biology quiz

the nucleus

The nucleus contains instructions for our cells which are carried in our DNA

Determines what a cell will become, what its function will be, when it will grow and divide, and when it will die

dna

deoxyribonucleic acid

dna structure

DNA is a long two stranded molecule that looks like a twisted ladder

The two sides of the DNA wrap around each other to give it a double helix structure

dna storage

The sides of the ladder are made up of sugar and phosphate

The steps of the ladder are made of four nitrogen bases

(A) - (T)

(C) - (G)

Adenine - Thymine

Cytosine - Guanine

The number of bases and their order can be different within DNA molecules of different individuals

Bases in DNA always join in a specific way

In humans a single DNA molecule can be several million base pairs in length

DNA is stored in the nucleus in the form of chromatin

Each strand of chromatin contains proteins and one DNA molecule

When cells grow the DNA uncoils and helps make proteins

When the cell is ready to divide each strand of chromatin coils into a X shape structure called a chromosome

Within the human nucleus there are 46 chromosomes that are arranged into 23 pairs

One pair of chromosomes determines the sex

Female

XX

Male

XY

Genes are small segments found at specific places on a chromosome

Genes store the information needed to create thousands of proteins that your body needs

Each chromosome contains thousand of genes and therefore can create thousands of different proteins

Each cell contains all of our genetic information stored within our 46 chromosomes

Only specific sections of the DNA is read to create the needed proteins for the body

The formation of specific proteins allow cells to become specialized to allow them to carry out particular functions which is why cells in our eyes are different from cells in our skin

Specialized cells come together to make tissue and tissue comes together to make organs

Enzymes are specialized proteins that speed up the chemical reactions that happen in our bodies

Digestive enzymes help break down our food into nutrients

Hormones are proteins that act as messengers

The process of DNA creating an exact copy of itself is called replication

A cell replicates all of its DNA in one hour (before dividing) and there is often only mistake in one billion nucleotide pairs

A nucleotide is a building block of DNA and is made up of the phosphate, sugar, and the base

The base is attached to the sugar

For the pairs to match up in making the other strand of DNA and making mRNA, we use enzymes

There are three types of gene mutations

Gene mutations occur when the order of nitrogen base pairs change within a specific gene

Deletion

one base is missing

Thmanranforthebus

Thm anr anf ort heb us

Addition

an extra base is added

Themanrranforthebus

The man rra nfo rth ebu s

Substitution

one base is substituted for another

Teemanranforthebus

Tee man ran for the bus

DNA cannot leave the nucleus so it copies its message creating mRNA (messenger RNA)

When making mRNA: A - Uracil (U) C - G

Sequences are read three bases at a time which is called a codon

A sentence without spaces is like a sequence of bases

A mutation that benefits an organism is known as a positive mutation

Millions of people around the world are infected with HIV and will develop AIDS. Some individuals carry a mutated gene that produces a protein that prevents HIV from infecting the individual. These individuals have a positive mutation and are resistant to the HIV virus.

Mutations that are harmful to an individual are known as negative mutations.

Sickle cell anemia is caused from the substitution of an A base for a T base. This mutation changes the shape of red blood cells causing it to be harder to carry oxygen through the body. The blood cells may also block blood flow.

Mutations that do not affect the survival rate of an individual are known as a neutral mutation.

Most often, errors in the base sequence of DNA do not affect the organism. Example: birthmarks

Substances or factors that can cause DNA mutations are called mutagens

Cigarette smoke, radiation from X rays or UV rays, pollutants, household chemicals

The most common way to treat the effects of negative mutations is though drugs or surgery

Researchers are testing new techniques called gene therapy

Mutated genes are replaced with healthy genes

Inactive viruses are often used to carry healthy DNA into cells with mutated DNA

Cells continue to grow and divide through an individual's life

Throughout the cell cycle there are checkpoints that monitor the cell activities

Proteins monitor these activities and then send the information to the nucleus which will instruct the cell to divide or not

The cell will not divide if there are not enough nutrients, the DNA has not replicated, or the DNA is damaged

A carcinogen is a substance that causes cancer and may be a result of a mutation

If a mutation occurs that affects the protein controlling the checkpoints of the cell and the cell may divide uncontrollably

Cancer is the name given to the cells that divide uncontrollably

Healthy cells will grow in a single layer until they receive a message from neighboring cells to stop dividing

Cancer cells do not respond to the message sent from neighboring cells

The DNA in our cells is used to make proteins

Only specific sections of the DNA are read to create the needed proteins for the body

Proteins are a vital component of life and are needed for many things

Enzymes (speed up reactions), hormones (messengers), structural support in cells, transport oxygen

Transcription occurs within the nucleus

A specific gene is copied into mRNA

DNA is used as a template to create a new single strand using A, U, C, and G (U is Uracil and it replaces Thymine)

The mRNA strand leaves the nucleus and enters the cytoplasm of the cell

mRNA attaches to a ribosome where protein synthesis occurs

The ribosome reads the mRNA 3 nucleotides at a time as known as a codon

Each codon sequences a specific amino acid that is brought to the mRNA

Codons are bonded together and fold into the specific 3D structures to form functional proteins

Mitosis: a cell will divide into two identical daughter cells also known as a cell division

Meiosis: Produces sex cells with half of the number of chromosomes, they only have one of each chromosome instead of a pair

When a sperm and egg fuse each one provides 23 chromosomes as a result the new embryo will have 46 chromosomes

as a result the new embryo will have 46 chromosomes

Genes are small segments found at specific places on a chromosome

There are a 2 copies of every gene (1 from mom and 1 from dad)

These different copies are called alleles

Single gene traits are only controlled by one gene with two different alleles

Single gene trait examples: hitch hikers thumb, widow's peak, earlobe attachment

The combination of alleles you get from your parents determines what traits you will have

When alleles from each parent come together one will be dominant while the other will be recessive

Capital letters represent dominant alleles while lowercase letters represent recessive alleles

Example: P = Purple p = white

Allele Combinations

Different traits will be seen depending on the combination of alleles

Two dominant alleles: homozygous dominant

The individual will show the dominant trait ex: PP

Two recessive alleles: homozygous recessive

The individual will show the recessive trait ex: pp

One dominant allele and one recessive allele: heterozygous

The individual will show the dominant trait ex: Pp

Genotype (letters): the allele combinations an organism has

Phenotype (looks): what trait and organism shows

Punnett squares are a tool that can be used to help predict the genetic outcome of an individual

If the parents' alleles are known we can use them to predict the allele combination of the offspring

In situations of complete dominance, the offspring always looked like one of the two allele possibilities

Heterozygous individuals and homozygous dominant individuals show the same phenotype

In situations of incomplete dominance, neither allele is completely dominant over the other

This is often seen when a red flower is crossed with a white flower to produce a pink flower

During codominance, both alleles affect the phenotype in separate ways

In codominance both alleles are equally expressed

Codominant alleles are notated with a capital initial and superscript

Recessive alleles are written as the lower case initial

In humans, the 23rd pair of chromosomes are the sex chromosomes and determine the sex

Males: XY

Females: XX

In males, the Y chromosome is much smaller and does not carry as many genes

Females will have two copies of all the sex-linked genes while males may only have one

Due to this, males will more frequently show the recessive trait of sex-linked genes because they only require one recessive allele

Examples: red-green color blindness, male pattern baldness, and hemophilia

In humans, red-green colorblindness is a recessive sex-linked trait

It is only found on the X chromosome

Because males only have one X chromosome, they have a much greater chance of having red-green colorblindness

Females would have to be homozygous recessive to have red-green colorblindness

Hemizygous

Only having one allele present (A or a)

Type A Blood

IᴬIᴬ or Iᴬ i

Type B Blood

IᴮIᴮ or Iᴮ i

Type AB Blood

IᴬIᴮ

Type 0 Blood

ii

DNA Bases: A - T, G - C

RNA Bases: A - U, G - C

mRNA

messanger ribonucleic acid

amino acids

met … stop