Year 12 Biology Module 5: Heredity

What is the difference between asexual reproduction and sexual reproduction?

Asexual reproduction involves the production of offspring from one parent only while sexual reproduction involves two parents with the union of a gamete from each parent.

Asexual reproduction is ___________________ when a parent organism is ________________ to its environment and being able to clone many copies of itself in a relatively _______ period of time uses less __________ than sexual reproduction. This means it can __________ spread into a less populated area.

advantageous

well-suited

short

energy

rapidly

What are the five types of asexual reproduction?

1. Spores

2. Binary fission

3. Budding

4. Vegetative propagation and fragmentation

5. Parthenogenesis

DNA

deoxyribonucleic acid

Alleles

Different forms of a gene

Phenotype

physical characteristics of an organism expressed from the gene information of a cell

Genotype

An organism's genetic makeup, or allele combinations.

Homozygous (purebred)

An organism that has two identical alleles for a trait

Heterozygous (hybrid)

An organism that has two different alleles for a trait

What does the DNA in prokaryotes look like?

prokaryotes consist of one very long circular DNA molecule

What does DNA look like in eukaryotes?

consists of several linear molecules with associated proteins

What does the backbone of DNA consist of?

sugar molecules (deoxyribose sugar) linked to phosphate groups

What forms the 'rungs' of the ladder of DNA?

Nitrogenous bases

What are the nitrogenous bases?

Adenine, Thymine, Guanine, Cytosine

What is chromatin and when is it visible?

When a eukaryotic cell is not dividing chromatin chromatin exists in its dispersed form as a mass of very long thin fibres not visible with light microscope

What are histones?

Special round proteins responsible for chromatin formation.

What are nucleosomes?

a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.

What is polypeptide synthesis?

Involves a type of nucleic acid called RNA which is a single strand of nucleotide bases with ribose sugar and the nitrogen base uracil. Two type of RNA are involved; messenger RNA (mRNA) and transfer RNA (tRNA) and there are two steps; transcription and translation

At the beginning of protein synthesis __________________________ binds to the promoter part of the gene that is going to be transcribed and the DNA '__________' with hydrogen bonds between nitrogenous bases breaking. One side is called the '_______' strand with the DNA code to make the protein.

RNA polymerase

unzips

sense

What is a polypeptide?

A chain of amino acids --> a polymer of amino acids that have a specific function. We also call them proteins.

What are exons and introns?

EXONS: coding sequences → will result in a polypeptide after translation.

INTRONS: Non-coding sequences → will not result in polypeptide, need to be removed.

What is translation?

Involves the synthesis of a polypeptide chain from a mRNA base sequence at a ribosome in the cytoplasm

What are ribosomes?

Site of protein synthesis. Made of ribosomal subunits and a strand of ribosomal RNA (rRNA) and proteins.

What is the process of transcription/unzipping?

Double strand of DNA unwinds. RNA moves along strand linking complementary nucleotides together to form mRNA. The mRNA then moves from the nucleus into the cytoplasm.

What is the process of translation?

mRNA strand binds onto ribosome. tRNA binds to mRNA within the ribosome. The ribosome moves along the strand linking the amino acids, forming a polypeptide chain. When a stop codon is reached, the chain is released into the cytoplasm.

How could a mutation in DNA affect polypeptide production?

A mutation in DNA changes the bases, which means that the amino acids making up the polypeptide are different. This means a different polypeptide is formed.

How could a change in a polypeptide affect cell activity?

A change in polypeptide leads to change in protein structure. If the protein is an enzyme, the cellular reaction it is involved in won't happen.

Outline the function of RNA

There are different specific tRNA molecules for each amino acid. They bring their amino acid into the ribosome (rRNA) where they bind to specific mRNA bases (codons) and mRNA takes its code directly from DNA.

Describe the roles of DNA and RNA in an application of biotechnology

Recombinant DNA technology is used to produce insulin for diabetics. The relevant cDNA is produced by reverse transcribing RNA. This cDNA codes for the protein insulin. The cDNA is then spliced into the DNA of a bacterium. The incorporated DNA is transcribed to mRNA ad translated using tRNA. The result is the protein insulin.

Outline the steps in the formation of a functional enzyme from polypeptide chains

The polypeptide chain folds up into a specific three-dimensional shape. Folded chains can then link together in a specific way. These processes shape the protein or enzyme. The shape of the enzyme defines the substrate it will act on. Acting on a specific substrate is the function of the enzyme.

Explain why transcription and translation result in different products

Transcription is the copying of DNA into mRNA. This takes place in the nucleus. So that the DNA can be copied, a pool of nucleotides - A, U, G and C - are linked together to form the complementary strand of mRNA. Translation is the formation of a polypeptide according to codons in the template mRNA. This takes place in the cytoplasm where the ribosomes are located. The polypeptide is formed by linking amino acids with peptide bonds. A pool of amino acids for this purpose is found in the cytoplasm.

What is a phenotype?

the detectable or expressed property(ies) or traits of an organism. It is the result, not only of genotype but of its environment as well

Explain the processes that could result in differences in appearance of offspring.

Random changes or mutation of the genes in the duplication of the chromosomes when undergoing the first stages of replication process in the production of gametes.

Changes in the chromosomes resulting from crossing over, where exchange of genetic material happens randomly between chromosomes which occurs in the first stages of meiosis resulting in unique gametes.

Random segregation of chromosomes in the later stages of meiosis resulting in unique gametes.

What is the point of reproduction?

It is an essential feature of all living organisms. If organisms do not reproduce, their species dies. The point is the continuity of species.

All organisms, except ____________ and ______________ have sexual reproduction.

Bacteria

Archaea

What are the advantages and disadvantages of sexual reproduction?

A: Increases genetic variation.

D: requires more energy and time

What are the advantages and disadvantages of asexual reproduction?

A: can produce large numbers of offspring quickly to take advantage of a sudden or temporary increase in some environmental resource such as food. Uses less energy.

D: by producing genetically identical offspring, there is less variation in the population. If an environmental change occurs, a low-variation species is at risk of extinction.

Parthenogenesis

Asexual reproduction in which females produce offspring from unfertilized eggs.

What are your body cells and sex cells called?

somatic cells

gametes

Explain the reproductive strategies of placental mammals, Marsupial mammals, and monotreme mammals.

placental mammals: females carries fetus inside her body, nourished through placenta until fully developed (human)

Marsupial mammals: fetus born at an early stage, complete their development in external pouch while suckling (kangaroo)

Monotreme mammals: female lays eggs with leathery shells then protects them and feeds the young with milk (platypus)

Distinguish between zygote, blastocyst, embryo and foetus

Zygote is the first stage after fertilisation, the diploid cell that results from fusion of a haploid egg and sperm.

Blastocyst is the next stage when the morula has divided by mitosis into many smaller cells that are organised into two layers.

Embryo is the next stage until major organs have developed.

Foetus: is the final stage of development when all of the major organs have developed. This stage lasts until birth.

Where would you find a follicle and what is its function?

A follicle is a group of cells in the ovary that surround an oocyte as it matures. The follicle provides protection and nutrition to the egg, then ruptures to release the egg (ovulation)

deoxyribonucleic acid (DNA) is .......and where is it found?

the genetic material that encodes for all proteins that allow a cell to function.

Found in the nucleus of eukaryotic organisms and the nucleoid of prokaryotic organisms.

What is a nucleotide?

Nitrogenous base + sugar (ribose or deoxyribose) and phosphate group

There are two hydrogen bonds between _____________ and _____________ and three hydrogen bonds between ____________ and _____________

adenine

thymine

cytosine

guanine

Gene variants are called

alleles

Cell theory states

All living things are made up of cells, cells are the basic units of structure and function in living things, new cells are produced from existing cells

Why does DNA need to replicate exactly?

An organism's genetic code contain instructions for every feature of that individual (how the function and physical features), when a cell divides, it is vital that the DNA passed on to each daughter cell is an exact copy, so that each generation contain the same genetic instructions.

Why do cells replicate?

growth and development, maintenance and repair

What are the three main parts of the cell cycle?

interphase, mitosis, cytokinesis

Explain the three stages of interphase

Gap 1: cellular contents (excluding the chromosomes) are duplicated.

Synthesis: DNA replicates

Gap 2: enzymes check the duplicated chromosomes for error, making any needed repairs. Cell synthesises, materials such as proteins, needed for division.

Four steps of mitosis are

prophase, metaphase, anaphase, telophase

Centromere

point of a chromosome where sister chromatids are joined

Centrioles

pair of tiny cylindrical organelles composed of a bundle of microtubules, assemble spindle fibres

Interphase

Chromosomes are not visible, replication occurs, centrioles replicate.

Prophase

Chromosomes condense and become visible, centrioles move to opposite sides of the nucleus to form the poles, spindle fibres begin to form.

Metaphase

Centromeres attach to spindle fibres and align at the equator between the poles.

Anaphase

Spindle fibres contract, chromosome pairs separate and are pulled toward opposite poles.

Telophase

Nuclear membrane reforms around two sets of chromosomes, spindle fibres disappear, chromosomes become longer and thinner.

Cytokinesis

Division of the cytoplasm to form two separate daughter cells

Meiosis prophase 1

chromatin condenses into chromosomes, spindle apparatus forms, nucleoli and nuclear membrane disappear; homologous chromosomes (one from mom and one from dad) come together and intertwine (synapsis); where crossing over occurs

Metaphase 1

Paired homologous chromosomes line up across the center of the cell (orientation is random between pairs)

How does meiosis result in genetic variation?

Crossing over: homologous chromosome pairs exchange genetic material at random (at different points)

Random orientation of homologous pairs: metaphase I maternal and paternal pairs line up randomly

Meiosis only occurs where?

in the male and female gonads (ovaries/testes) from germ cells

Chromatin

DNA tightly coiled around histones (proteins)

What is the Watson and Crick model?

Cellular DNA is a double helix held together by hydrogen bonds between bases. The strands run antiparallel

The (double ringed) purine bases are

Adenine and Guanine

The (single ringed) pyrimidine bases are

Thymine and Cytosine

Bases attach to ________ in DNA and RNA

sugars

There is always a ___________ between two sugars on the backbone

phosphate

If deoxyribose is an arrow then the oxygen is a point and it points from ______ prime to ______ prime.

three

five

RNA is the other nucleic acid. The differences between DNA and RNA are:

- RNA is single strand

- RNA polynucleotide strands are usually much shorter

- sugar-phosphate backbone has a ribose sugar

- Uracil replaces thymine

- three main forms: messenger RNA, ribosomal RNA and transfer RNA

What is DNA replication?

The production of two identical double-stranded molecules of DNA from the original double helix molecule.

Step 1 of DNA replication:

An enzyme called helicase causes the helix to progressively unwind and the strands to separate at the replication fork. Hydrogen bonds between base pairs break easily.

Step 2 of DNA replication:

There is a bank of free nucleotides stored in the nucleus.

An enzyme called primase initiates the first stage of synthesis.

The free nucleotides pair up with each template strand (using complementary base pairing rules) to make new strands.

The replication process proceeds from the 5' towards the 3' end of the DNA.

Step 3 of DNA replication:

As each complementary strand forms, replication fork moves along and the completed pairs of DNA strands rewind into double helix coils under the control of other enzymes.

Each double helix coils around histone proteins and reforms chromosomes with twice as much DNA with two sister chromatids joined at the centromere ready to undergo cell division.

How is the lagging strand replicated?

DNA polymerase must work in the direction 5' to 3' so synthesis is achieved by forming short lengths (Okazaki fragments) of DNA that are later joined together by the DNA ligase enzyme.

Assess the effect of the cell replication processes on the continuity of species.

The inheritance of characteristics from ancestors to currently living organisms relies on the passing on of consistently accurate genetic information, so that adaptations can arise.

Accurate DNA replication = genetic stability

Mutation = genetic variation

Genetic continuity is dependent on two things:

1. during mitosis, the resulting daughter cells must have the same number of genes as the original cell

2. when two sexually reproducing organisms breed, the resulting offspring must have the number number of genes as the parent organism and variations in these genes must not be extremely detrimental or lethal

Explain genetic stability on a genetic level and species level.

Stability arises when chromosomes are replicated accurately and give rise to identical daughter chromosomes.

Successful and desirable traits must be passed on, along with some random errors. This allows species to evolve if environmental change occurs.

Mechanisms that result in genetic continuity

- consistent replication prior to cell division

- an orderly distribution of chromosomes when cells divide/gametes form

- fertilisation methods that ensure that individuals breed successfully

- methods to ensure embryo survival (large numbers, nourishment, protection)

- natural selection so that the fittest survive and reproduce and pass on genes.

Mechanisms that result in genetic variation

- mutation

- crossing over and independent assortment during meiosis and random fertilisation of gametes

What genetic errors threaten the continuity of species (provide examples)

mutations in DNA are temporary and correct by enzymes responsible for DNA repair, people who have a reduced ability to repair DNA:

- more susceptible to some cancers

- accelerated aging giving rise to neurodegeneration

Compare DNA in prokaryotes and eukaryotes

Eukaryotic DNA:

- contained in nucleus

- linear

- in chromosomes

- packaged with proteins called histones forming units called nucleosomes

- large amount of DNA

Prokaryotic DNA

- present in the centre of cell called 'nucleoid' (not bound by membrane)

- circular

- one copy

- may contain plasmids (small circular DNA with some genes)

- no histones

Gene

A section of DNA that contains instructions for making a protein or RNA molecule

Protein structure: ________ _______ that form ______________ which then form __________.

amino acids

polypeptides

proteins

DNA transcription

the formation of mRNA strand complementary to the DNA nucleotide sequence that specifies the amino acid sequence for a particular polypeptide.

Only one strand of DNA is used as a template for transcription. This strand is called the ......

non-coding strand or template strand.

DNA transcription has three basic steps:

1. Initiation

2. Elongation

3. Termination

Step 1 in DNA transcription (initiation)

RNA polymerase binds to the DNA at a specialized sequence called a promoter. In eukaryotes the promoter region is coded by the sequence of bases TATAAA (TATA box)

Step 2 in DNA transcription (elongation)

DNA unwinds and RNA polymerase reads the template strand adding nucleotides to the 3' end of the growing chain.

Step 3 of DNA transcription (termination)

terminator sequence is found close to the ends of noncoding sequences, there are inverted repeat sequences that are transcribed, they can then fold back on themselves in hairpin loops, causing RNA polymerase to pause and release the transcript (mRNA)

Before the primary mRNA can be translated mRNA maturation occurs (only in eukaryotes):

1. capping: addition of a molecule called CAP at the 5' end of mRNA

2. polyadenylation: addition of A chain at 3' end (poly-A-tail)

3. RNA splicing: removal of introns

Translation occurs in the __________, an organelle present in ALL cells (pro and eukaryotic) and uses ______________ for the direct translation from mRNA to ___________ _________.

ribosome

transfer RNA

amino acids

every three bases of mRNA are called ________

codon

Where are ribosomes and what are their function?

Free in the cytoplasm or attached to endoplasmic reticulum.

Catalyse translation process.

tRNA has ______ bases at one end called ____________ which corresponds to a __________ in mRNA.

Holds the ________ ______ on 3' end and there is one tRNA per every _______ ______.

three

anticodon

codon

amino acid

amino acid

The genetic code is said to be _____________ because more than one RNA codon can code for the same __________ ________.

degenerate

amino acid

The degeneracy of the code acts as a buffer as......

a mutation of a single base may not necessarily lead to a change in the amino acid produced or the protein then produced.

tRNA molecules transfer _________ ______ from the ____________ to the ___________.

amino acids

cytoplasm

ribosomes