Crick
- Phoebus Levene (1919)
- Erwin Chargaff (1950)
Phoebus Levene (1919)
Discovered:
Nucleic acids (DNA & RNA) are made of nucleotides composed of:
* A sugar molecule
* Phosphate group
* 1 of the 4 nitrogenous bases
Erwin Chargaff (1950)
Discovered:
* The relationship between Adenine (A) and Thymine (T), guanine (G) and Cytosine (C)
nucleotide structure
- phosphate group
connected to…
deoxyirobose sugar
connected to…
nitrogenous base*
scientists of Watson & Crick DNA model
- Francis Crick
- James Watson
what did Francis Crick & James Watson discover
- DNA is a double-stranded helical molecule
- Two outside sugar-phosphate backbones are held together by hydrogen bonds between parts of nitrogenous bases inside
- Each DNA molecule was a template for the other → complementary base-pairing
- During cell division, the two strands separate and the “other half” is built on each strand. DNA can replicate without changing structure. (semi-conservative)
what way does the deoxyribose sugar phosphate backbone run
5’ –> 3’
pyrimidines
single-ring structure
* thymine
* cytosine
purines
double-ring structure
* adenine
* guanine
no. of chromosomes in human cells
46
nucleosome
section of DNA coiled around histones; makes chromatin fibre; enables storage in nucleus
supercoiling
nucleosome undergoes supercoiling to make chromosomes
histone
a protein which DNA wraps around in order to condense itself and enable storage in nucleus
chromatids
identical halves of a duplicated chromosome joined @ the centromere called chromatids
homologous pairs
a maternal and paternal chromosome that contain the same genes; typically the same size and shape
homozygous
same alleles
heterozygous
different alleles
gene loci
a fixed position on a chromosome where a specific gene is found
mitosis
The process in which cells replicate their genetic material and divide to form new genetically-identical daughter cells.
interphase
- Parent cell undergoes a period of cell growth
- DNA replicated
- Centrosome (w/ centrioles) replicated
early prophase
- Chromatin start to condense into visible chromosomes
- The nuclear membrane starts to disintegrate
late prophase
- Chromatin continue to condense into double chromatids; each consisting of two sister chromatids joined @ the centromere
- Early mitotic spindle fibres form as centrioles move to opposite cell poles.
metaphase
- Chromosomes line up along the centre of the cell called the metaphase plate
- Spindle fibres (made of microtubules and proteins) connect to centromeres
anaphase
- Sister chromatids are separated by shortening spindle fibres and start to move towards cell poles
late anaphase
- Individual chromosomes continue to move towards cell poles
telophase
- Two new nuclei form around each set of chromosomes
- Condensed chromosomes unravel back into chromatins
- Spindle fibres disassemble
cytokinesis
- Cell membrane pinches @ cleavage furrow and divides cytoplasm in half resulting in two genetically identical daughter cells
importance of mitosis
- Growth
- Replacement of cells to repair damaged tissue
- Asexual reproduction
- Genetic stability → ensures chromosomes are precisely and equally distributed to each daughter cell
why does dna need to be replicated exactly
- Growth, repair, survival
- Asexual reproduction
- Genetic stability → ensures chromosomes are precisely and equally distributed to each daughter cell
- Increases an organism’s chance of reaching maturity and reproducing
polynucleotide
nucleotides are joined together to form a polynucleotide
double helix
When two polynucleotide chains line up together, the bases attach to each other like rungs of a ladder. This ladder-like structure then twists into a spiral or helix, known as a double helix because two polynucleotide chains twist together to form the helix.
codon
Made up of three base pairs and codes for an amino acid.
dna
DNA (Deoxyribonucleic Acid) is a molecule that carries the genetic instructions necessary for the growth, development, functioning, and reproduction of all living organisms. It is the universal blueprint for life, encoding the instructions to produce proteins that perform essential cellular functions and determines inherited characteristics.
shape of dna
slanted shape of molecule causes it to form a double stranded helix
gene
a short segment of DNA that carries specific bases coding specific instructions e.g. how to make a particular protein
antiparallel
polynucleotide strands are antiparallel to each other, meaning they run in opposite directions
5’ end & 3’ end
- refer to the no. of C atoms in a sugar that the phosphate binds to
- bases are read from the 5’ prime end to the 3’ prime ends
why does DNA wrap around histones?
Histones contain a large number of positively charged amino acids which allow them to bind to negatively charged phosphates of DNA
No. of chromosomes is not a measure of how complex an organism is.
true or false?
true
nitrogenous bases
- adenosine
- cytosine
- thymine
- guamine
semi-conservative
Each separated strand acts as a template for the synthesis of a new, complementary strand.
cell replication process
- helicase gradually unwinds double helix
- helicase causes strands to separate by catalysing the breaking of H bonds between nitrogenous bases to expose nucleotides
- single stranded binding proteins bind to stabilise and prevent them from joining back together
- topoisomerase prevents supercoiling of DNA
- primase makes primer on leading and lagging strands by attaching RNA bases to make a short RNA strand on the single stranded DNA
- DNA polymerase binds to the primer and adds DNA nucleotides floating in nucleus in 5’ to 3’ direction on leading strand continuously
- DNA polymerase binds to RNA primer and adds a short row of DNA nucleotides (complementary base pairing) floating in nucleus in 5’ to 3’ direction on lagging strand.
- The next primer is added further down 5’ direction.
- lagging strand constructed with okazaki fragments, replication is discontinuous
- Exonuclease removes RNA primers from both DNA strands
- DNA polymerase fills in the gaps left by the removed RNA primers with DNA nucleotides
- DNA polymerases I can correct any base pair errors by splicing the incorrect base and replacing it with the correct one
- ligase two new strands are sealed together by ligase
helicase
Causes:
* Double-stranded helix to gradually unwind
* Strands to separate by catalysing the breaking of H bonds between bases, exposing nucleotide bases
single stranded binding proteins
SSBs
- single stranded binding proteins
- single stranded binding proteins bind to separated DNA strands to stabilise them and prevent them from joining back together
topoisomerase
prevents supercoiling of DNA during DNA replication
DNA polymerase
Binds to the primer and adds DNA nucleotides floating in nucleus in 5’ to 3’ direction on leading and lagging strand.
Also proof reads and corrects DNA sequence by splicing out incorrect DNA base pairings and replacing them with the correct ones
primase
makes primer on leading and lagging strands by attaching RNA bases to make a short RNA strand on the single stranded DNA
exonuclease
removes RNA primers
genome
is an organism’s complete set of genetic information
gene
a section of DNA that codes for a characteristic
alleles
alternate forms of the same gene
genotype
refers to the genetic makeup of a particular characteristic (e.g. structure, behaviour and physiology)
–> allelles –> Bb bb BB
phenotype. what is it determined by?
- organism’s physical expression of a particular characteristic
- genotype and environmental factors
gene expression
- process in which information from gene is used in protein synthesis
- turning off and on genes
epigenetics
how environment influences gene expression at molecular level, involves chemical markers added to DNA (NOT MUTATION)
DNA replication
The process in which cells replicate their genetic material to make two identical double-stranded molecules of DNA from one double-helix molecule
polypeptide synthesis
The process in which cells build polypeptides (chains of amino acids bonded together through peptide bonds)
stages of polypetide synthesis
trancscription and translation
peptides
short chains of 2-50 amino acids
polypeptides
linear molecules made of multiple peptides
proteins
functional units made of one or more polypeptide
transcription
the process by which a complementary copy (mRNA) of a gene (DNA) is made in the nucleus
codon
- set of three bases on mRNA that codes for one particular amino acid in the polypeptide chain.
- the order of codons and the bases within them determine which amino acids are produced and in what order
categories of proteins
ENZYMES
- function: biocatalysts –> speed up biochemical reactions in the body by lowering activation –> vital for digestion, respiration, DNA replication –> denatured by changes in temp, pH, substrate conc. and inhibitors
- structure: active site that is specific to substrates
four levels of protein structure
- primary
- secondary
- tertiary
- quaternary
